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1
Khoo, Heng Aik. "Ductile fracture of steel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0014/NQ59610.pdf.
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2
Simsir, Mehmet. "Investigation Of Fracture Behavior Of Steel/steel Laminates." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604834/index.pdf.
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A study is carried out into fracture behavior of steel/steel laminates both experimentally and through finite element analysis (FEM). The laminates produced by hot pressing consisted of low carbon and medium carbon steels with two volume fractions0.41 and 0.81. Fracture toughness, JIC has been measured using partial unloading technique assuming a critical value of crack extension. The technique is initially applied to monolithic material and then to the laminates in crack divider orientation. Evaluation of fracture toughness of laminates indicates that there is a substantial improvement of JIC with increase in the volume fraction. The systems under study were also evaluated by FEM modeling with the use MARC package program. To evaluate JIC, the problem has been evaluated in several steps
first two-dimensional plane strain problem is considered. This is followed by three-dimensional case and then by an artificially layered system, all for monolithic materials. Values of JIC derived were close to one another in all cases. Following this verification, the method, as implemented in layered monolithic system, was applied to laminates. This has shown that JIC of laminates can be predicted using FEM analysis, including the delamination. Values of JIC varied in the same manner as the experiment verifying that fracture toughness in the current system increases with increase in volume fraction. It has been concluded that modeling as implemented in this work can be used for useful composite systems incorporating hard/brittle reinforcements both in crack divider and crack arrester orientation.
3
Smith, Gillian. "Modelling fracture in ferritic steel." Thesis, University of Surrey, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250880.
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4
Liu, Kaiyuan. "Fracture properties of heat-straightened steel." Laramie, Wyo. : University of Wyoming, 2006. http://proquest.umi.com/pqdweb?did=1296091021&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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5
Druiff, Helen. "Micro-mechanisms of ductile fracture." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385328.
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6
O'Donnell, I. J. "Ductile fracture in type 316 stainless steel." Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356270.
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7
Luken, Raymond C. "Fracture behavior of CPM 10V." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/90974.
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The effect of three heat treatments on plane-strain fracture toughness (K Ic), fatigue crack growth rate (da/dN), and tensile behavior of a commercial powder metal alloy, CPM 10V, was investigated. Fracture toughness was increased by increasing the tempering temperatures and decreased by increasing the austenitizing temperature. These changes were related to changes in yield strength and the resulting crack tip plastic zone sizes. Fracture toughness resulting from any of the three heat treatments was inversely related to the hardness. Fatigue crack growth followed the Paris Law for some portion of the curve and crack growth exponents, n, were virtually unchanged by the heat treatment. The linear portion of the growth curve was shifted to higher stress intensity ranges for heat treatments yielding higher fracture toughness. Fatigue crack growth behavior in the high growth region was determined mainly by the fracture toughness of the specific heat treatment.M.S.
8
Wu, Shang-Xian. "Fracture analyses and toughness : measurement of specimens with deep and shallow cracks." Thesis, The University of Sydney, 1990. https://hdl.handle.net/2123/26383.
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Slip—line field analyses and finite element analyses have been conducted for three— and four-point bend specimens with deep and shallow cracks. The results show that under large scale yielding the stress and strain fields ahead of deep and shallow cracks are quite different and there is no single—parameter characteristics in these fields. Specially, the maximum hydrostatic stress is substantially lower ahead of shallow cracks than ahead of deep cracks and this strongly affects the fracture behaviour of specimens with shallow cracks. A preliminary crack length requirement for valid J—characterization of crack tip fields is suggested. The slip—line field solutions are used to develop test methods of J1C and CTOD suitable for specimens with shallow cracks as well as with deep cracks. With these methods experimental studies of fracture toughness and fracture mechanism in specimens with deep and shallow cracks for a free—cutting steel and CS 1030 plain carbon steel are carried out. The results reveal a phenomenon of ductile-brittle fracture transition due to increasing crack length in CS 1030 steel. The RKR critical stress model for cleavage fracture in conjunction with the finite element analyses of crack tip stress fields successfully explains that the ductile-brittle transition is due to the increase in the maximum tensile stress ahead of crack tip from below the critical stress to above it. The model also predicts values of CTOD of cleavage fracture in agreement with experimental results. A Rice-Johnson type model for void growth and coalescence is developed for three-point bend specimens with deep and shallow cracks and gives a qualitative explanation of the dependence of CTOD for ductile fracture on the hydrostatic stress as observed in experiment conducted in the free-cutting steel.
9
Goodwin, S. J. "A comparative study of fracture in stainless steel weld metal and wrought stainless steel." Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234832.
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10
Mohseni, Peyman. "Brittle and Ductile Fracture of X80 Arctic Steel." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19487.
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This PhD work has focused on the effect of microstructure and changes in microstructure introduced by welding procedure, on the brittle to ductile transition properties of high strength low alloy steels which have been developed for application at low temperatures (Arctic regions). For this purpose, the experimental work was based on the new pipeline steel API X80 that has a low transition temperature. The relationship between the brittle to ductile transition temperature and the microstructure in the coarse grained heat affected zone, CGHAZ, and the intercritically reheated coarse grained heat affected zone, ICCGHAZ was studied by applying Smitweld TCS1405 weld simulation for producing the HAZ microstructures. During the weld thermal cycles, both single and double cycle, the specimens were resistance heated to 1350°C by a rate of 150°C/s. The cooling rate was adjusted to give a cooling time between 800°C and 500°C (Δt8/5) of 15 seconds. The second heating cycle had a peak temperature, Tp2, of 780°C, and the cooling rate was the same as during the first cycle to simulate the reheated intercritical coarse grained HAZ. Fracture toughness was measured at low temperatures down to -90°C by both tensile and CTOD testing. In order to study the slip system activity of this steel, low cycle three point bending fatigue tests were also performed on polished specimens in the same temperature range. Fracture surfaces and changes in microstructure were analyzed by scanning and transmission electron microscopy and by light optical microscopy. In summary, the present work showed that, at each temperature the ICCGHAZ specimens had lower fracture toughness values than the CGHAZ specimens. Thus, the fracture mechanism is potentially more brittle in the case of ICCGHAZ specimens, and this is probably connected to the microstructure. The microstructure evalutions revealed that the ICCGHAZ contained blocky M-A constituents along prior austenite grain boundaries and stringer M-A constituents between the bainite laths. A more detailed investigation of the fracture surfaces by electron microscopy revealed also the existence of M-A constituents at the initiation points of the cleavage cracks. During deformation, the stress concentration is expected to increase due to the presence of the M-A constituents, and thus the level of stress and strain concentration around the M-A constituents become significantly larger than the nominal stress value and then causes initiation of cleavage fracture. Fracture surface analysis of fractured specimens documented that the cracks initiated either from debonded M-A constituents or from the region between two or more closely separated blocky M-A constituents where the transformation induced stress fields overlapped. In the present work, the initiation of cleavage fracture occurred within the double CTOD distance from the crack tip. This implies that brittle fracture is easily initiated when M-A constituents are located near the fatigue crack tip, and it is also controlled by accumulation of continuum stress fields and local plastic strains. The slip system analysis revealed that several slip systems are activated with a variety of Schmid factors within one grain, and in some cases the first activated slip system is not necessarily that with the highest Schmid factor. Thus, it can be concluded that the Schmid factor is not the only parameter that determines activation of slip. Finally, the crystallographic facet analysis by EBSD illustrated that the {100} planes are the most potent cleavage facet planes in both CGHAZ and ICCGHAZ specimens. It was also shown that the {100} and {110} planes in the case of CGHAZ, and the {100} and {211} planes in the case of ICCGHAZ were the most favourable cleavage facet planes at subzero temperatures.
11
Carroll, Martin William. "Micromechanisms of hydrogen related fracture in linepipe steel." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281960.
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12
Grundy, David C. (David Christopher). "Fatigue and fracture of a railway wheel steel." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28114.
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13
Scott, Adam James Lidstone. "Precipitation and fracture in a ferritic stainless steel." Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/10741.
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Includes bibliographical references.A dual stabilised ferritic stainless steel with titanium and niobium additions had been experiencing failures during production. Following hot rolling and cooling while coiled and prior to annealing, the steel had been prone to shattering across its width during uncoiling. This project was initiated by the manufacturers, Columbus Stainless, so that the present understanding of this stainless steel could be expanded, with the ultimate aim of avoiding production losses. This stainless steel is designed for high temperature use in automotive exhaust systems. This requires a good blend of hot strength, creep and corrosion resistance. The composition (notably the niobium addition) and manufacturing processes (where the precipitation and grain size are major concerns) are intended to provide these properties. This thesis puts the steel into the broader context of the ferritic stainless steels and discusses its high temperature use and its dual stabilisation.
14
Mai, Van Bac. "Fracture Behaviour in Cold-Reduced High-Strength Steel." Phd thesis, University of Sydney, 2019. https://hdl.handle.net/2123/29311.
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A comprehensive study on the ductile behaviour and fracture of high strength cold-reduced sheet G450 steel is presented. The aim of the study is to determine the material strength, ductility and fracture in different stress states including at both macro and structural scales. The objectives of the research are achieved through theoretical developments, extensive experimental studies and numerical investigations.
A couple damage-plasticity model derived from a generic thermodynamic framework is developed. The general formulation allows integration of stress effects (e.g. stress triaxiality and Lode angle) into the damage threshold and evolution, in addition to the ability to incorporate any form of yield criterion into the model. The key feature of the model development is that all model parameters are explicitly identified from experimental tests. In addition, the proposed model based on a combination of both plastic theory and continuum damage mechanics allows appropriately capture of the macroscopic material response.
Comprehensive experimental programmes are carried out at both the material and structural test levels where the advantages of a non-contact optical measurement (Digital Image Correlation) are successfully validated and applied. Material experiments consisting of tension and shear specimens are conducted for the determination of the material properties including fracture energy and the full-field of strain distribution and evolution. The tests of bolted connections, which are governed by block shear failure, are conducted to determine the connection strength, ductility and fracture. Strain maps in these structural tests provide an insight into the failure in the block shear limit state. In addition, all experimental data is used for determining model parameters and validating the numerical predictions.
Numerical simulation also plays an important role in this study. The proposed constitutive model is derived by an appropriate semi-implicit scheme in a general three-dimensional stress state before being incorporated into commercial numerical finite element software. All numerical predictions are validated at double scale until completion of tensile fracture consisting of macro and structural responses, which distinguishes this study from existing studies. Good predictions at the double scale show high levels of accuracy of the simulations. Further, numerical simulation of bolted connections failing in block shear serves as a supplement to experimental research and provides meaningful insight into the complex stress state. In conjunction with experimental observations, the numerical results also help to clarify the features of the recently updated block shear design equations specified in the AISI S100:2016 [1] and the AS/NZS 4600:2018 [2] standards. The proposed model has potential for further applications.Access is restricted to staff and students of the University of Sydney . UniKey credentials are required. Non university access may be obtained by visiting the University of Sydney Library.
15
Kornegay, Cynthia E. "Impact fracture of austenitic stainless steels." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/50038.
Full textAbstract:
Industry is constantly searching for improved
materials for use in highly demanding applications. The
materials chosen must withstand a wide range of
temperatures and extended exposure in aggressive
environments, including hydrogen gas. Because of the
risk of catostrophe if brittle failure occurs, careful
material selection is imperative. Austenitic stainless
steels may be a likely choice for hydrogen service
because their behavior in high pressure hydrogen ranges
from no apparent damage to relevent, but generally small
ductility loss (13). Because of this Variation in
behavior, a single category cannot be established to
encompass all austenitic steels and studies must be
performed on each type of steel to determine its behavior
under specific circumstances. Two steels being currently
under consideration for use in hydrogen are Armco 21-6-9
and Tenelon, both are fully austenitic stainless steels
which may be used over a wide range of temperatures,
including service at liquid nitrogen temperature.Master of Science
incomplete_metadata
16
Said, Mohd Noor Bin Mohd. "Effect of loading rate on the fracture toughness of structural steel weld metal." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 1989. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=59650.
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17
Johnson, David H. "Lüders bands in RPV Steel." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/8039.
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The R6 procedure is used for the prevention and prediction of crack behaviour and other defects in the reactor pressure vessel(RPV). The RPV material is an upper-bainitic, low alloy steel structure, which deforms inhomogeneously when yielding. The current codes that are used to design and calculate the fracture, within an RPV, assume that the material yields continuously as the size of the L¨uders strain is less than 2%. However, the work of Wenman et al[1] has shown that the inclusion of a L¨uders band during calculations can reduce the residual stress in a material, when compared to standard work-hardening models and, consequently, reduces the amount of conservatism. The objective of the research was to determine whether Wenman’s finding could be generalised and therefore initiate a re-evaluation of R6 procedure, when looking into materials that yield discontinuously. This required further investigation into L¨uders bands, such as using failure assessment diagrams (FADs). The findings from FADs showed that at the temperature range for an RPV steel at -155±C for different micro-structures (assuming that the material deforms homogeneously), this reduced the amount of conservatism. However, at fracture toughness values more representative of room temperature behaviour, the converse was true. That is, assuming a discontinuous yield point reduced the amount of conservatism. It was also shown that the tempered martensite structure could be used as an alternative to the current upper bainitic, low alloy steel that is used in RPVs. Further insight is gained into the nature of a L¨uders band, by developing a theoretical model that showed explicit relations between L¨uders strain and the mean free-path(ferrite path), dislocation density and the grain-size. It was also shown that an explicit relation between the L¨uders strain and carbon content was possible from known data, which a new parameter Á was derived, and is the derivative of the work-hardening exponent with respect to the lower yield stress.
18
Mahmood, K. "Influence of strain rate on oxide fracture." Thesis, Cranfield University, 1988. http://dspace.lib.cranfield.ac.uk/handle/1826/11358.
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The ability of metals and alloys to form and retain protective oxide
scales is crucial to their stability at elevated temperatures for
extended times. Hence the identification of factors that promote or
limit the integrity of oxides on high temperature materials has been the
subject of intensive investigations.
In the present study the mechanical properties of this chromiwm.-rkh
scale on 304 stainless steel foil has been investigated in relation to
the deformation rates in the substrate. It was shown that heavy cold
working (up to 90%) delays the onset of breakaway oxidation and results
in a very adherent scale.
The cracking behaviour of the scale was found to be strain rate and
temperature dependent under slow strain rate conditions when the
substrate deforms by creep. No strain rate dependence was observed over
the temperature range 700-900°C when faster strain rates (> 10-
S
sec -1)
were applied. The transition between these two responses was found to
vary only slightly with temperature between S.Ox10-
S
sec-
1
and 7.Sx10-
S
sec
-1
,increasing as the temperature is raised.
A new method has been described for determining the fracture behaviour
of oxide scale by estimating the composite defect size. From a
knowledge of the onset of scale cracking, determined in Sl(U usi ng (h~
acoustic emission technique, it was possible to correlate the measured
intercrack spacing with the fracture toughness from which the tensile
properties of the scale can be evaluated.
19
Grover, Parmeet S. "Creep-fatigue crack growth in Cr-Mo-V base material and weldments." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19540.
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20
Chang, Chung-Shing. "Fracture processes in simulated HAZ microstructures of stainless steel." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367606.
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21
Beck, R. "A ductile fracture study of A508 class 3 steel." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380067.
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22
Murrell, Pamela. "Fatigue and fracture of a high strength cast steel." Thesis, Cranfield University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359549.
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23
Ellis, M. B. D. "Fracture mechanics in a 2.25Cr-1Mo pressure vessel steel." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382220.
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24
Tong, Yangang. "Mechanisms of hydrogen-assisted fracture in low strength steel." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337233.
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25
MacLean, Christopher Glenn. "Fracture and plasticity characterization of DH-36 Navy steel." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74894.
Full textAbstract:
Thesis (Nav. E. and S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 44-47).
Multi-layered plates consisting of DH-36 steel coated by a thick layer of polyurea, for increased blast and impact protection, are of increasing importance to the Department of Defense. A hybrid approach of experiments and simulation was performed to characterize fracture and plasticity of DH-36 Navy steel, which is the first step in creating an accurate model of the composite material. The performance limit to this material during an impact is ductile fracture. The prediction follows that the onset of fracture occurs when a certain critical value of plastic strain is reached. This value is highly dependent on the state of stress. Seven different types of tests were performed, including tensile tests on dog-bone and notched specimens and punch indentation tests on circular blanks. Also, tensile and shear tests were performed on butterfly specimens using the dual actuator loading frame. Fracture surface strains were measured using digital image correlation. Local fracture strains were obtained by using an inverse engineering method of matching measured displacement to fracture with computer simulations. The results are used to calibrate the Modified Mohr Coulomb fracture model which is expressed by the stress state invariants of Lode angle and triaxiality.
by Christopher Glenn MacLean.
Nav.E.and S.M.
26
Bordet, Sylvain Richard. "Statistical micromechanical modelling of cleavage fracture in structural steel." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619642.
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27
O'Brien, Timothy John. "Ductile fracture mechanisms in carbon manganese steel weld metals." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47209.
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28
Schroth, James Gregory. "Combined mode I - mode III fracture toughness of a high-strength low-alloy steel /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260859496482.
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29
Harris, C. P. "Warm prestressing and fracture in pressure vessel steels." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383818.
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30
Rohr, Kathleen L. "Impact fracture of embrittled stainless steels." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/91149.
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Hydrogen embrittlement of austenitic stainless steels and temper embrittlement of a martensitic stainless steel have been studied by impact testing, metallography, and SEM fractography. New data for uncharged and hydrogen-charged specimens of Types 304L and 316L austenitic stainless steels show significant hydrogen effects on the impact behavior of both materials. The Type 316L specimens showed greater hydrogen effects and a more pronounced"ductile-to-brittle transition." Analysis of new and existing data for austenitic stainless steels suggests that a steel's susceptibility to hydrogen may be estimated on the basis of the magnitude of its ductile-to-brittle transition. Due to the roles played by slip planarity, transformation to martensite, and other strain rate sensitive factors, strict ordering of various steels' susceptibilities to hydrogen cannot be expected by this method. Nevertheless, the method may provide a reasonable alternative to thorough characterization of the effect of hydrogen on the mechanical properties of a given material.
The Type 416 martensitic stainless steel specimens possessed a banded ferrite/tempered martensite microstructure. Non-embrittled specimens exhibited a microvoid coalescence mode of fracture. The temper embrittlement mechanism promoted transgranular fracture of the tempered martensite phase. In the banded microstructure, ferrite/ferrite and ferrite/tempered martensite interfaces were extraordinarily weak. Their failure early in the deformation process promoted ductility by permitting relaxation of constraint on the tempered martensite phase. Tempering condition, impact data, and hardness data were correlated in order to specify a maximum acceptable hardness for a given minimum service temperature.M.S.
31
Daly, Deryck C. "Infulence [sic] of inclusions on the ductile tearing resistance of AISI 303 stainless steel." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/11186.
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32
Falk, Johannes. "Fracture prediction of stretched shear cut edges in sheets made of Dual-Phase steel." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-13956.
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Dual-Phase (DP) steels, part of the group of Advanced High Strength Steels (AHSS), are used by car manufactures due to its large strength to weight ratio. The high strength of the DP steel does have a negative impact on the formability during sheet metal forming and stretch forming, e.g. fractures often appear in shear cut edges during forming of blanks made of DP steel. The main objective with this thesis is to develop a new punch for Volvo Cars that concentrates the strain to the sheared edges of a test specimen made from different types of DP steel. This is done to be able to measure and obtain maximum fracture strain during stretch forming tests in a press. The newly developed test method is called CTEST (Concentrated Trim Edge Strain Test). The tests are performed with DP steel specimens with three different qualities of the shear cut edges; fine cut, medium cut and worn cut. DP steels tested are DP600GI, DP600UC and DP800GI from three different suppliers. 10 different types of DP steels are tested in this study with different thickness. Thickness of specimens tested are 1 mm, 1.1 mm, 1.5 mm and 2 mm and all specimens tested have a lengthwise (RD) rolling direction. The quality of the sheared cut edge has a great impact to the formability and maximum fracture strain of the specimen. A specimen with a fine cut endures higher fracture strain than medium cut and a worn cut for all types of DP steel with different thickness. A 1 mm thick specimen endures a lower fracture strain than 1.5 mm and 2 mm specimen for all cut qualities. Further, the impact of the orientation of the burr zone of a shear cut edge is studied. With the burr zone facing upwards from the CTEST punch the formability of the specimens is decreased compared to a burr zone facing downwards, especially for a worn cut specimen with micro cracks and imperfections in the edge surface. ARAMIS Digital Image Correlation (DIC) system is used to analyze the specimen edges during press experiments. The ARAMIS results unveil that several small fractures appear in the sheared edges of a specimen just before the specimens split into two pieces. This phenomenon was seen for specimen with worn and medium shear cut qualities. Finite Element (FE) simulations of the CTEST is performed in AutoForm to determine maximum values of the true strain for the three different cut qualities. The simulation in AutoForm does show a slightly higher value of the force and press depth than the value from the press test before maximum fracture strain in reached. The small fractures seen in ARAMIS just before the specimen split into two pieces cannot be seen in the simulation in AutoForm.
33
Balsara, Mukesh Narendrakumar. "Integrity assessment of flawed ductile steel pipelines." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307961.
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Jamwal, Ranbir Singh. "Microstructural origins of variability in the tensile ductility of dual phase steels." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39477.
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Quantitative relationships among processing parameters, microstructure, and material properties are of considerable interest in the context of development of robust processing routes that optimize the required material properties. As a result, the scientific literature contains a large number of experimental and theoretical studies on microstructure-properties relationships. Fracture sensitive mechanical properties such as ductility, ultimate tensile strength, fatigue life, and fracture toughness depend on the average microstructural parameters as well as the distributions of microstructural parameters and their extrema.Development of quantitative relationships between such material properties and microstructural distributions and extrema has received considerably less attention, particularly in the wrought metals and alloys. Accordingly, an important objective of this research is to perform a systematic investigation in this direction.
The dependence of the fracture-sensitive mechanical properties on the microstructural distributions and extrema often leads to substantial variability in these properties: a set of specimens having the same average chemistry, the same average processing history, and the same average microstructural parameters such as volume fractions of different constituents can exhibit substantially different material properties. The present research (i) is concerned with high strength (~ 1000 MPa) high martensite (>50%) dual phase steel where the martensite is a topologically continuous phase (matrix) containing a dispersion of islands of ferrite, and (ii) focuses on understanding the microstructural origins of the variability in fracture sensitive mechanical properties, in particular variability in the room temperature uniaxial tensile ductility. The research involves quantitative microstructure characterization using stereology and digital image processing and quantitative fractography using scanning electron microscopy (SEM) and fracture profilometry. The analysis of the quantitative fractographic and microstructural data obtained in this research leads to useful guidelines for reducing the variability in the tensile ductility of the dual phase steel under investigation.
35
Taylor, Mark. "Characterisation of normal and high-strength plain and fibre-reinforced concretes by means of strength, fracture and combined fracture/relaxation tests." Thesis, Cardiff University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365107.
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The main objective of this study was the application of strength, fracture and creep/relaxation tests to plain and fibre-reinforced high-strength concretes. Initially, five grades of concrete were developed and evaluated. Target 28 day compressive strengths were 40,60,80 100 and 120 N/mm2, the latter three being high-strength concretes (HSCs) containing a süperplasticiser and 10% silica fume. The others were normal-strength mixes used for comparison purposes. Each grade was made with 10 mm maximum-sized crushed limestone and gravel coarse aggregates making ten mixes in total. All were required to have sufficiently high workability and stability to accept reasonable amounts of fibre reinforcement. The data reported allows estimates of mix proportions for a range of HSC mixes to be determined. Various amounts of steel and polypropylene fibres were then added to the ten mixes to determine their optimum and maximum practical concentrations. The traditional type of toughness test based on un-notched beams in four-point loading was not employed. Instead, notched beams in three-point loading (equivalent to the RILEM work-of-fracture arrangement) and compact compression specimens were used. Both were tested under closed-loop conditions using crack-mouth opening displacement (CMOD) control. Post-cracking toughness was determined by means of the 15a nd 110to ughness indices given in ASTM C 1018. It was found that though fracture-based tests under CMOD control were an improvement on more traditional techniques, 15 and 110 were too insensitive to allow fibre type and volume to be differentiated. Next, work-of-fracture tests to measure the fracture energy, GF, were carried out on the plain concretes, initially under quasi-static loading. Both load/deflection and load/CMOD curves were recorded. GF showed little change with strength for a given aggregate type. Even though similar grades of crushed limestone and gravel HSCs had different GF values, the measure was still considered unsuitable for characterising the fracture properties of concrete. Similar experiments were then carried out on all ten mixes at five orders of magnitude of test duration (30 seconds to 2 days). GF appeared to be independent of strain rate. Both types of test highlighted the greater suitability of load/CMOD rather than load/deflection curves when evaluating GF. Finally, combined fracture and relaxation tests were undertaken in an attempt to obtain medium term fracture parameters. Though the CMOD was locked at 90,70 and 50% of the peak load in the strain-softening region, the deflection, when measured, showed a noticeable reduction over the seven days of each experiment, suggesting that significant cracking and stress redistribution within the fracture process zone was taking place. This finding has opened up a major area of important future research by confirming that the use of quasi-static fracture parameters in finite element studies is suspect.
36
Hill, Paul Owen. "Fatigue and fracture of the ultrahigh strength steel AerMet 100." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/4361/.
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This thesis considers the fatigue and fracture behaviour of ultra-high strength steel, AerMet 100. Two variants of AerMet 100 were tested, which had different desulphurisation and deoxidation methods. The first was desulphurised and deoxidised using mischmetal, designated MMAerMet 100. The second was desulphurised using calcium and deoxidised using titanium, designated Ca-AerMet 100. Axial fatigue testing below the 0.2% proof stress was carried out between stress ranges of 900-1700 MPa. Fractography revealed that the fatigue initiation sites could be traced to non-metallic inclusions. Samples tested in the longitudinal orientation had better fatigue lives compared to samples tested in the transverse orientation. A stress intensity factor range at the cracked inclusion at the point of initial fatigue crack growth showed a good correlation with fatigue life. Ca-AerMet 100 consistently had a better fatigue life compared to MM-AerMet 100. Fracture toughness testing showed that both variants of AerMet 100 had similar fracture toughness values and fractured by micro-void coalescence. Fractography revealed that 90% of the fracture surface was made from voids formed from secondary particles with approximate diameters of 90 nm. The work suggests that changing the desulphurisation and deoxidation method for AerMet 100 has not significantly affected the fracture toughness.
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Soberanis, Sabino Ayvar. "3D CAFE modelling of ductile fracture in gas pipeline steel." Thesis, University of Sheffield, 2007. http://etheses.whiterose.ac.uk/10310/.
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This thesis describes a series of experimental and computational studies carried out on Xl00 pipeline steel with the objective to characterise the tearing resistance of the material. A Cellular Automata-Finite Element(CAFE) technique was used in this work to develop a 3D numerical model to provide a more realistic description of the ductile damage mechanisms of the pipeline steel. In this model, the Rousselier micro-mechanisms damage theory and an appropriate cell size in a CA array represent the material behaviour. The experimental work consisted of laboratory tensile specimens in four different orientations of the material to determine the properties of the pipeline steel. Two novel designs were conducted to measure the deformation behaviour when loaded in the through wall direction. Compact C(I) and tear specimens were also tested to capture the crack growth, and the flat and shear fracture characteristics. The experimental data of laboratory samples were used to calibrate the continuum damage models. SEM (Scanning Electron Microscope) micrograph observations were carried out in tensile tests, standard C(f), slant notch C(f) and tear specimens. These observations revealed that spacing between large dimples of flat fracture are of the order of five times larger than shear fracture. It is important since the transfer of the material model parameters is made by modifying the cell size according to the average spacing between large voids in the material, d. Therefore 3D CAFE models for flat and shear fracture were created according to the microstructural characteristics to interpret the experimental findings. The main aim of the research reported here is to investigate transferability of the damage model parameters to gas pipelines steels from laboratory scale samples, and then to predict the fracture response of real structures. The CAFE technique has been shown to be a powerful tool in reducing simulation time whilst maintaining good predictions of shear damage and material resistance in terms of CTOA criterion. This was not achieved by classical FE methods where a very fine mesh is required to represent the characteristic dimension of ductile fracture. Similar reasonable results were obtained when anisotropic flat fracture was predicted but transferability of the damage parameters to CT specimens needs still further investigation.
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Do, Son Cao. "Role of residual stress relaxation in fracture of stainless steel." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680351.
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This thesis presents a study about weld residual stresses created in Esshete 1250 stainless steel cylinders and the impact of the residual stresses on fracture of the Esshete cylinders. A series of residual stress measurements in welded Esshete cylinders using both Deep Hole Drilling and incremental Deep Hole Drilling techniques are presented. These measurements are compared against independent measurements using other techniques such as Neutron Diffraction and the Contour Method on almost identical cylinders. This is to obtain a confidence on residual stress measurement results using different techniques currently available for steel. There is another stainless steel material which is studied in this thesis. That is 316L stainless steel. Residual stress measurements were also carried out on welded cylinders made of 316L material and compared with independent results. The author of this thesis carried out only the Deep Hole Drilling and incremental Deep Hole Drilling measurements. Measurement results using other techniques were obtained from other researchers such as those from the Open University. The study on the impact of the residual stresses on fracture of the welded cylinders was however done only on Esshete 1250 material. The Esshete welded cylinders were in two conditions: as-welded and thermal aged. The thermal aged condition was obtained by putting the Esshete cylinder to a furnace for 10,000 or 20,000 hours at 650°C and this is to simulate the thermal ageing effect from service at a power station. The residual stress measurements were carried out on both conditions to find out residual stress before and after thermal ageing. The conclusions were that at as-welded condition, the peak tensile value weld residual stress can exceed the yield stress of Esshete material at room temperature; repair welds increased membrane stress in weld residual stress in both axial and hoop directions; and thermal ageing relaxed significantly the weld residual stress in both girth and repair welds. The 316L cylinders are in as-welded condition only and one conclusion was that the repair weld in 316L welded cylinders also increased the membrane stress of the weld residual stress field in both axial and hoop directions. Highly tensile residual stresses were measured in a repair weld of an Esshete 1250 cylinder and motivated an investigation into how these residual stresses affect the fracture of the Esshete cylinder and how they relax with plasticity. This is because the weld residual stress has a high membrane stress of 350MPa in the axial direction and 410MPa in the hoop direction. The repair weld residual stress is found to be almost constantly tensile at 350MPa in the axial direction and 410 MPa in the hoop direction with a peak tensile stress in Esshete steel welds was found to be approximately 550MPa. The highly tensile residual stresses present in the repair welded Esshete cylinder are detrimental to the integrity of the cylinder as a crack subjected to this residual stress field is more likely to grow under external loading than if the residual stress is less tensile or the membrane component is less tensile. As a result, when an engineer accesses the structural integrity of a welded structure, tensile residual stress with a significantly tensile membrane component will require much attention and may lead to a redesign. The influence of such a highly tensile residual stress field is investigated in this thesis using Finite Element analyses. A conclusion from this study is that the repair weld residual stress has a significant effect on the fracture of the Esshete welded cylinder. The presence of tensile residual stresses were shown to promote the onset of yielding in the cracked cylinder earlier than would be the case if residual stresses were not present. However, for higher applied loads the simulations with and without residual stresses converged which indicated that the accumulated plasticity has relaxed the residual stresses completely. This is indeed a shortcoming of current structural integrity assessment codes which is the inability to predict relaxation of residual stresses with plasticity. As an example, a widely used industrial code for structural integrity assessments is R6 [1]. It is a well developed tool to predict fracture or failure of a predefined structure such as a pipe with a circumferential crack or an axial crack. It is also able to include the presence of residual stress in assessments and predict conservatively fracture or failure of a structure with the presence of residual stress. R6 is unable to predict how a residual stress field would relax with plasticity. The axial residual stress in an Esshete repair welded cylinder was also found to have similar features to a long-range residual stress field based on mapping results presented in Chapters 5 and 6. As one focus of the investigation on residual stress impact on fracture of the Esshete cylinder is how the residual stresses relax with plasticity during fracture, an idealised long-range residual stress model along with an improved experimental rig were employed to illustrate how a long-range residual stress relaxes with plasticity and the relationship of that relaxation with elastic follow-up. The long-range residual stress model and experimental rig were concluded to provide an excellent representation of how the imposed long-range residual stress relaxes with plasticity. Measured residual stress relaxation was also compared against predictions provided by the idealised model. The main part of this thesis study on residual stress impact on fracture of a welded Esshete cylinder comes from a large-scale four point bending experiment. A 600mm long Esshete steel cylinder containing a repair weld with a part-circumferential through thickness crack introduced underwent the large scale four point bending. Simulations for this four point bending experiment were carried out, with and without residual stresses. Prior to these simulation results, techniques to map measured residual stresses into 3D finite element models were developed and are explained in this thesis. The FE simulations with and without residual stresses illustrated how residual stresses influence the fracture of the long cylinder. Axial residual stress relaxation was shown using a crack affected zone concept. This concept also allows estimates of elastic follow-up created in a cracked cylinder, ,and was found to be about 1.3. This value corresponds to rapid residual stress relaxation. The relationship between the elastic follow-up of a crack affected zone with the relaxation of the axial residual stress is also discussed.
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Hou, Yuliang. "Modelling of plasticity and fracture behaviors of dual-phase steel." Thesis, Compiègne, 2016. http://www.theses.fr/2016COMP2302/document.
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L’acier à double phase (DP) a été développé par l'industrie automobile pour le but de réduire le poids, l'amélioration de la performance de la sécurité et l'efficacité énergétique. Habituellement, l'acier DP contient des îlots de martensite dure noyée dans une matrice de ferrite doux. La synergie entre ces deux phases avec la microstructure inhomogène présente d'excellentes propriétés mécaniques. Les propriétés mécaniques (comportements de plasticité et de dégâts) d'acier DP sont principalement dérivés de sa microstructure, par exemple, la fraction de volume, la taille, la distribution et la morphologie de chaque phase constituante. Les approches micromécaniques sont largement appliquées pour prédire la plasticité et d'autres propriétés mécaniques de l'acier DP selon divers scénarios de chargement. Dans ce travail, la modélisation micromécanique de l'acier DP a été réalisée en utilisant des microstructures réelles ou artificielles. Une véritable microstructure est obtenue à partir de l'image métallographique, tandis qu'un générateur de microstructure artificielle à l'aide d'un algorithme d'affectation de phase améliorée basée sur l'optimisation de la topologie matériau est proposé d'étudier les propriétés mécaniques. Dans ce générateur artificiel, un processus d'affectation de phase est réalisé sur une mosaïque de Voronoï modifié pour obtenir une mesure représentative de l'élément de volume (VER) avec une bonne convergence. La méthode proposée comprend également une réduction appropriée décomposition orthogonale (POD) des courbes de débit (instantanés), qui sont calculés en utilisant le schéma asymptotique homogénéisation d'extension (AEH), pour identifier le contrôle des paramètres optimaux pour l'acier DP. Cette méthode numérique est vérifiée en utilisant DP590 et DP980 aciers qui indiquent un bon accord avec la contrainte d'écoulement à partir de mesures et prédiction de RVE basés sur de vraies microstructures. Les prédictions des modèles de déformation plastique, y compris des bandes de cisaillement en utilisant la microstructure artificielle ressemblent étroitement le comportement mécanique réel dans des conditions de chargement similaires. En outre, une interpolation a été adoptée pour obtenir une corrélation entre ces paramètres de contrôles basés sur l'identification des différents aciers DP. En outre, un modèle de substitution bi-niveau réduit est élaboré et présenté pour identifier les paramètres matériels du critère de rupture de Mohr-Coulomb (MMC). En utilisant cette méthode, le processus d'identification devient possible avec un nombre limité de tests Expérimentaux. La méthode combine des éléments critiques locaux associés à des modèles globaux. Le modèle de substitution de la souche de fracture construit en utilisant l'approximation diffuse et les éléments locaux, réduit le coût de calcul pour la recherche des paramètres matériels. Des simulations de fracturation sont effectuées globales pour mettre à jour la déformation à la rupture de la cible et pour calculer le déplacement de l'apparition de la panne correspondante. Des résultats probants sont obtenus par application successive de la conception de l'expérience (DOE) et l'amélioration des algorithmes de transformation de l'espace de conception. Le protocole d'identification proposée est validé avec de l'acier DP590. Robustesse de la méthode est confirmée par des valeurs initiales différentes. Ces investigations numériques fournissent nouvelle direction pour les simulations multi-échelles de la plasticité et de dégâts des comportements d'acier DP. De plus, ils contribuent efficacement à combler le fossé entre la recherche scientifique et à l'application de l'ingénierie des matériaux hétérogènesDual-phase (DP) steel has been developed by automotive industry for the purpose of weight reduction, improvement in safety performance and fuel efficiency. Usually, DP steel contains hard martensite islands embedded in a soft ferrite matrix. Synergy between these two phases with the inhomogeneous microstructure exhibits excellent mechanical properties. The mechanical properties (plasticity and damage behaviors) of DP steel are mostly derived from its microstructure, e.g., volume fraction, size, distribution and morphology of each constituent phase. Micromechanical approaches are vastly applied to predict plasticity and other mechanical properties of DP steel under various loading scenarios. In this work, micromechanical modelling of DP steel has been performed using real or artificial microstructures. A real microstructure is obtained from metallographic image, while an artificial microstructure generator with an enhanced phase assignment algorithm based on material topology optimization is proposed to investigate the mechanical properties. In this artificial generator, phase assignment process is performed on a modified Voronoï tessellation to achieve the tailored representative volume element (RVE) with a good convergence. The proposed method also includes a proper orthogonal decomposition (POD) reduction of flow curves (snapshots), which are computed using the asymptotic extension homogenization (AEH) scheme, to identify the optimal controlling parameters for DP steel. This numerical method is verified using DP590 and DP980 steels that indicate a good agreement with the flow stress from measurements and RVE prediction based on real microstructures. Predictions of plastic strain patterns including shear bands using the artificial microstructure closely resemble the actual mechanical behavior under similar loading conditions. Moreover, an interpolation has been adopted to obtain a correlation between these controlling parameters based on the identification for various DP steels. Additionally, a bi-level reduced surrogate model is developed and presented to identify the material parameters of the Mohr-Coulomb (MMC) fracture criterion. Using this method, the identification process becomes feasible with a limited number of experimental tests. The method combines local critical elements associated with global models. The surrogate model of fracture strain constructed using the diffuse approximation and the local elements, reduced the computational cost for searching material parameters. Global fracture simulations are performed to update the target fracture strain and to compute the corresponding failure onset displacement. Convincing results are obtained via successive application of design of experiment (DOE) and enhanced design space transformation algorithms. The proposed identification protocol is validated with DP590 steel. Robustness of the method is confirmed with different initial values. These numerical investigations provide new direction for multiscale simulations of the plasticity and damage behaviors of DP steel. Moreover, they efficiently contribute to bridge the gap between scientific research and engineering application of heterogeneous materials
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Joenoes, Ahmad T. "Quantitative analysis of fatigue behavior, fatigue damage and fatigue fracture surfaces of low carbon bainitic steel (SAE 15B13)." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19671.
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Jones, M. R. "The mechanisms of ductile fracture in pressure vessel steels." Thesis, Open University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377915.
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The micromechanisms by which ductile fracture extended from a pre-existing crack was experimentally observed for two classes of forged SA 508 pressure vessel steel. The micromechanisms were related to the measured values of fracture toughness characterised by the resistance to crack initiation and growth. This comparison was only possible with the aid of an accurate fracture resistance test technique which could determine the crack growth toughness from a single specimen. An unloading compliance test system was developed and was used for the construction of crack growth resistance curves. Microstructural parameters determined from a specimen were related to the toughness measured on that specimen and this proved invaluable in isolating the controlling parameters. The effect of orientation and location on the toughness of the materials was assessed. The crack growth resistance was sensitive to the orientation of the crack with respect to the maximum hot working direction and the bands of segregation associated with elongated manganese sulphide inclusions. The toughness was high when the crack plane was perpendicular to the segregation bands and low when the crack plane was parallel with the bands. The location of the crack-tip through the thickness of the forging had a minor effect on the crack growth resistance. A limited study of test temperature, strength level and isothermal ageing was undertaken. Testing within the dynamic strain ageing regime of temperature had a marked effect and reduced the crack growth resistance to below the value at room temperature. Increasing the strength level of one steel by re-heat treating had no effect on the crack growth resistance. Subsequent isothermal ageing treatments also had no effect on the resistance curves. The magnitude and extent of void formation around growing cracks was studied and related to the applied loading. The size, shape and distribution of inclusions was characterised for the materials and orientations used in the fracture tests. Correlations between inclusion parameters and toughness revealed the important microstructural parameters controlling initiation and crack growth. Simple models for initiation and crack growth resistance were developed which take the controlling parameters into account. These models are shown to agree reasonably well with some experimental data.
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Abdul-Salam, Ezzet Hameed. "Fatigue crack propagation in mild steel." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291749.
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Damri, Daniel. "Transient fatigue crack growth in a structural steel." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386012.
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Mazinani, Mohammad. "Deformation and fracture behaviour of a low-carbon dual-phase steel." Thesis, University of British Columbia, 2006. http://hdl.handle.net/2429/30951.
Full textAbstract:
The primary goal of this study was to evaluate the effect of martensite plasticity on the
deformation and fracture behaviour of an intercritically annealed commercial low carbon (0.06
wt.%) dual phase steel. The volume fraction and the morphology (banded and almost equiaxed)
of the martensite phase were systematically varied by control of the intercritical annealing
temperature and the heating rate to this temperature. It was observed that the yield and tensile
strengths were dependent on the martensite content but not on the martensite morphology. On
the other hand, the true uniform strain, fracture strain and fracture stress were found to have a
significant dependence on martensite morphology.
An Eshelby based model, which allowed for the calculation of the stress in the martensite
islands, was employed in order to rationalize the tensile properties of the dual-phase steel
samples with different martensite contents and morphologies. In addition, by comparing the
calculated stress in the martensite with an estimate of yield stress, it was possible to examine
the conditions under which martensite plasticity occurs. The work hardening behaviour and the
fracture properties of the steel samples were rationalized by the implications of martensite
plasticity. For the cases where martensite showed significant plasticity (or co-deformed with
the ferrite matrix), the void nucleation rate during post-necking deformation decreased
considerably and hence, the final fracture properties were dramatically improved.
The deformation of martensite in different dual-phase steel samples was examined both
qualitatively (using optical micrographs of the undeformed and deformed sections of fractured tensile samples) and quantitatively (through image analysis of the microstructures before and
after tensile deformation). The tensile stress-strain responses of different dual-phase steel
samples were modeled using the modified Eshelby method. This approach was found
appropriate for modelling the stress-strain behaviour of the steels with equiaxed morphology
and martensite contents below approximately 30%. In the case of banded morphology, the
stress-strain behaviour of the steel sample with 17% martensite was successfully predicted by
the model. However, the model overestimated the flow stress of the steel with 30% martensite.
For the martensite contents greater than 30%, the overestimation of the flow stress of the steel
samples with banded morphology was greater than that for the equiaxed samples.
Finally, the void formation process during tensile deformation was examined quantitatively
through image analysis of the fracture surface of the steels. The experimental results showed
very little void growth during ductile fracture of the steel samples with 17% and 41%
martensite. Modelling the void formation process in these steels assuming no void growth stage
resulted in the same observation. This confirmed the quantitative observation that void
nucleation is the dominant effect during ductile fracture of these steels.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Sharma, Samit. "Fracture crack relative to weld interface in a pressure vessel steel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0014/MQ35852.pdf.
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Sorbello, Fabio. "Role of interfaces on the fracture resistance of iron-silicon steel." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492598.
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Gruben, Gaute. "Ductile Fracture in Dual-Phase Steel : Theoretical, Experimental and Numerical Study." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19445.
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The thesis is focused on quasi-static ductile fracture in the low range of stress triaxiality of the dual-phase steel Docol 600DL. The study includes mechanical testing, theoretical aspects of ductile fracture and numerical simulations. Ductile fracture in the low range of stress triaxiality is an interesting topic since experimental data from various studies suggests that the ductility of the material is not only governed by the hydrostatic stressstate, but is also influenced by the deviatoric stress-state. The thesis consists of four journal articles bound together by a synopsis, where the introduction gives the motivation for the work and a state-of-the-art of the topics examined in this study. After the introduction, the objectives for the study are given followed by a summary of the work, conclusions and suggestions for further work. Finally the four articles are given. The articles are referred to as parts as they give detailed information of the different parts of the study. In Part I and Part II the experimental side of the study is described. These parts give detailed information regarding the material, test set-ups, specimen geometries and optical measurement procedures. The results from the experiments in form of the minor versus major principal strain as well as the stress triaxiality, the Lode parameter, and the equivalent strain at fracture are presented and used to describe the material’s fracture characteristics. Macroscopically the material displayed typical ductile behaviour with large strains before fracture. This was confirmed by scanning electron microscopy of selected specimens since all showed ductile dimples. Further, the material displayed a significant drop in ductility when exposed to plane-strain loading; an observation that suggests that the material’s fracture properties are Lode dependent. In Part III several uncoupled criteria for ductile fracture which explicitly take into account the effect of the Lode dependence were assessed. One of the criteria, the modified Mohr-Coulomb criterion, was taken from literature, while two of the criteria, the extended Cockcroft-Latham criterion and the extended Rice-Tracey criterion are augmented versions of existing criteria. The data given in Part I and II were used in evaluating the various criteria and it was found that the proposed extended Cockcroft- Latham criterion managed to give accurate predictions on the equivalent strain at fracture, while a somewhat larger spread was observed for the modified Mohr-Coulomb criterion and the extended Rice-Tracey criterion. Part IV focuses on numerical modelling of ductile crack propagation. Here the experimental tests from Part I were used in assessing the extended Cockcroft-Latham and modified Mohr-Coulomb criteria on crack propagation. Additionally the effects of using a high-exponent yield surface and material softening were investigated. It was found that the different fracture criteria as well as a change of yield function had little effect on the crack propagation. By including material softening through damage coupling, slant shear fracture as observed in some of the experiments was captured, but this did not alter the global response in form of the force-displacement curves.
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Wang, Li. "Ductile fracture simulation of structural steel using the local approach method." Thesis, University of the West of England, Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271053.
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Neville, D. J. "Statistical aspects of brittle fracture in homogeneous and inhomogeneous steel microstructures." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355274.
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Roddis, W. M. Kim. "Heuristic, qualitative, and quantitative reasoning about steel bridge fatigue and fracture." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/69700.
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