Dissertations / Theses on the topic 'Through-thickness'
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1
Bianchi, Francesco. "Numerical modelling of through-thickness reinforced structural joints." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7992.
Full textAbstract:
The main objective of this research study was to develop numerical models
to analyse the mechanical and fracture properties of through-thickness reinforced
(TTR) structural joints. The development of numerical tools was mainly
based on the finite element (FE) method. A multi-scale approach was used:
the bridging characteristics of a single reinforcement was studied at micromechanical
level by simulating the single-pin response loaded either in mode-I
or in mode-II. The force-displacement curve (bridging law) of the pin was used
to define the constitutive law of cohesive elements to be used in a FE analysis
of the global structure.
This thesis is divided into three main parts: (I) Background, context and
methodology, (II) Development for composite joints, and (III) Development
for hybrid metal-composite joints. In the first part the objectives of the thesis
are identified and a comprehensive literature review of state-of-art throughthickness
reinforcement methods and relative modelling techniques has been
undertaken to provide a solid background to the reader.
The second part of the thesis deals with TTR composite/composite joints. The
multi-scale modelling technique was firstly applied to predict delamination behaviour
of mode-I and in mode-II test coupons. The bridging mechanisms
of reinforcements and the way these increase the delamination resistance of
bonded interfaces was deeply analysed, showing how the bridging characteristics
of the reinforcement features affected the delamination behaviour. The
modelling technique was then applied to a z-pin reinforced composite T-joint
structure. The joint presented a complicated failure mode which involved multiple
crack path and mixed-mode delamination, demonstrating the capability
of the model of predicting delamination propagation under complex loading
states.
The third part of the thesis is focused on hybrid metal/composite joints. Mode-
I and mode-II single-pin tests of metal pin reinforcements embedded into a
carbon/epoxy laminate were simulated. The model was validated by comparing
with experimental tests. Then the effects of the pin geometry on the
pin bridging characteristics were analysed. The model revealed that both in
mode-I and mode-II small pins perform better than large pins and also that
the pin shape plays an important role in the pin failure behaviour. The modelling
technique was then applied to simulate a metal-composite double-lap
joint loaded in traction. The model showed that to obtain the best performance
of the joint an accurate selection of pin geometry, pin arrangement and
thickness of the two adherends should be done.
2
Smith, Carmen Alexis. "Micromechanics of the through-thickness deformation of paperboard." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9426.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 171-172).
An experimental investigation of the behavior of paperboard has been performed, focusing on the identification of the mechanisms of through-thickness deformation. Experiments have been conducted at the microscopic and macroscopic levels, the difference between the two being the length scale. Experiments at the microscopic level were performed in a scanning electron microscope, allowing concurrent viewing of the deformation as it took place with acquisition of load vs. displacement data. The experiments at the macroscopic level confirm the mechanisms observed at the microscopic level and provide more accurate, continuum-level stress-strain data. The motivation for the investigation is the modeling of the creasing process, in which a sheet of paperboard is punched and folded along a narrow line to create a corner for packaging. Creasing experiments indicate that out-of-plane shear damage during punching and normal delamination during folding govern the quality of the resulting crease. Experiments in out-of-plane tension, compression, and simple shear have been performed to investigate the behavior of paperboard under these simple loading conditions. The results show that normal and tangential delamination at the interfaces between layers is of extreme importance in the behavior of paperboard in tension and shear. Damage in the form of micro cracks occurs almost from the onset of strain and culminates in large-scale delamination coincident with a large decrease in the strength of the material. In compression, the behavior is mostly elastic and is governed by densification of the material. The brief initial stages of deformation involve plastic elimination of voids. This is followed by non-linear elastic stiffening of the material via densification.
by Carmen Alexis Smith.
S.M.
3
Mespoulet, Stephane. "Through-thickness test methods for laminated composite materials." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/7314.
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4
Taniguchi, Shinro. "Measurement of the through-thickness strength of composites." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:441ed7e2-72ed-4c2e-b0d2-066b5419b56e.
Full textAbstract:
This research deals with the mechanical characterisation of thick composite laminates in the through-thickness direction. Three independent glass fibre/epoxy laminate configurations, namely cross, quasi-isotropic, and woven, plies were investigated. Six specimen configurations, of which two were developed herein, were employed in order to determine the strength behaviour of these three laminate configurations when subjected to interlaminar shear and interlaminar tensile stresses in isolation and in combination. The stress and strain distributions were estimated using the ABAQUS FEA package. The strain distribution obtained thereby was verified experimentally via Moirandeacute; interferometry which records the exact strain field at the test section. A two dimensional failure envelope is defined for each laminate configuration using the experimentally obtained data. All three independent laminate configurations exhibited almost identical failure envelopes. The woven laminate exhibited superior interlaminar shear strength when subjected to combined interlaminar shear and interlaminar tensile stresses, whereas the cross-ply laminate exhibited superior interlaminar tensile strength when subjected to the same combination of stress. The characteristics of the quasi-isotropic laminate were similar to that of the cross-ply laminate. A partial three dimensional failure envelope was also defined for the materials tested.
5
Grassi, Marcello. "Numerical modelling of composite laminates with through-thickness-reinforcements." Thesis, Cranfield University, 2004. http://hdl.handle.net/1826/2971.
Full textAbstract:
The main objective of the present research study was to develop numerical models to investigate the mechanical properties and effectiveness of z-fibre reinforced laminates. A survey of relevant literature on through-thickness reinforcements (TTR) was undertaken and z-fibre pinning was chosen as the main topic of study. The development of numerical tools was mainly based on the finite element (FE) method and was carried out at different model scale levels.
At a micro-mechanical level of analysis, two models were presented. Firstly a unit cell FE model based on the actual geometric configuration of a z-pinned composite was used. Calculations were performed to understand how the through-thickness reinforcement modified the engineering elastic constants and local stress distributions.
Secondly the study of an analytical micro-mechanical model was undertaken. The model simulated a z-fibre bridging a delamination crack tinder mixed-mode loads. A constitutive law relating the z-pin bridging forces with the crack displacements was defined as the "bridging law". Numerical examples for z-fibre bridging laws under Mode I and Mode II loads were computed along with design evaluations of the effect of several micro-mechanical parameters on the bridging laws. This analytical model was then implemented into a MATLAB code specifically written by the author. The code generated constitutive relationship for interface elements simulating the bridging laws of a single z-pin to be used in a FE analysis.
A detailed numerical study of the mode I interlaminar fracture of composite laminates with z-pins was then carried out. AFL• model of a double cantilever beam (DCB) was developed. The numerical analysis focused on the large scale bridging (LSB) caused by z-pins mechanics, which increased the laminate resistance against delamination growth. The numerical results were validated against experimental data. Computational curves for the energy balance and energy rates were also determined showing that the LSB process consumed a significant amount of irreversible energy. The assumption made by the linear elastic fracture mechanics (LEFM) that all energy dissipations were included in the fracture energy and confined within the damage front, was not valid for z-pinned laminates.
The FE analysis was then extended to study a curved single-lap shear joint, to prove the effectiveness of TTR against debond failure of the joint. The presence of TTR was shown to delay the propagation of the debonding and generally to enhance the load carrying capability of the joint. TTR is proved to be more effective in reducing the Mode I component of debonding driving force than that of the Mode II.
Finally a global-local approach was proposed to implement the TTR elements into large composite stnictural FE models. Possible future studies for TTR numerical modelling were also addressed.
6
Caspe, Russell Jon. "Through-thickness melding of advanced carbon fibre reinforced polymers." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/throughthickness-melding-of-advanced-carbon-fibre-reinforced-polymers(43780bb2-f455-4350-af4c-bd54210b5401).html.
Full textAbstract:
Melding is a novel process which offers a promising route to creating seamless bonds, by partially curing two laminates in a controlled manner using a Quickstep chamber and subsequently co-curing them. Previous research has focused on melding lap joints in the x-y plane of a composite, whereas this study investigates through-thickness melding, or melding in the z-plane of a composite. In this process, two composite stacks were exposed to heat from one side and actively cooled on the other through the z-axis. The two semi-cured parts were then co-cured creating a monolithic part with a seamless bond.The initial stage of the project developed the semi-curing process. After unsuccessful attempts to produce a semi-cured part in a general purpose Quickstep chamber, due to excessive heat transfer, the process was moved to a hot press with independently controlled platens. The hot press succeeded because the platens were separated from each other by the composite plate, unlike the Quickstep bladders which, as they are designed to conform to the part, came into contact allowing for heat transfer. Thermocouples were embedded every 15 plies to quantify the temperature profiles generated through the laminate stack.The next stage of the project developed a process of joining the semi-cured panels to form a through-thickness melded part. The final process involved constraining the sides of the panel with cork edge dams and inserting woven glass fabric at the corners to allow for gasses to escape. However, the outer parts of the fully melded panel exhibited excessive porosity which had an adverse effect on mechanical properties. For example, whereas tensile and flexural moduli measured for material from the edges of the panels were comparable to values reported in literature, the properties of samples from the middle of the panels deteriorated significantly due to the porosity. Mode I interlaminar fracture energy was approximately 10% lower than values measured for panels fabricated in an autoclave.The entire curing process, from semi-curing to a fully melded panel, was characterized extensively. Differential scanning calorimetry was used to determine the degree of cure and values of glass transition temperature (Tg). The degree of cure of the material exposed to the hot side was approximately 50%, the middle 25%, whereas the cold side was only 15% cured. A corresponding Tg profile through the curing process was developed in which the Tg varied from 0 degrees C for the uncured resin to 245 degrees C in highly cured samples. After melding the sample, the degree of cure was found to be in excess of 99%. Rheological studies were carried out to determine the effects of the semi-curing process on resin flow during the melding cycle.Results showed that there was a large transition zone between uncured plies and solid (cured) plies.This thesis demonstrated the broad feasibility of through-thickness melding as a process to create thick composite laminates. However, the complexity of the process gives rise to thermal and rheological phenomena which affect the structural and chemical properties of the fully melded part. The process must therefore be engineered with these factors in mind in order to create a high quality part.
7
Gan, Khong Wui. "Effect of high through-thickness compression on composite failure." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616885.
Full textAbstract:
As composite materials are now used in load conditions with increasing complexity and thickness, all the three-dimensional stress components become important and should be taken into account when predicting failures. In particular, the through-thickness stresses can play a crucial role in determining the in-plane behaviours and strength of a composite, laminate. The work presented in this PhD thesis aims to investigate failures due to complex stress fields at the root of a composite component in a dovetail assembly, where highly concentrated through-thickness stresses as well as in-plane tensile and interlaminar shear stresses are present. The problem was decoupled into two simpler multiaxial load cases which were studied separately: (1) through-thickness compression with interlaminar shear, and (2) through-thickness compression with longitudinal tension. They were investigated experimentally using new loading configuration in a biaxial test machine. This bridges the gap in reliable multiaxial experimental data which is lacking in the open literature. This was then combined with a finite element (FE) modelling approach to, develop simple failure criteria which are validated for engineering design purposes. A simple constitutive law which takes into account the effect of transverse compression and analytical tools which can be I easily utilised to predict stresses and failures in composites were also developed. The findings of this thesis were finally applied to a severely tapered dovetail composite specimen, together with some mitigation strategies, to predict its ultimate fibre failure load and the failure locations.
8
Cui, Guiyong. "Experimental study of the through-thickness strength of laminated composites." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:80258f41-5358-447c-8047-0769c93f062c.
Full textAbstract:
Complicated structures made of fibre reinforced laminates will suffer the failure of delamination which is the main through-thickness failure mode and is usually caused by the combined through-thickness stress state. Three tests, namely the oblique test, the waisted C-specimen test and the notched beam test, have been developed to reveal the failure activities under the combined stress state of in-plane normal stress, through-thickness normal stress and interlaminar shear, and, as a part of the big project, to establish a 3-D failure map in the coordinates of the three stress components. All tests have been analyzed either numerically by FEM or experimentally by Moire interferometry technique. The experimental results have shown that the failure behaviours of laminates are far more complicated than and very different from the traditional metallic materials which can usually be described by phenomenological failure criteria. The phenomenological criteria attempt has been tried and further confirmed that a full experimental understanding is the most important. Moreover, fractographic analysis by SEM has also been conducted to support the test results. Finally the Weibull statistics method has been used to treat the stress gradient effect in the different test geometries while establishing the failure map. It has proved to be a very efficient instrument.
9
Zhang, Bing. "Mechanical performance and self-sensing for through-thickness reinforced composites." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702728.
Full textAbstract:
This dissertation is focused on predicting the mechanical performance and damage self-sensing capability of composite laminates reinforced through the thickness with carbon Z-pins. A micro-mechanical finite element (FE) modelling strategy is developed for the analysis of the through-thickness reinforcement performance of Z-pins. This three-dimensional modelling approach is capable of describing the micro-structural features of Z-pinned laminates based on a versatile ply-level mesh. These features include the actual laminate stacking sequence, the presence of resin pockets surrounding the Z-pin, as well as the inherent misalignment of the through-thickness reinforcement. The Z-pin laminate interface is simulated by cohesive elements and frictional contact. The progressive failure of the Z-pin is modelled considering shear-driven internal splitting, accounted for using cohesive elements, and tensile fibre failure, modelled using the Weibull criterion. The modelling approach is verified via the experimental results of quasi-isotropic laminate coupons reinforced by single T300/BMI Z-pins. Carbon Z-pins enable a delamination self-sensing function in composite laminates. A sensing system able to detect the presence and size of interlaminar cracks in Z-pin reinforced laminates is here proposed and implemented. The system consists of a self-sensing structure, i.e. a Z-pinned laminate, and a sensor reading and analysis (SRA) system. The through-thickness electrical resistance (TTER) is considered as sensing variable. This requires bonding conductive epoxy electrodes to the laminate surfaces. Mode I and II tests are performed on single Z-pin reinforced laminates and double-cantilever laminated beams reinforced with Z-pin arrays. Results show that the TTER ·signal can be used to monitor delamination as well as the bridging state in individual Z-pins. A novel FE modelling strategy is proposed and verified to predict the toughness enhancement due to the insertion of delamination-sensing Z-pins.
10
Rashid, Adnan. "Investigation of through-thickness assembly stresses in composite wing spars." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.722699.
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Saldaeva, Elena. "Through thickness air permeability and thermal conductivity analysis for textile materials." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/13140/.
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Woven fabrics have found enormous application in our daily life and in industry because of their flexibility, strength and permeability. The aim of this work was to create a general model for through thickness air permeability and thermal conductivity for different types of textile fabrics because of their applications in industries and everyday life. An analytical model to predict through thickness air permeability was developed. The objective was to create a model which will take into consideration the two primary mechanisms of air flow in fabrics: through the gaps between yarns and through the yarns. Through thickness air permeability was measured according to British Standard BS EN ISO 9237: 1995. Several fabrics were tested including plain weave, twill weave and satin weave fabrics. The analytical model is a combination Kulichenko and Van Langenhove's analytical model which predicts the permeability through gaps between yams with Gebart's model to predict permeability within yams. Analytical predictions were compared to the experimental data. Computational modelling of through thickness air permeability using Computational Fluid Dynamics CFD software is presented in this thesis. The Polymer Composites Research Group in the University of Nottingham has created a textile schema, named TexGen. The prerequisites of this software were to be able to model various types of textile structures. A CFD model using CFX 11.0 was developed to be able to predict fabric permeability. In addition, an analytical model was developed for fabrics deformed by shear, compaction and tension. Experimental work for through thickness air permeability of sheared fabric was used to verify predicted results. An analytical model for thermal conductivity of fabrics was developed including the influence of moisture content on thermal conductivity. Two existing approaches for single-layer fabrics are described and compared: rule of mixtures and thermal resistance approach. A me6iod for thermal conductivity prediction for multiple layer fabrics is presented. The results are compared to the experimental data and analysed. Some predicted results were in excellent and good agreement with experimental data whereas other predicted results were in poor agreement with experimental data as they were dramatically affected by the assumptions made in the analytical model.
12
Ekmekjian, Nazareth (Nazareth Vahe). "Architecture sandwiched : tuning anisotropy through variable thickness and hetereogeneous laminar assemblies." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99272.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Architecture, 2015.Cataloged from PDF version of thesis. Page 61 blank.
Includes bibliographical references (pages 58-59).
Much of architecture's earliest material palettes and construction methods are often referred to today as legacy materials - those primarily consisting of various types of stone and masonry construction. While these materials are often conceptually thought of as being solid, monolithic, and even homogeneous, in actuality they rely on logics of assembly more akin to contemporary sandwich structures, which are laminar assemblies typically composed of two or more stressed skins and either a solid or cellular core that binds them together. While it is still common to use ancient materials in contemporary architecture, the construction methods and techniques used several hundred years ago are no longer appropriate for today's buildings. This thesis however, argues for a newfound relevance of their influence on contemporary and even future material selections and methods. Specifically, this thesis explores the potentials of composite sandwiches varying in thickness and material in search of architectural possibilities whose structural, formal, and aesthetic implications are a result of tuning multiple influences. Variable thickness is used here as a strategy for enabling a range of architectural and tectonic conditions, all within the same heterogeneous but integrated laminar assemblies. While most commercial products in the realm of composite sandwiches are of uniform thickness in section, this thesis suggests a method for constructing sandwiched elements with variable thickness. This is done primarily through a process of infill and backfill using expanding urethane foam as a medium which creates the so called "core" of the sandwich between two skins. This investigation works through a series of small scale prototypes, each of which focus on a particular tectonic, spatial, or structural condition. These mock ups are meant to serve as didactic artifacts, providing feedback with which to incorporate and speculate upon larger architectural propositions through drawing and representation. The end result is a set of architectural proposals which suggest the beginnings of new design methodologies.
by Nazareth Ekmekjian.
S.M.
13
Gkaliamoutsas, Pantelis. "Modeling fused filament fabrication machine height accuracy through layer thickness variation." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113766.
Full textAbstract:
Thesis: M. Eng. in Advanced Manufacturing and Design, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 85-88).
This thesis addresses the modeling and prediction of total height error of a 3D printed part using a layer-by-layer approach. Layer to layer thickness error is modeled across the build height of Polyactic acid (PLA) and Acrylonitrile butadiene styrene (ABS) parts. A height error compensation model is then formulated and applied at a G-code level to drive the machine to print accurate parts. Preliminary experimentation was done on New Valance Robotics' two fused deposition modeling machine versions, the NVPro and the NVPro High-temp. Results suggested that the layer thickness approach was a viable technique for predicting total part height error. The compensation model for PLA parts was also tested and the compensated parts were significantly closer to the expected part height than the uncompensated prints. However, further experimentation will need to be carried out to solidify a model for ABS parts. Recommendations for future work, measurement method improvement, and model applications are also discussed.
by Pantelis Gkaliamoutsas.
M. Eng. in Advanced Manufacturing and Design
14
Thompson, Luke Francis. "Through-thickness compression testing and theory of carbon fibre composite materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/throughthickness-compression-testing-and-theory-of-carbon-fibre-composite-materials(02ad7cfa-b779-4e69-9361-3c5bb44c6114).html.
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This study investigates the through-thickness behaviour of carbon/epoxy laminates. A through-thickness compression test regime was conducted utilising three specimen designs, which are waisted, hollow cylindrical and cubic specimens. An assessment and comparison of each specimen is given regarding their advantages and disadvantages in characterising the through-thickness response of [+45/-45/90/0]s quasi-isotropic AS4/8552 carbon/epoxy laminates. A finite element (FE) study of the three specimens is presented which results in specimen geometries that provided a macroscopically uniform stress response throughout the gauge length whilst also minimising other features such as stress concentrations. Further to the final geometries being presented, the method of manufacture for the laminate and machining processes for each of the specimens is given. A mesoscopic FE study is presented relating to the free-edge effects induced by through-thickness loading in quasi-isotropic laminates. The results presented show that free-edge effects will be present in the test specimens and will have a larger overall impact on the hollow cylindrical specimen. The free-edge effects also increase the stress concentrations present in the corners of the waisted and cubic specimens. Characteristic stress strain curves are presented for each specimen with strain data taken from post yield strain gauges attached to the specimens. The extracted initial Young's modulus Ez and Poisson's ratios vzx and vzy show a small variation between specimens. The strength values for the three specimens vary greatly with the waisted specimen being the strongest and cylindrical specimen the weakest, indicating that the chosen specimen geometry dominates failure. The experimental data will be used for test case 12 in the Second World Wide Failure Exercise (WWFE-II). A study is presented to predict the effective elastic properties of Z-pinned laminates. The materials under consideration are UD and [0/90]s cross-ply AS4/3501-6 carbon/epoxy laminates. Estimates on the effective properties are provided by two FE approaches and two analytical bounding approaches; namely Voigt and Reuss bounds and Walpole's bounding theory. The two FE approaches are based on extreme assumptions about the in-plane fibre volume fraction in the presence of Z-pins and provide a tight range of values in which the real result should lie. Furthermore, whilst the bounding methods are simple and in the case of Young's moduli produce very wide bounds the selection of the suitable bound result can lead to a good estimate in comparison with the FE data. Typically the best bounding method result for each elastic property is within 10% of the FE predictions.
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Blandford, Peter. "Through-thickness inhomogeneity of steel-sheet texture and its affect on material properties." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59295.
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The work of this thesis centres around two related themes, the first being the characterization of the through-thickness inhomogeneity found in rolled sheet at various stages in its production. The second is involved with attempting to understand how and to what extent the existing inhomogeneity affects the correlations with the anisotropies of some physical or mechanical properties. For this, the inhomogeneity of six steels were measured.Three were specimens removed from the sheet during the early processing of conventional grain-oriented ferrosilicon steel, one sample taken after the first cold rolling stage, another taken after the intermediate anneal, while the last was taken after the following stage, i.e. after the second cold rolling.
To contrast the extensive inhomogeneity expected in the ferrosilicon steels, the remaining three steels consisted of two continuous-annealed, interstitial-free, extra-low-carbon steels and one aluminum-killed, batch-annealed, low-carbon steel, all three of which are commercial final product, deep drawing steels.
16
Henry, B. S. "Constraint based fracture assessment of through-thickness cracks in a bridge girder structure." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637263.
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The Christchurch bridge is a lightweight and readily transportable utility which can be rapidly erected to cover a range of emergency bridging requirements. The bridge is manufactured from a weldable high tensile aluminium alloy. During large scale laboratory fatigue testing, cracks were detected in a tension cord of an I-section bridge girder where damage is most critical. The bridge girder sustained much longer critical crack lengths before failure than estimated assuming linear elastic fracture mechanics conditions and using fracture toughness data obtained from highly constrained geometries. To solve this discrepancy, the current study provides a comprehensive elastic-plastic fracture mechanics assessment of the bridge girder containing through-thickness cracks in the tension chord. Three-dimensional finite element modes of the I-section girders are analysed and a wide range of fracture parameters are evaluated. The bridge girder containing cracks is shown to be a low constraint geometry, where constraint is parameterised by the T-stress and the Q-value. The J-T theory enables the characterisation of the opening stress fields at a distance of 2J/σys ahead of the crack fronts to within 10% of the actual fields evaluated from the finite element analyses. Numerical analyses of a wide range of experimentally tested high and low constraint specimens are used to quantify the relationship between constraint and fracture toughness of the bridge material. Low constraint geometries show up to eight-fold increase in toughness in comparison with high constraint geometries. The J-integral values of the cracked I-section bridge girder models, calculated at the maximum strain levels obtained in the experiments, are matched with those of the specimens through the fracture toughness loci. The I-section results are within the upper boundaries of the loci. The J-T and J-Q theories provide the means of explaining, in terms of loss of constraint, why the bridge girder is able to sustain much longer cracks than first predicted. The loss of constraint enhances the fracture resistance of the bridge girder.
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Dadfar, Humaira. "The influence of variable B horizon thickness (tonguing) on solute transport through undisturbed soil columns." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24456.pdf.
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Verghese, Kandathil Eapen. "Effects of fiber architecture and through-the-thickness stitching on permeability and compaction of textile preforms." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-08292008-063741/.
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Etzberger, Feistauer Eduardo [Verfasser], and Sergio [Akademischer Betreuer] Amancio. "Ultrasonic joining of through-the-thickness reinforced metal-composite hybrid structures / Eduardo Etzberger Feistauer ; Betreuer: Sergio Amancio." Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2019. http://d-nb.info/1175660892/34.
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Mert, Emel. "Effect of air gap thickness and contact area on heat transfer through garments in real life situation." Thesis, Mulhouse, 2016. http://www.theses.fr/2016MULH9978.
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Le corps humain et les vêtements sont toujours en interaction directe avec l’environnement, le corps devant maintenir sa température à environ 37°C. Les transferts de chaleur sont affectés non seulement par les propriétés de l’étoffe constitutives du vêtement, mais également par l’épaisseur de la couche d’air entre le corps et le vêtement. Les propriétés thermiques de la couche d’air dépendent de son étendue, influencée par les courbures du corps humain, des propriétés mécaniques de l’étoffe et de la forme du vêtement. Il est donc nécessaire de déterminer la forme 3D du corps et la répartition, l’étendue et l’épaisseur de la couche d’air ainsi que les zones de contact entre la peau et le vêtement dans des conditions posturales de la vie courante. Dans la présente étude, l’influence thermique de couches d’air homogènes (épaisseur constante) et hétérogènes (épaisseur variable) a été montrée. De plus, la distribution des couches d’air et de l’aire de contact réelle a été analysée minutieusement. L’influence des conditions posturales (à l’aide d’un mannequin) et du mouvement (à l’aide d’un logiciel de simulation de mouvement) a été étudiée dans différents cas. Une méthode de post-traitement des données provenant du logiciel de simulation 3D de mouvement a alors été mise au point. Les résultats montrent que le niveau de confort peut être ajusté en sélectionnant l’étoffe et la forme du vêtement et que cela dépend de la région du corps. La connaissance issue de cette étude sera directement utilisée en modélisation des transferts de chaleur au travers des vêtements et contribue à l’amélioration de la conception des vêtements pour la protection ou la pratique sportiveIn real life, human body and clothing are always in direct interaction with environment, where human body attempts to keep its core temperature constant at around 37 °C by physiological thermoregulatory processes. The heat transfer from the wearer’s body to the environment is affected not only by the fabric properties but also by the presence of air layers and the contact between body and garment. The thermal properties of air layer are related to its size, which in turn, depends on the form of the wearer’s body, mechanical properties of fabric and garment design. Therefore, it is necessary to determine the three dimensional (3D) map and the quantitatively determination of air layers and contact area on the garment in real life situations, such as for various body postures and movement. In the present study, a comparison of the thermal effect of the heterogeneous and homogeneous air layers was sought. Additionally, the distribution of air layers and the contact area for lower body garments were analysed systematically. The effect of various body posture and movement on sought parameters was investigated. Moreover, new method was introduced to post-process the sought parameters for the ready output from 3D simulation software. Consequently, the results of this study indicated that the comfort level of the human body can be adjusted by selection of fabric type and the design of ease allowances in the garment depending on the body region and given purpose. The knowledge gained in this study will be directly used in modelling of the dry and latent heat transfer through garment and contribute to the improvement of clothing design for protective and active sport garments
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Harman, David Edward. "An economic evaluation of the robotic tufting process considering the application of a novel composite wing rib post." Thesis, University of Plymouth, 2013. http://hdl.handle.net/10026.1/10847.
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This thesis aims to establish a greater understanding of the effects of the single-sided robotic tufting process on component manufacturing costs and weight, and subsequently determine whether potential economic benefits can be realised through its implementation. To complete this assessment, the study uses the novel composite rib post application of the Next Generation Composite Wing (NGCW) project as an example case, investigating the component’s manufacturing cost, performance and weight relative to those of a non-tufted rib post with the same initial fabric layup, and a prepreg rib post with the same fibre orientation and fibre volume fraction. Detailed analyses of the tufted composite rib post manufacturing process have established the relationships between its manufacturing activities and the consumed resources, facilitating the creation of a novel cost model incorporating algorithms defining the robotic tufting process, which may be adapted for different geometries and tuft parameters. In addition, novel permeability data for the considered tufted preform have been obtained experimentally allowing the simulation of the liquid composite manufacturing process. The insertion of tufting in the studied arrangement was shown to decrease the in-plane permeability of the preform, reducing the characteristic by a factor of 3.5 in the direction perpendicular to the tuft seams, and 1.8 in the direction parallel. Completing structural analyses and further cost modelling, the study considers the manufacturing costs and weight of each of the studied components when performance is normalised. Implementing weight penalties including lifetime fuel consumption and lifetime revenue, appreciation is given to the potential lifetime costs generated by each of the structural solutions. Comparing the amalgamated costs of each component, relative economy has been evaluated both when considering equipment amortisation and also the use of pre-amortised equipment. Considering lifetime fuel cost/kg as the weight penalty, the novel composite rib post has greater economy within the pure pull-off load case without tufting due to its lower manufacturing costs. However, with the consideration of a more significant weight penalty, such as potential increased lifetime revenue, the use of the novel composite rib post results in superior economy, its lifetime cost/part is estimated to be 14% less than the component without tufting and 61% less than the lifetime cost/part of the prepreg component. Critical evaluations of the project’s methodologies have highlighted the various assumptions made due to the limitations of available information and means to perform certain validations. Under these circumstances the assumptions are believed to be the best representations of what is experienced in reality. As far as possible, errors believed to be the result of assumptions have been accounted for in rigorous error analyses to establish their propagation through the various calculations performed. These analyses have provided confidence in the results of the study, ensuring the significance of the determined economical differences between the investigated components.
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Chipman, Christopher L. "Maximization of Hydraulic Flow through Small Flexible Polymer Tubes by the Optimization of Tubing Stiffness and Wall Thickness." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3728.
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As illness becomes increasingly more common in the United States and across the globe, the need for better and faster medical treatment is greater than ever. The purpose of this work is to evaluate advanced polymers and polymer composites that will provide for increased fluid flow while maintaining outer dimensional, stiffness, and burst resistance characteristics when compared to a currently used material. A polymer configuration consisting of a proprietary formulation that has a durometer approximately 10% higher than the current material with an outer wall thickness of approximately .020" passed a series of tests involving tensile strength, stiffness, flexural fatigue resistance, vacuum lumen collapse resistance and hydraulic burst resistance. This material configuration passed the requirements for applicable test standards and had a tensile strength 13.4% less than the control group, was 52.7% stiffer, did not sustain any noticeable wear or defects during the flexural fatigue test, had a tensile strength 14.8% less that the control group during a post flex fatigue tensile test, did not burst when 150 psi was applied to it for 5 seconds, and is estimated to have a 43% higher flow rate capacity than the current material.
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Zhang, Xuan ZHANG. "Polymer Films With Enhanced Through Thickness Optical Transmission and Compression Modulus with Electric Field Aligned Glass Fiber/Bubbles." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1463961142.
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Zulu, Andrew Wisdom. "Thick Composite Properties and Testing Methods." Thesis, KTH, Lättkonstruktioner, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-243885.
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In most application to date reinforced carbon fiber composites have been used in relatively smaller thickness, less than 10mm thick and essentially for carrying in-plane loads. As a result, design and testing procedures were developed which reflected the need to understand the in-plane response of the material. recently, engineers and designers have begun to use reinforced carbon fiber composites in thicker sections, where an understanding of the through-thickness response is of para-mount importance in designing reliable structures, particularly where the through-thickness strength has a controlling influence on the overall structural strength of the component. In this thesis tests will be done on carbon fiber non-crimp fabric (NCF) which will be loaded in compression and shear and elastic moduli and strength will be evaluated. In characterizing the through-thickness mechanical properties of a composite, the objective is to produce a state of stress in the test specimen which is uniform and will repeatedly measure the true properties with accuracy. In this study, specimens were machined from two blocks of thick (~20 mm) laminates of glass/epoxy and NCF carbon fiber infused with vinylester and tested in compression, and shear.
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McDermott, Patrick M. "Development and implementation of a shell element with pressure variation through the thickness and void growth and nucleation effects." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA369167.
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Thesis (Degree of Mechanical Engineering) Naval Postgraduate School, September 1999."September 1999". Thesis advisor(s): Young W. Kwon. Includes bibliographical references (p. 107-109). Also Available online.
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Harris, Jonathan. "A preliminary study upon the use of novel shaped fibres for the through thickness reinforcement of continuous fibre reinforced plastics." Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428511.
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Chang, Paul, and mrpc@tpg com au. "The Mechanical Properties and Failure Mechanisms of Z-Pinned Composites." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20070111.145714.
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Z-pinning is a through-thickness reinforcement technology for polymer composite materials that has been developed and commercialised over the past fifteen years. The through-thickness reinforcement of composites with thin metallic or fibrous pins aids in suppressing delamination, improving impact damage tolerance and increasing joint strength. Z-pins are applied to the composite part during its manufacture. Pins are embedded within sheets of foam and placed over the unconsolidated part. Subsequently, the foam is compacted and the pins transferred into the part, which is usually an uncured prepreg. In this manner, large numbers of pins can be inserted quickly and easily. The pinned composite is then cured using conventional processes. The use of z-pins is currently limited to several high performance composite structures, most notably Formula One racing cars and F/A-18 E/F (Superhornet) fighter aircraft, although the technology has potential applications in a d iverse variety of aerospace and non-aerospace composite structures. A limited understanding of the mechanical performance of z-pinned parts under high load and fatigue loading conditions currently hinders the application of z-pinned composites. The aim of this PhD project is to investigate the mechanical properties, strengthening mechanics and failure mechanisms of z-pinned carbon/epoxy laminates and joints. The effect of z-pin reinforcement on the tensile and flexural properties of laminates under monotonic and fatigue loading is studied. The sensitivity of these properties to the volume content and diameter of the z-pins is systematically studied by experimentation and analytical modelling. This PhD also evaluates the efficacy of z-pins in improving the load-bearing properties of carbon/epoxy lap joints. Improvements to the room temperature and elevated temperature properties of z-pinned lap joints under monotonic and fatigue tensile loading were determined. The effect of strain rate on the load-bearing properties of z-pinned lap joints was also evaluated. A further aim of the PhD project was to assess the z-pin manufacturing process and the microstructural damage caused by that process. The outcome of this study augments the analysis of the me chanical properties of z-pinned laminates and joints.
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Alali, M. "Through-thickness microstructure and mechanical properties of electron beam similar welded AISI 316L stainless steel and dissimilar welded AISI 316L/Ti6Al4V." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18019/.
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Through thickness microstructure and mechanical properties of defect-free electron beam welded 20 mm thick AISI 316L austenitic stainless steel has been investigated as a function of beam power. The weld microstructure is characterised by a columnar and equiaxed dendritic ferrite in an austenite matrix. The dendritic structure was finer at the bottom of the weld zone. A microstructural boundary called “Parting” was seen along the weld centreline. Tensile tests, using a digital image correlation technique, demonstrated that the highest strain was concentrated in the fusion zone. The bottom section of the weld metal exhibited a yield strength of about 14 – 52 MPa higher than the top section. The ultimate tensile strength in the bottom of the weld was also about 4% higher than the top. The final fracture was detected in the parting region. It was observed from the EBSD scan that the grains in the weld zone contained a weak orientation and showed a high Schmid factor intensity with interception between some strong grains and soft grains at the weld centreline boundary. This explains the high weld ductility and the failure to happen in the parting region. Dissimilar welding of 20 mm thick AISI 316L stainless steel to TiAl6V4 using electron beam welding process was carried out. A successful joint was possible through using of copper sheet with 1.5 mm thick as a transition layer between the two metals. Preheating the weld samples was performed to lower the heat input and reduce the residual stresses. A double pass welding technique was applied to achieve full weld penetration. The weld microstructure was studied by SEM, EDS and XRD. The sensitivity of the microstructure to cracking was evaluated by a microhardness test of the weld cross-section. The weld region near the stainless steel contained Fe and Cu in solid solution. While the weld area near the titanium alloy characterised by the copper solid solution with Cu-Ti and Cu-Fe- Ti intermetallic phases. Ti-Fe intermetallic compounds was suppressed and replaced by relatively soft Cu-Ti intermetallics, which significantly improved the joint toughness. However, the formation of Ti-Cu at the Ti/Cu interface makes this region still susceptible to cracking.
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Pope, P. James (Peter James). "Structural performance of a hybrid sandwich submersible pressure hull : stress and stability analysis of a stiffened cylindrical shell including through-thickness shear." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/37002.
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Lombetti, D. M. "Tufting of complex composite structures." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/11076.
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This study focuses on the effect of tufting on the mechanical and electrical properties of carbon composites using a variety of tuft materials, such as aramid, steel and copper. Several configurations were investigated based on a case study, involving the reinforcement of stiffener-to-skin interfaces of a tail cone. The effect of tuft and base composite material, tufting depth and inclination on the delamination resistance in mode I was evaluated, the associated bridging laws were determined and the failure mechanisms were identified. A simplified superposition model of the delamination response of tufted composites was developed. The electrical performance of tufted composites was determined in simulated lightning strike tests and set against the through-the-thickness electrical conductivity of the materials. The results of mechanical testing showed that the delamination performance depends strongly on the material response of the tufts, with both the bridging behaviour and final toughness levels influenced directly by the strength, ductility and ultimate strain of the tufts. Interactions between the tufts and the surrounding composite, such as interfacial shear and bridging induced by tuft pull-out, play a significant role in the overall behaviour generating a deviation from a simple superposition of the base material and tuft response. The balance between interfacial shear and tuft elongation results in a decreasing trend of delamination toughness with increasing tufting depth for low ductility materials, whilst the trend is reversed for the high ductility copper tufts. This balance is also affected by the properties of the base material, with tougher matrices leading to dominance of shear effects and a weaker enhancement introduced by tufting. Inclination of tufts leads to an increase in crack energy release rate due to the activation of a ploughing mechanism. Metallic and carbon tufts have a positive effect on lightning strike response, with copper tufting offering strike protection at an improved level compared to standard copper mesh solutions.
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田中, 啓介, Keisuke TANAKA, 義明 秋庭, Yoshiaki AKINIWA, 博央 來海, Hirohisa KIMACHI, 和之 伊藤, and Kazuyuki ITOH. "防振ゴム材料における疲労き裂進展挙動へのJ 積分の適用." 日本機械学会, 2003. http://hdl.handle.net/2237/9154.
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Smith, Jr Richard Lee. "ANALYSIS OF THICKNESS VARIATIONS OF THE AUX VASES FORMATION IN WHITE COUNTY, ILLINOIS THROUGH APPLICATION OF GEOPHYSICAL WELL LOGS AND 3-D SEISMIC REFLECTION ATTRIBUTES." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1731.
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A two square mile (5.2 square kilometer) 3-D seismic reflection survey was completed in northeastern White County, Illinois for petroleum exploration in January of 2008. Well log data was made available from Royal Drilling and Producing, who contracted the seismic survey, and additional data was retrieved from the ILOIL database. Raster (TIFF format) images that were available for nearly every well location in the study area were calibrated for depth and stratigraphic tops picked. The purpose of this study is to analyze the Aux Vases formation using 3-D seismic reflection data and attribute analysis by comparing this data to well log information that is greatly available in the study area. Synthetic seismograms were calculated to calibrate seismic reflection data time to actual geological depth to a formation. The synthetic seismograms were calculated using wavelets extracted from the 3-D seismic data and edited, digital (LAS format) sonic and density logs measured in three wells. Geophysical log data from wells in the area were used to interpret formation top and bottoms. With the Aux Vases and Ste. Genevieve top information, an isopach was generated. Horizons were handpicked in all 318 seismic lines and isochron maps were generated to compare time thickness to actual thickness of the isopach maps. Attribute analysis was performed on horizon and volume cubes to interpret the Aux Vases formation in the study area. These attributes included instantaneous phase, instantaneous amplitude, and instantaneous frequency. Additionally, multiple spectral decomposition cubes (from four SEG-Y volumes) were generated for 520-580 ms intervals and interpreted at 550 ms. The combination of this data lead to identification of two larger stratigraphic bodies and several smaller ones in the study area. Thickness comparison between these attributes and isopach maps was completed and found similarities that can be used to determine potential thickness. A thickness estimate was completed at Well B using the frequency from spectral decomposition. A channel was mapped in the western edge of the survey using spectral decomposition and other attributes. Finally, a fault was identified in the southeastern portion of the survey area.
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Barrientos, Nava Juan Rene 1972. "Resistência ao micro-cisalhamento de cimentos resinosos fotoativados através de diferentes espessuras de cerâmica = Micro-shear bond strength of resin cements photoactivated through different ceramic thickness." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/288537.
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Orientador: Rafael Leonardo Xediek ConsaniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: O objetivo neste estudo foi avaliar a resistência da união ao cisalhamento de cimentos resinosos fotoativados através de diferentes espessuras de cerâmica e o modo de fratura. Foram utilizados os cimentos resinosos RelyX U200 (3M ESPE) e Variolink II (Ivoclar-Vivadent). Sessenta discos de cerâmica IPS Empress Esthetic (Ivoclar-Vivadent) com 12mm de diâmetro foram separados em grupos (n=10) segundo a espessura (0,7; 1,4 e 2,0mm). A superfície dos discos foi condicionada com ácido hidrofluorídrico a 10% por 60s, lavada e seca com jato de ar por 60s. A seguir foi feita aplicação de agente silano por 60s. Uma matriz de elastômero com forma de disco com 15mm de diâmetro e 0,5mm de espessura com quatro orifícios de 1,5mm de diâmetro foi usada para delimitar a área de adesão na cerâmica. A manipulação dos cimentos resinosos foi de acordo com as instruções dos fabricantes, o material inserido nos orifícios da matriz, recoberto com tira de poliéster e lâmina de microscópio com pressão digital. A fotoativação foi realizada através do disco de cerâmica com Ultra Lume LED 5 (Ultradent) com potência de 1200 mW/cm² por 60s. Após armazenagem por 24h em água destilada a 37ºC, os corpos-de-prova foram avaliados com lupa estereoscópica para descartar aqueles com imperfeições. O teste de resistência ao cisalhamento foi conduzido em máquina de Ensaio Universal Instron (Canton, MA, USA), com velocidade de 1 mm/min e com célula de carga de 50Kg até fratura e os valores de resistência da união calculados em MPa. O modo de fratura foi analisado com lupa estereoscópica (LABOMED, Barueri, SP), com aumento de 10 vezes. Os resultados foram submetidos à análise de variância de dois fatores e teste de Tukey (5%). Os modos de fratura foram considerados em função da predominância das falhas sendo a falha coesiva em cerâmica a que prevaleceu. Os resultados mostraram que a interação entre os fatores espessura da cerâmica e cimento, e o fator espessura não foram significantes (p=0,541 e p=0,643, respectivamente), enquanto o fator cimento foi significativo (p=0,009). Pode-se concluir que o cimento Variolink II apresentou resistência de união significantemente maior que a do cimento RelyX U200
Abstract: The aim of this study was to evaluate the bond shear strength of resin cements photoactivated through different thicknesses of ceramics and the failure mode. RelyX U200 (3M ESPE) and Variolink II (Ivoclar Vivadent) resin cements were used. Sixty ceramic discs of Esthetic IPS Empress (Ivoclar-Vivadent) with 12mm diameter were divided into groups (n=10) according to their thickness (0.7; 1.4 and 2.0mm). The grounded surface was etched with 10% hydrofluoric acid for 60 seconds, rinsed and dried with compressed air for 60s. The following silane application was made for 60s. An elastomeric matrix having 15mm in diameter and 0.5mm in thickness with four holes (1.5mm in diameter) was used to define the adhesion area in the ceramic. The manipulation of the resin cements was carried out according to the manufacturers¿ instructions and inserted into the holes of the elastomer matrix, covered with plastic strip and finger pressed with a microscope slide. Light curing through ceramic was Ultra Lume LED 5 (Ultradent) with power 1200mW/cm² for 60s. After storage for 24h in distilled water at 37ºC, all resin cylinders were checked under magnification. The shear strength test was conducted in a Instron Universal Testing Machine, at cross-head speed of 1mm/min with load of 50Kg until fracture. The bond strength values were calculated (MPa). The fracture mode was analyzed using stereoscopic lens 10x (LABOMED, Barueri, SP). The results were submitted to two-way ANOVA and the means compared by Tukey¿s test (5%). Cohesive failure mode within ceramic was predominant. The results showed that the interaction between the factors and cement thickness, and the thickness factor were not statistically significant (p=0.541 and p=0.643, respectively). The cement factor was significant (p=0.009). In conclusion, the Variolink II showed significantly higher bond strength value than the RelyX U200 cement
Mestrado
Materiais Dentarios
Mestre em Materiais Dentários
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Feng, Chi. "SOFT X-RAY FORMATION MEASUREMENT OF LOW DENSITY MATERIALS AND COMPRESSIVE RESPONSE CHARACTERIZATION." Miami University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=miami1350679879.
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Arun, Sutham. "Finite element modelling of fracture & damage in austenitic stainless steel in nuclear power plant." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/finite-element-modelling-of-fracture-and-damage-in-austenitic-stainless-steel-in-nuclear-power-plant(031e5ceb-b3b5-4499-8094-dbe362e27ff7).html.
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The level of residual stresses in welded components is known to have a significant influence on their failure behaviour. It is, therefore, necessary to understand the combined effect of mechanical loading and residual stresses on the ductile fracture behaviour of these structures in order to provide the accurate structural safety assessment. Recently, STYLE (Structural integrity for lifetime management-non-RPV component) performed a large scale bending test on a welded steel pipe containing a circumferential through-thickness crack (the MU2 test). The purpose of this test is to study the impact of high magnitude weld residual stresses on the initiation and growth of cracks in austenitic stainless steels. This research presents the simulation part of the STYLE project which aims to develop the finite element model of MU2 test in ABAQUS to enhance the understanding and ability to predict the combined influence of mechanical loading and residual stresses on the ductile fracture behaviour of nuclear pressure vessel steels. This research employs both fracture mechanics principles (global approach) and Rousselier damage model (local approach) to study this behaviour including crack initiation and growth. In this research, the Rousselier model was implemented into ABAQUS via the user defined subroutines for ABAQUS/Standard and ABAQUS/Explicit modules, i.e. UMAT and VUMAT. The subroutines were developed based on the integration algorithm proposed by Aravas and Zhang. The validation of these subroutines was checked by comparing the FE results obtained from the implementation of these subroutines with the analytical and other benchmark solutions. This process showed that UMAT and VUMAT provide accurate results. However, the UMAT developed in this work shows convergence problems when the elements start to fail. Hence, only VUMAT was used in the construction of the finite element model of the MU2 test. As mentioned above, the results obtained from both fracture mechanics approach and Rousselier model are compared with the experimental data to validate the accuracy of the model. The results shows that both fracture mechanics approach and the Rousselier model predict similar final crack shapes which correspond closely to the test results in south direction. The other conclusions about the influence of residual stress on ductile fracture obtained from this work are also summarized in this thesis.
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Joesbury, Adam Michael. "New approaches to composite metal joining." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/10009.
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This thesis explores new methods for achieving load-carrying joints between the dissimilar materials of continuous fibre reinforced polymer matrix composites and structural metals. The new composite-to-metal joining methods investigated in this work exploit the metal-to-metal joining techniques of arc micro-welding, resistance spot welding, and metal filler brazing, to form novel micro-architectured metal adherends that can be used for enhanced composite-to-metal joining. Through a combination of equipment instrumentation and metallographic inspection of fabricated prototype joints, understanding is gained of how materials respond when processed by manufacturing techniques that have not previously been exploited for dissimilar material joining. Mechanical testing of prototype joints; both to ultimate loading strength and partial failure states, with subsequent inspection of specimens and comparative performances evaluation enabled joining performance characterisation of the new joining methods. Key results include: the identification of micropin reinforced adhesive joints to exhibit pseudo-ductile failure characteristics, resistance spot weld reinforcement of adhesive joints to boost bonding performance, and the use of a polymer infused metal foam to overcome difficulties of thermoplastic to metal adhesion. Through this work knowledge of how novel micro-architectures reacted under mechanical loading enabled insights to be gained into how perceived manufacturing defects can benefit joining performance. Such examples include, localised material weakness that lead to global pseudo-ductile failure behaviour, and low-strength secondary joining mechanisms boosting primary load transfer systems. By comparison of the diverse joining methods investigated in this work, trends were identified that suggest joining performance between the two dissimilar materials is improved by increasing the direct interaction between the composite reinforcement fibres and the metal structure. It is demonstrated that joining improvements are gained by forming mechanical connections between metals and composite precursory material before the final manufacturing process of the composite.
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Martins, Alan. "Analysis of damage mechanisms in composite structures reinforced by tufting." Thesis, Compiègne, 2018. http://www.theses.fr/2018COMP2443/document.
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Cette étude portait sur l’évaluation des performances mécaniques et des mécanismes de défaillance des composites cousus dans différentes conditions de chargement. Des plaques stratifiées et des raidisseurs renforcés par tufting ont été fabriqués avec différents paramètres de couture afin d'évaluer leur effet sur les propriétés des composites. L'investigation a été assistée par une caractérisation multi-instrumentée pendant les tests. Les plaques cousues soumises à des tests de cisaillement à poutre courte sont utilisées dans l'analyse du comportement de la densité et de l'angle de couture dans des conditions de chargement en mode II, tandis que des tests d'impact et de compression après impact (CAI) sur la tolérance aux dommages. Des tests de fatigue en éprouvettes trouées ont également été réalisés afin d’évaluer la réponse des coutures, en particulier leur position par rapport au trou central, à la concentration de déformation générée par le trou. La suite de ce travail a consisté en des tests mécaniques sur panneau raidi oméga renforcé par tufting. La procédure a optimisé les paramètres de touffetage utilisés pour renforcer les structures du lot précédent d'échantillons jusqu'à atteindre un point optimal où les propriétés principales, principalement trouvées dans les tests d'arrachement, sont égales ou supérieures à celles des échantillons témoins. Cette amélioration tenait également compte des modifications de la forme des raidisseurs. En outre, une nouvelle approche basée sur l’effet piézorésistif des coutures en fibres de carbone lors du chargement des éprouvettes composites est réalisée. Cela peut faciliter la surveillance de l’état de santé des fils cousus et donc du composite en raison de la nature structurelle des coutures. Les résultats ont montré que les renforts par tufting sont capables d'augmenter considérablement la ténacité entre les composites et la tolérance aux endommagements des composites, principalement en raison de leurs phénomènes de pontage des fissures. Les paramètres de tufting sont des facteurs décisifs pour obtenir les meilleures propriétés mécaniques. Cependant, ces travaux ont montré que les fils de coutures sont également responsables de la création de fissures dues à la concentration de contrainte et aux défauts causés par leur insertion et, par conséquent, à la diminution de la résistance des composites. L'enquête conclut que l'insertion aléatoire des touffes n'est pas idéale pour la performance du matériau et doit donc être évitée. Le développement de l'insertion des coutures dans les raidisseurs oméga a été soutenu par la caractérisation multi-instrumentée qui a permis d'optimiser le renforcement de la structure. Bien que l’étude ait permis d’obtenir des propriétés mécaniques nettement supérieures à celles des panneaux oméga renforcés par touffetage, il est évident que la procédure employée n’est pas optimale. Le présent travail propose également un modèle préliminaire d'éléments finis pour surmonter le coût et la perte de temps des tests expérimentaux. Il vise principalement à optimiser les paramètres de tufting dans la structure. Le modèle développé était capable de prédire les mêmes endommagements que ceux observés expérimentalement, mais encore éloignés des prévisions quantitatives des résultats. Le contrôle de l’état structurel des stratifiés composites cousus par les fils de carbone semble prometteur et pourrait aider à l’avenir à fournir des informations sur l’état de santé des coutures sous chargement qui ne sont pas atteintes par les méthodes de caractérisation classiques utilisées dans ce travailThis study focused mainly on the assessment of the mechanical performance and the failure mechanisms of tufted composites under divers loading conditions. Laminated plates and stiffened panels reinforced by tufting was manufactured with different tufting parameters to evaluate their effect in the properties of the composites. Multi-instrumented characterization carried out during the tests assisted the investigation. The tufted plates subjected to short-beam shear tests aided especially in the behavior analysis of tufting density and angle in mode Il loading condition, while impact and compression after impact (CAI) tests on the damage tolerance. Open-hole fatigue tests were also performed to evaluate the tufts response, especially regarding their position to the center hole, to the strain concentration factor generated by the hole. The following part of this work consisted of the mechanical tests on omega stiffened panel reinforced by tufting. The procedure optimized the tufting parameters employed for reinforcing the structures from the previous batch of specimens until reaching an optimal point that the main properties, primarily found in pull-off tests, are equal or superior to those of the control specimens. This improvement also considered the modifications in the shape of the stiffeners. Furthermore, a novel approach based on the piezoresistive effect of carbon tufts under loading of the composite specimens is performed. This may support the monitoring of the health status on the tufted threads and therefore of the composite because of the structural nature of the tufts. The results showed that tufting reinforcements are capable of increasing the interlaminar fracture toughness and damage tolerance of the composites considerably owing mainly to their crack bridging phenomena. The tufting parameters are decisive factors for achieving the best mechanical properties. However, this work reported that tuft threads are also responsible for generating cracks due to the strain concentration and defects caused by their insertion and consequently, can decrease the strength of the composites. The investigation concludes that the random insertion of the tufts is not ideal for the performance of the material and thus must be avoided. The development of the tufting insertion in the omega stiffeners was supported by the multi-instrumented characterization that led to optimizing reinforcement in the structure. Although the study achieved the goal of obtaining mechanical properties significantly superior to the omega panels reinforced by tufting, it is noticeable that the procedure employed is not optimal. The present work also proposes a preliminary finite element model to overcome the costly and time consuming of the experimental tests. It intends primarily optimizing the tufting parameters in the structure. The model developed was capable of predicting the same damage events as observed experimentally, but it still distant from the quantitative predictions of the results. The structural health monitoring of the tufted composite laminates by the carbon threads seems promising and could help in the future for supplying data about the tufts health status under loading that are not achieved by the conventional characterization methods employed in this work
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Lin, Weiwei, Kai Chen, Shufeng Zhang, and C. L. Chien. "Enhancement of Thermally Injected Spin Current through an Antiferromagnetic Insulator." AMER PHYSICAL SOC, 2016. http://hdl.handle.net/10150/614754.
Full textAbstract:
We report a large enhancement of thermally injected spin current in normal metal (NM)/antiferromagnet (AF)/yttrium iron garnet (YIG), where a thin AF insulating layer of NiO or CoO can enhance the spin current from YIG to a NM by up to a factor of 10. The spin current enhancement in NM/AF/YIG, with a pronounced maximum near the Neel temperature of the thin AF layer, has been found to scale linearly with the spin-mixing conductance at the NM/YIG interface for NM = 3d, 4d, and 5d metals. Calculations of spin current enhancement and spin mixing conductance are qualitatively consistent with the experimental results.
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Tsivoulas, Dimitrios. "Effects of combined Zr and Mn additions on the microstructure and properties of AA2198 sheet." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/effects-of-combined-zr-and-mn-additions-on-the-microstructure-and-properties-of-aa2198-sheet(6bb2c9db-7584-464b-8064-bab0cc2d397c).html.
Full textAbstract:
The effect of individual and combined zirconium and manganese additions have been compared for an AA2198 6 mm thick sheet in T351 temper regarding their influence primarily on recrystallisation resistance and secondly on fracture toughness and overageing resistance. A complete characterisation of the dispersoid distributions was carried out for a deeper understanding of the effects of the Al3Zr and Al20Cu2Mn3 particles, involving studying their formation from the as-cast and homogenised stage.The most important finding in this work was the lower recrystallisation resistance in the alloy containing 0.1 wt%Zr + 0.3 wt%Mn compared to that containing only 0.1 wt%Zr. This result was rather unexpected, if one considers the opposite microsegregation patterns of Zr and Mn during casting, which leads to dispersoids occupying the majority of the grains’ volume and minimising dispersoid-free zones that could be potential sites for nucleation of recrystallisation. The other two alloys with dispersoid additions 0.05 wt%Zr + 0.3 wt%Mn and 0.4 wt%Mn, were partially and fully recrystallised respectively in the rolled T351 condition.Equally important in this work, was the observation that the opposite microsegregation trend of Zr and Mn sufficed to restrict grain growth in unrecrystallised areas. The 0.1Zr-0.3Mn alloy exhibited the lowest grain size of all alloys, both in the T351 temper and after annealing at 535oC for up to 144 hours. The reason for this was the combined action of Al20Cu2Mn3 dispersoids and Mn solute in the regions where the Zr concentration was low (i.e. near the grain boundaries), which offered additional pinning pressure to those areas compared to the 0.1Zr alloy.The lower recrystallisation resistance of the 0.1Zr-0.3Mn alloy was explained on the grounds of two main factors. The first was the lower subgrain size and hence stored energy within bands of Al20Cu2Mn3 dispersoids, which increased the driving force for recrystallisation in these regions. The second was the interaction between Zr and Mn that led to a decrease in the Al3Zr number density and pinning pressure. Since Zr was the dominant dispersoid family in terms of inhibiting recrystallisation, inevitably this alloy became more prone to recrystallisation. The Al3Zr pinning pressure was found to be much lower especially within bands of Al20Cu2Mn3 dispersoids. The detrimental effect of the Mn addition on the Al3Zr distribution was proven not to result from the dissolution of Zr within Mn-containing phases, and several other phases, at the grain interior and also in grain boundaries. The observed effect could not be precisely explained at this stage.Concerning mechanical properties, the 0.1Zr alloy exhibited the best combination of properties in the Kahn tear tests for fracture toughness. Further, it had a higher overageing resistance compared to the 0.1Zr-0.3Mn alloy.As an overall conclusion from this work, considering all the studied properties here that are essential for damage tolerant applications, the addition of 0.1 wt%Zr to the AA2198 6 mm thick sheet was found to be superior to that of the combined addition of 0.1 wt%Zr + 0.3 wt%Mn.
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Cozzens, Paul. "A Study on the Thickness of Plate Washers for Anchor Rod Applications." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627665709614063.
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Atilgan, Ahmet Koray. "A Study Of Laminar Forced Film Condensation Of Vapor Flowing In Cross-flow Direction Through The Annular Space Between Two Concentric Cylinders." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607714/index.pdf.
Full textAbstract:
In this study laminar forced film condensation of vapor flowing in cross-flow
direction through the annular space between two concentric cylinders was
investigated numerically. To achieve this, governing equations of the vapor and the
condensate flow in cross-flow direction between two concentric cylinders were
developed. After obtaining the equations in integral forms by using the finite
difference technique the vapor boundary layer thicknesses on the inner and outer
cylinders and the condensate layer thickness was obtained as a function of the
angular position on the cylinders. It was assumed that the condensation took place on
the outer surface of the inner cylinder only and the outer cylinder was assumed to be
insulated. The computer program developed is capable to calculate the condensate
film thickness, vapor boundary layer thickness, the heat flux and the heat transfer
coefficient and the interface velocity between the condensate and the vapor layer as a
function of the angular position on the cylinders. Effects of changing the free stream
velocity flowing in the channel, the radius of the inner cylinder, the temperature
difference between the saturated vapor and the wall and the annular space between
the concentric cylinders were investigated numerically by using the computer
program and the results were presented graphically. Results showed that by
increasing the free stream velocity of the vapor in the core, the film thickness
decreased and by increasing the radius of the inner cylinder, the temperature
difference between the saturated vapor and the wall and the annular space, the film
thickness increased.
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Guillotin, Alban. "Étude de la rugosité de surface induite par la déformation plastique de tôles minces en alliage d'aluminium AA6016." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2010. http://tel.archives-ouvertes.fr/tel-00716025.
Full textAbstract:
Dans le cadre d'un programme de recherche visant à l'allègement de la structure des véhicules, l'origine de lignage dans des tôles en aluminium AA6016 a été étudiée. Ce phénomène, qui peut apparaître à la suite d'une déformation plastique, est apparenté à de la rugosité de surface alignée dans la direction de laminage (DL). Sa présence est néfaste à une bonne finition de surface, et son intensité est appréciée visuellement par les fabricants.Une méthode de quantification rationnelle a été développée. La caractérisation de la distribution morphologique des motifs de rugosité a été rendue possible par l'utilisation de fonctions fréquentielles telle la densité de puissance spectrale. La note globale, construite à partir de la quantification individuelle des composantes de lignage pur et de rugosité globulaire, s'est montrée en bon accord avec les estimations visuelles, et notamment avec le niveau de lignage intermédiaire regroupant plusieurs aspects de surface différents.La microstructure des matériaux à l'état T4 a été expérimentalement mesurée couche de grains par couche de grain à l'aide d'un couplage entre polissage contrôle et acquisition par EBSD. Les 4 à 5 premières couches sous la surface (-120μm) semblent jouer un rôle mécanique prépondérant dans la formation du lignage car elles offrent à la fois une grande taille de grains moyenne, une importante ségrégation d'orientations cristallines, et une forte similitude de longueurs d'onde entre la rugosité de surface et les motifs de la microtexture.Des simulations numériques ont permis de vérifier que les couples de texture identifiés (Cube/Goss, Cube/Aléatoire et Cube/CT18DN) possédaient des différences d'amincissements hors-plans suffisantes pour générer l'ondulation d'une couche d'éléments. En revanche, l'influence mécanique de cette même couche décroit très rapidement avec son enfouissement dans la profondeur et devient négligeable sous plus de 4 couches d'éléments.
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Mansfield, Byron Allen. "Analysis of Finite Length, Orthotropic Composite Cylinders Including Through-Thickness Shear Effects." Thesis, 2007. http://hdl.handle.net/10539/2071.
Full textAbstract:
Student Number : 0001361N -
MSc(Eng) dissertation -
School of Mechanical, Industrial and Aeronautical Engineering -
Faculty of Engineering and the Built EnvironmentThick composite cylinders are important structural elements which cannot be analysed by traditional techniques due to through-thickness effects. This work presents analyses for thick composite tubes of finite length including through-thickness shear. A numerical thermal analysis is implemented for the determination of the transient through-thickness behaviour of tubes. A me- chanical analysis, based on the Rayleigh-Ritz technique, is presented which analyses finite length, composite tubes under a variety of loadings. The anal- yses are shown to be accurate and efficient and are validated against existing results. Results are presented for two ring-stiffened tubes under pressure and thermal loading and also for the transient thermal behaviour of these tubes. It was found that both the through-thickness and transient effects are of im- portance as the stress variation through the thickness and with time was significant for both tubes.
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Liu, Yi-Hong, and 劉奕宏. "Optical Constant and Thickness Measurements through Multi-wavelength Interferometry." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/88318613106113659640.
Full textAbstract:
碩士國立中央大學
光電科學研究所
98
In this thesis, there were two major parts, software and the hardware parts, for measuring the optical constants and thickness of the thin film. For the software, we used novel Genetic Algorithm to design our program. For the hardware, we proposed a polarization phase shifting interferometer based on Twyman-Green interferometer structure. In our arrangement, the low coherence light source is composed of a mercury lamp, which is a polychromatic light source and covering the visible spectral range, and a narrow band pass filter to create a Gaussian power spectral density source. We chose five color filters (532nm, 580nm, 632nm, 690nm, 730nm) for selecting wavelengths. In the polarization interferometer, a novel pixelated mask with a micro-polarizer phase shifting array was placed just in front of the CCD, so that we can use single shot to extract phase information and it is effective to reduce environmental vibration. Then we can get the spectrums from U4100 spectrometer made by HITACHI, and use genetic algorithm to write a fitting program to get the refractive index and thickness of single-layer thin film. We used two parts, transmittances only and transmittances plusing with phases, to process our problems. All the researches need only five phases and spectrums can derive multi-wavelength refractive index and thickness. The measurement results were compared with the results obtained by SOPRA ellipsometer. The results meet reasonable values in both refractive index and thickness.
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Wang, Ying-ching, and 王瀅晴. "Through-Thickness Behavior of High Strength Thick Steel Plate." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/84513370153799518356.
Full textAbstract:
碩士國立臺灣科技大學
營建工程系
97
Structural steel usually possesses various chemistries. These chemistries may affect the mechanical property of the steel, degenerate the weldablity and the structural performance. During the rolling process of the steel plate, the non-metallic magnesium sulfide (MnS) inclusions of the steel are flattened. These flattened inclusions may induce the lamellar tearing when the steel plate is subjected to the out-of-plane force. The possibility of lamellar tearing greatly increased if thick plate is used. This reported research examined the through thickness behavior of the jumbo size steel plate. Three different steel, A572 Gr.50, SM490B and SN490C are examined. The experimental program is designed to simulate the most rigorous situation in the area of beam-to-column connection. The jumbo steel plate is weld to the diaphragm plate by high heat input welding, EGW, and to the beam flange by FCAW weld. A cruciform specimen is used and the jumbo plate is subjected to out-of plane pulling force. These studies show that the through thickness behavior of jumbo plate is sensitive to the loading conditions and the types of the steel.
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Liew, Kah-Khan, and 劉家勤. "Propagation Characteristics of Thickness-Through-Cracks in Irregular Stress Distribution Fields." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/24191834066413571395.
Full textAbstract:
碩士國立成功大學
造船及船舶機械工程學系
90
ABSTRACT The propagating characteristics of thickness-through-cracks in irregular stress distribution fields are discussed in the present paper. Three kinds of specimen having different size of defects on the both surfaces or steel sheets are designed (hereafter referred or as “defective specimen”) to produce irregular stress distribution fields. Using defective specimens and common CCT specimens (referred to as “flat specimen”) fatigue crack propagating tests were carried out. During the tests, crack growth fates and closure load were measured, and the beach marks used to record the shape of crack tip were introduced. For an analysis purpose, stress distribution and plastic zone of defective specimens are calculated be finite element analysis. As the results, although all of the specimens are subjected to the same cyclic loading, defective specimens have higher closure loads and longer fatigue propagation life than that of flat specimens. Taking the closure loads into account and using effective stress intensity range, , to assess the propagation life, a precise prediction can be obtained. Also, the shape of beach marks obtained from defective specimens differs from that of flat specimen and is highly stress distribution dependent. Finally, an approach to estimate the growth rate of thickness-through-cracks in irregular stress distribution fields is proposed.
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鞠, 暁臣, and Xiaochen Ju. "Study on Propagation of Through-thickness Fatigue Crack Subjected to Out-of-plane Bending." Thesis, 2012. http://hdl.handle.net/2237/17334.
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Lin, Jan T. "Enhancing the through-thickness thermal conductivity of carbon fiber polymer-matrix composites by nanostructuring." 2007. http://proquest.umi.com/pqdweb?did=1483472951&sid=2&Fmt=2&clientId=39334&RQT=309&VName=PQD.
Full textAbstract:
Thesis (M.S.)--State University of New York at Buffalo, 2007.Title from PDF title page (viewed on June 18, 2008) Available through UMI ProQuest Digital Dissertations. Thesis adviser: Chung, Deborah D. L. Includes bibliographical references.
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Yi, Sung, and Lin-Quan Yao. "Solid-shell element model of assumed through-thickness electric distribution for laminate composite piezoelectric structures." 2002. http://hdl.handle.net/1721.1/3988.
Full textAbstract:
The eight-node solid-shell finite element models have been developed for the analysis of laminated composite pate/shell structures with piezoelectric actuators and sensors. To resolve the locking problems of the solid-shell elements in laminated materials and improve accuracy, the assumed natural strain method and hybrid stress method are employed. The nonlinear electric potential distribution in piezoelectric layer is described by introducing internal electric potential. The developed finite element models, especially, electric potential node model, have the advantages of simpler modeling and can obtain same effect that exact solution described.Singapore-MIT Alliance (SMA)
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Che-JueiWu and 吳哲睿. "Thermal interface materials having hybrid fillers for enhancing through-thickness thermal conductance and increasing electrical resistance." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/wzw6hv.
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