Artykuły w czasopismach: „Open Hole Tensile Testing”

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Sanei, Seyed HR, Andrew Arndt i Randall Doles. "Open hole tensile testing of 3D printed continuous carbon fiber reinforced composites". Journal of Composite Materials 54, nr 20 (23.01.2020): 2687–95. http://dx.doi.org/10.1177/0021998320902510.

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In this study, the effects of stress concentration on the tensile properties of a 3D printed carbon fiber-nylon composite were investigated. The samples were 3D printed with continuous carbon fiber and chopped fiber reinforced nylon. Samples were manufactured with four different open hole sizes as 3. 175 mm (⅛ in), 6.35 mm (¼ in), 9.25 mm (⅜ in), and 12.7 mm (½ in). Five samples were manufactured for each hole size group. Continuous carbon fibers were printed in the longitudinal direction. Additional reinforcements were placed around the periphery of the open hole. Samples were tested under uniaxial tension. The results were compared with the prediction of fracture mechanics theories namely Average and Point Stress Criteria. The results show that failure was initiated at the stress concentration region but the progression into the hole was prevented with the presence of continuous fiber. The experimental findings show that the samples with larger holes are more sensitive to discontinuity than the ones with smaller holes. The results confirm that 3D printing can be used to strengthen the parts at the discontinuity region to mitigate the effect of stress concentration.

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Bale, J. "Damage Behaviour and Stress Concentration Factor of Open Hole Tensile (OHT) Glass Fibre Reinforced Polymer (GFRP) Composites". International Journal of Automotive and Mechanical Engineering 16, nr 4 (30.12.2019): 7299–314. http://dx.doi.org/10.15282/ijame.16.4.2019.09.0543.

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In many applications of composites, open-hole frequently includes for various purposes. However, further study on open-hole behaviour is still required, including on its strength and damage properties by combining experimental testing, real-time observations and calculations based on theoretical analysis and simulation model. The objective of this study is to understand the effect of an open-hole glass fibre reinforced polymer (GFRP) composites on tensile (static) properties, damage behaviour through Non-destructive Testing (NDT) Thermography and stress concentration factor (SCF). This study used an open-hole rectangular of GFRP specimens that fabricated by filament winding (FW) method and resin transfer moulding (RTM) method. It is found that the RTM specimens generate ≈ 170 % higher of tensile strength and ≈ 100 % higher of tensile modulus compared to the FW specimens. Infra-red (IR) camera shown the good detection on damage behaviour based on temperature increase at elastic and failure phase. Moreover, theoretical analysis and simulation results shown the good correlation where SCF reaches more than 4 times at the edge of the hole. This study concludes that open-hole on GFRP composites affects the tensile properties and generates damage marked by temperature increase and high SCF at the edge of the hole.

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Dave, Harshit K., Ashish R. Prajapati, Shilpesh R. Rajpurohit, Naushil H. Patadiya i Harit K. Raval. "Open hole tensile testing of 3D printed parts using in-house fabricated PLA filament". Rapid Prototyping Journal 26, nr 1 (6.01.2020): 21–31. http://dx.doi.org/10.1108/rpj-01-2019-0003.

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Purpose Fused deposition modeling (FDM) is being increasingly used in automotive and aerospace industries because of its ability to produce specimens having difficult geometrical shape. However, owing to lack of critical information regarding the reliability and mechanical properties of FDM-printed parts at various designs, the use of 3D printed parts in these industries is limited. Therefore, the purpose of this paper is to investigate the impact of process parameters of FDM on the tensile strength of open-hole specimen printed using in-house-fabricated polylactic acid (PLA). Design/methodology/approach In the present study, three process parameters, namely, raster angle, layer thickness and raster width, are selected for investigation of tensile strength. To produce the tensile specimens in the FDM machine, the PLA filament is used which is fabricated from PLA granules using a single-screw extruder. Further, the experimental values are measured and critically analysed. Failure modes under tests are studied using scanning electron microscopy (SEM). Findings Results indicate that the raster angle has a significant effect on the tensile strength of open-hole tensile specimen. Specimens built with 0° raster angle, 200-µm layer thickness and 500-µm raster width obtained maximum tensile strength. Originality/value In this work, a new concept of testing a plate that has a rectangular shape and a circular hole at the centre is tested. Open-hole tensile test standard ASTM D5766 has been implemented for the first time for the FDM process.

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Zhang, Xiao Qiong, Wei Guo Guo i De Shuan Kong. "Damage Analysis of 2D Woven Composite Laminates Containing an Open-Hole under Tensile Loadings". Key Engineering Materials 525-526 (listopad 2012): 373–76. http://dx.doi.org/10.4028/www.scientific.net/kem.525-526.373.

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In order to understand damage mechanism, the influences of lay-up construction of laminates and environgment on tension behavior of 2D woven composite laminates with an open-hole, which was manufactured by a new technology, uniaxial tension tests are performed in 3 different environments on 4 kinds of lay-up specimens, using a WE-50 electromechanical universal material testing machines. The fracture of specimens are analysed through micrographic observations. The result show that there is a large difference both in tensile strength and damage mechanism due to different kinds of lay-up specimens: 1) the tensile strength of specimens that only with ±45 degree laminated is much lower than other samples with different kinds of layup and its tensile stress-strain curves presents nonlinear; 2)The failure modes and damage mechanism determines the strength of specimens; 3)The change of environment had a certain effect on the mechanical behaviors of materials, in this paper, it will cause the tensile strength of speicmens decreasing.

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Strungar, Elena, Dmitrii Lobanov i Valery Wildemann. "Evaluation of the Sensitivity of Various Reinforcement Patterns for Structural Carbon Fibers to Open Holes during Tensile Tests". Polymers 13, nr 24 (7.12.2021): 4287. http://dx.doi.org/10.3390/polym13244287.

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This paper is devoted to the experimental study of polymeric composite specimens, with various types of reinforcement, in order to evaluate the breaking strength of specimens with open holes when undergoing uniaxial compression and tensile tests. Four types of interlaced 3D woven preforms were considered (orthogonal, orthogonal combined, with pairwise inter-layer reinforcement, and with pairwise inter-layer reinforcement and a longitudinal layer), with a layered preform used for comparison. Tensile tests of solid specimens without a hole, under ASTM D 3039, and of specimens with an open hole, under ASTM D 5766, were carried out using the Instron 5989 universal electromechanical testing system. Movements and strains on the specimen surface were recorded using a Vic-3D contactless optical video system and the digital images correlation method (DIC). For all the series of carbon fiber tension specimens, strain and stress diagrams, mechanical characteristics, and statistical processing for 10 specimens were obtained. The paper evaluated deformation fields for certain points in time; the obtained fields showed an irregular distribution of deformation and dependency on types of reinforcing fibers. A coefficient of strength variation is introduced, which is defined as a ratio of the ultimate stress limits obtained on solid samples with and without open holes. Within the framework of ASTM D 5766, when calculating the ultimate stress, the hole is not taken into account, and the paper shows that for certain structures a hole cannot be excluded. The hole size must not be neglected when calculating the ultimate stress.

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Hallett, Stephen R., Ben G. Green, Wen-Guang Jiang, Kin Hei Cheung i Michael R. Wisnom. "The open hole tensile test: a challenge for virtual testing of composites". International Journal of Fracture 158, nr 2 (19.03.2009): 169–81. http://dx.doi.org/10.1007/s10704-009-9333-8.

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Bale, Jefri, Emmanuel Valot, Martine Monin, Olivier Polit, Claude Bathias i Tresna Soemardi. "Tomography Observation of Fiber Reinforced Composites after Fatigue Testing". Applied Mechanics and Materials 799-800 (październik 2015): 937–41. http://dx.doi.org/10.4028/www.scientific.net/amm.799-800.937.

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This work presented an experimental study to observe the inside conditions and damage appearances of fiber reinforced composites material by non destructive testing (NDT) method. In order to achieve this, an open hole specimen of unidirectional glass fiber composite (GFRP) and discontinuous carbon fiber composite (DCFC) had been using as the specimen test under tensile fatigue loading and observed using post failure monitoring techniques of NDT namely computed tomography (CT) scan. The results shown that the tomography observation based on segmentation method of gray value gives a good detection on early damage appearances before final failure of GFRP and DCFC after tensile fatigue loading conditions.

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Iragi, M., C. Pascual-González, A. Esnaola, U. Morales, J. Aurrekoetxea, C. S. Lopes i L. Aretxabaleta. "Design, manufacturing and testing of 3D printed variable-stiffness laminates for improved open-hole tensile behaviour". Additive Manufacturing 63 (luty 2023): 103418. http://dx.doi.org/10.1016/j.addma.2023.103418.

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Bale, Jefri, Emmanuel Valot, Martine Monin, Peggy Laloue, Olivier Polit, Claude Bathias i Tresna Priyana Soemardi. "Damage Observation of Glass Fiber/Epoxy Composites Using Thermography and Supported by Acoustic Emission". Applied Mechanics and Materials 627 (wrzesień 2014): 187–90. http://dx.doi.org/10.4028/www.scientific.net/amm.627.187.

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This work presents an experimental study to monitor the damage propagation of composite material by non destructive testing (NDT) method. In order to achieve this, an open hole condition of glass fiber/epoxy composite has been used as the specimen test under static tensile loading and observed using two different real-time monitoring techniques of NDT namely infra-red (IR) camera and supported by Acoustic Emission. The results show that the thermal response and acoustic emission signals give a good detection on damage appearance and damage propagation of glass fiber/epoxy composite under static tensile loading conditions.

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Farrow, I. R., J. Lee i C. D. Kong. "Flexural Testing of Composite Laminates for Drilling Trial Assessment". Advanced Composites Letters 9, nr 4 (lipiec 2000): 096369350000900. http://dx.doi.org/10.1177/096369350000900403.

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This work presents a study of flexural testing as a convenient method for ranking drilling trials of composite materials. The work includes an experimental study of drilling parameter effects on composite laminate hole quality as measured by static tension, compression and flexural open hole tests. Flexural testing and results processed in terms of the outermost 0° layer provides a consistent ranking of holes drilled with different process parameters despite only subtle changes in static notched strength for the thick composite samples tested. Specific observations from flexural tests are consistent with current drilling practices in terms of best process parameter settings and the method shows sufficient sensitivity to distinguish between the effects of drill-entry and drill-exit damage and subtle changes in lay-up.

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Elbadry, Elsayed A., GA Abdalla, M. Aboraia i EA Oraby. "Notch sensitivity of short and 2D plain woven glass fibres reinforced with different polymer matrix composites". Journal of Reinforced Plastics and Composites 36, nr 15 (7.04.2017): 1092–98. http://dx.doi.org/10.1177/0731684417702529.

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This research article investigated the notch sensitivity of two different glass fibre architectures, namely short and 2D plain-woven glass fibres reinforced with unsaturated polyester and epoxy matrix composites fabricated by the hand lay-up technique. This was carried out through open hole tension tests at different ratios of the specimen hole diameter to the specimen with three different values (0.1, 0.2, 0.5) compared to the unnotched specimen. The notch sensitivity of these composites was evaluated using the residual tensile strength by the application of Whitney–Nuismer Mathematical Model. The results showed that by using polyester matrix, the notch sensitivity of composites reinforced with plain-woven glass fibre is higher than that of short glass fibre at different D/W ratios. On the other hand, on testing epoxy matrixes, the notch sensitivity of composites reinforced with plain-woven glass fibre is lower than that of short glass fibre at different D/W ratios.

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Jiang, Xiao-Wei, Hai Wang i Shijun Guo. "Peridynamic Open-Hole Tensile Strength Prediction of Fiber-Reinforced Composite Laminate Using Energy-Based Failure Criteria". Advances in Materials Science and Engineering 2019 (20.01.2019): 1–14. http://dx.doi.org/10.1155/2019/7694081.

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In the present study, peridynamic (PD) open-hole tensile (OHT) strength prediction of fiber-reinforced composite laminate using energy-based failure criteria is conducted. Spherical-horizon peridynamic laminate theory (PDLT) model is used. Energy-based failure criteria are introduced into the model. Delamination fracture modes can be distinguished in the present energy-based failure criteria. Three OHT testing results of fiber-reinforced composite laminate are chosen from literatures and used as benchmarks to validate the present PD composite model with energy-based failure criteria. It is shown that the PD predicted OHT strength fits the experimental results quite well. From the predicted displacement field, the fracture surface can be clearly detected. Typical damage modes of composite, fiber breakage, matrix crack, and delamination, are also illustrated in detail for each specimen. Numerical results in the present study validate the accuracy and reliability of the present PD composite model with energy-based failure criteria.

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Seon, Guillaume, Andrew Makeev, Joseph D. Schaefer i Brian Justusson. "Measurement of Interlaminar Tensile Strength and Elastic Properties of Composites Using Open-Hole Compression Testing and Digital Image Correlation". Applied Sciences 9, nr 13 (29.06.2019): 2647. http://dx.doi.org/10.3390/app9132647.

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Advanced polymeric composites are increasingly used in high-performance aircraft structures to reduce weight and improve efficiency. However, a major challenge delaying the implementation of the advanced composites is the lack of accurate methods for material characterization. Accurate measurement of three-dimensional mechanical properties of composites, stress–strain response, strength, fatigue, and toughness properties, is essential in the development of validated analysis techniques accelerating design and certification of composite structures. In particular, accurate measurement of the through-thickness constitutive properties and interlaminar tensile (ILT) strength is needed to capture delamination failure, which is one of the primary failure modes in composite aircraft structures. A major technical challenge to accurate measurement of ILT properties is their strong sensitivity to manufacturing defects that often leads to unacceptable scatter in standard test results. Unacceptable failure mode in standard test methods is another common obstacle to accurate ILT strength measurement. Characterization methods based on non-contact full-field measurement of deformation have emerged as attractive alternative techniques allowing more flexibility in test configuration to address some of the limitations inherent to strain gauge-based standard testing. In this work, a method based on full-field digital image correlation (DIC) measurement of surface deformation in unidirectional open-hole compression (OHC) specimens is proposed and investigated as a viable alternative to assessing ILT stress–strain, strength, and fatigue properties. Inverse identification using a finite element model updating (FEMU) method is used for simultaneous measurement of through-thickness elastic constants with recovery of the maximum ILT stress at failure for characterization of strength and fatigue S–N curves.

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Stock, Johannes W., i Johanna Kerschreiter. "Modelling the Stress Concentration in CFRP at Notches with a Thermally Influenced Cut Edge". Advanced Materials Research 1140 (sierpień 2016): 288–95. http://dx.doi.org/10.4028/www.scientific.net/amr.1140.288.

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The use of higher laser powers in laser cutting of CFRP results in both an increase of productivity and in a growth of the heat affected zone at the cut edge. This thermal damage was related to a loss of the static strength due to the reduce load bearing cross section in various studies. In contrast, the thermal damage caused an increase of the average number of load cycles and to a significant reduction of the deviation among the repetitions of each parameter during dynamic open hole tensile testing in recent studies. To explain this positive influence of laser cutting on the fatigue behaviour of CFRP, an analytical model of the load concentration in a plate with a circular notch could be adapted and modified. The orthotropic property of the material is considered in the model. The static strength of thermally treated CFRP was determined in experiments and applied to the model. By inserting the measured temperature-dependent values of the Young´s modulus, the critical tension at the notch could be determined related to the dimensions of the heat affected zone.

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Dall’Asta, E., V. Ghizzardi, R. Brighenti, E. Romeo, R. Roncella i A. Spagnoli. "New experimental techniques for fracture testing of highly deformable materials". Frattura ed Integrità Strutturale 10, nr 35 (29.12.2015): 161–71. http://dx.doi.org/10.3221/igf-esis.35.19.

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A new experimental method for measuring strain fields in highly deformable materials has been developed. This technique is based on an in-house developed Digital Image Correlation (DIC) system capable of accurately capturing localized or non-uniform strain distributions. Thanks to the implemented algorithm based on a Semi-Global Matching (SGM) approach, it is possible to constraint the regularity of the displacement field in order to significantly improve the reliability of the evaluated strains, especially in highly deformable materials. Being originally introduced for Digital Surface Modelling from stereo pairs, SGM is conceived for performing a one-dimensional search of displacements between images, but here a novel implementation for 2D displacement solution space is introduced. SGM approach is compared with the previously in-house developed implementation based on a local Least Squares Matching (LSM) approach. A comparison with the open source code Ncorr and with some FEM results is also presented. The investigation using the present DIC method focuses on 2D full-field strain maps of plain and notched specimens under tensile loading made of two different highly deformable materials: hot mix asphalt and thermoplastic composites for 3D-printing applications. In the latter specimens, an elliptical hole is introduced to assess the potentiality of the method in experimentally capturing high strain gradients in mixed-mode fracture situations.

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Clay, Stephen B., i Philip M. Knoth. "Experimental results of quasi-static testing for calibration and validation of composite progressive damage analysis methods". Journal of Composite Materials 51, nr 10 (15.07.2016): 1333–53. http://dx.doi.org/10.1177/0021998316658539.

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The Air Force Research Laboratory directed a research program to evaluate nine different composite progressive damage analysis methods under both quasi-static and fatigue loading. This paper describes the coupon tests that were performed at the Air Force Research Laboratory for calibration and validation of the methods under quasi-static conditions. The basic elastic and failure properties of unidirectional IM7/977-3 graphite/epoxy were first determined in order to properly calibrate the models. Validation tests were then performed on unnotched and open-hole coupons with three different laminate stacking sequences under both tension and compression loading conditions. This paper summarizes these experimental results and provides X-ray computed tomography images at subcritical load levels.

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Nobile, R., F. W. Panella, A. Pirinu i A. Saponaro. "Full-field monitoring methods for damage analysis on aeronautical CFRP specimens under fatigue loads". IOP Conference Series: Materials Science and Engineering 1214, nr 1 (1.01.2022): 012008. http://dx.doi.org/10.1088/1757-899x/1214/1/012008.

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Abstract The present paper is focused on full-field experimental monitoring procedures to be employed during HCF fatigue testing on two series of CFRP open hole samples. Two different experimental methodologies based on thermographic techniques and displacement measurements with Digital Image Correlation (DIC) analysis are employed for damage settlement and evolution to be detected up to failure, together with correspondent compliance analysis. Combined monitoring approaches, based on thermo-elastic and dissipative phenomena, together with stiffness properties variations, are claimed to offer precise damage state localization during tests in real time; in addition, DIC analysis is performed during low-frequency fatigue cycle is studied for better failure prediction and damage location. The thermal parameters and experimental compliance correlation seem to indicate similar signal variation during damage progress and after proper data elaboration; contemporaneous raw thermal measurements in critical zones of specimens under fatigue life offer a kind of delamination recognition at specific layer interface and location, as well as propagation before final failure. Sample under tensile load on the other hand reveal delaminations indirectly on the surface. In addition, non-destructive thermographic and ultrasound tests are performed at regular intervals during fatigue life.

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Chen, Jian, Xiongfei Li, Wei Li, Cong Li, Baoshan Xie, Shuowei Dai, Jian-Jun He i Yanjie Ren. "Research on energy absorption properties of open-cell copper foam for current collector of Li-ions". Materials Science-Poland 37, nr 1 (1.03.2019): 8–15. http://dx.doi.org/10.2478/msp-2019-0011.

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AbstractQuasi-static uniaxial compressive tests of open-cell copper (Cu) foams (OCCF) were carried out on an in-situ bi-direction tension/compress testing machine (IBTC 2000). The effects of strain rate, porosity and pore size on the energy absorption of open-cell copper foams were investigated to reveal the energy absorption mechanism. The results show that three performance parameters of open-cell copper foams (OCCF), involving compressive strength, Young modulus and yield stress, increase simultaneously with an increase of strain rate and reduce with increasing porosity and pore size. Furthermore, the energy absorption capacity of OCCF increases with an increase of porosity and pore size. However, energy absorption efficiency increases with increasing porosity and decreasing pore size. The finite element simulation results show that the two-dimensional stochastic model can predict the energy absorption performance of the foam during the compressive process. The large permanent plastic deformation at the weak edge hole is the main factor that affects the energy absorption.

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Builes Cárdenas, Cristian, Vincent Gayraud, Maria Eugenia Rodriguez, Josep Costa, Asier M. Salaberria, Alaitz Ruiz de Luzuriaga, Nerea Markaide, Priya Dasan Keeryadath i Diego Calderón Zapatería. "Study into the Mechanical Properties of a New Aeronautic-Grade Epoxy-Based Carbon-Fiber-Reinforced Vitrimer". Polymers 14, nr 6 (17.03.2022): 1223. http://dx.doi.org/10.3390/polym14061223.

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The current drive for sustainability demands recyclable matrices for composite materials. Vitrimers combine thermoset properties with reprocessability, but their mechanical performance in highly loaded applications, for instance, composites for aeronautics, is still to be demonstrated. This work presents the complete mechanical characterization of a new vitrimer reinforced with carbon fiber. This vitrimer formulation consists of functional epoxy groups and a new dynamic disulfide crosslinks-based hardener. The testing campaign for the vitrimer composites encompassed tension, compression, interlaminar shear strength (ILSS), in-plane shear (IPS), open-hole tension (OHT) and compression (OHC), filled-hole compression (FHC) and interlaminar fracture toughness tests under mode I and II. Test conditions included room temperature and high temperature of 70 °C and 120 °C, respectively, after moisture saturation. Tension and flexural tests also were applied on the neat vitrimer resin. The results compared well with those obtained for current aeronautic materials manufactured by Resin Transfer Molding (RTM). The lower values observed in compression and ILSS derived from the thermoplastic veils included as a toughening material. This work demonstrates that the vitrimer formulation presented meets the requirements of current matrices for aeronautic-grade carbon-reinforced composites.

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Clay, Stephen B., i Philip M. Knoth. "Experimental results of fatigue testing for calibration and validation of composite progressive damage analysis methods". Journal of Composite Materials 51, nr 15 (16.09.2016): 2083–100. http://dx.doi.org/10.1177/0021998316670132.

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The Air Force Research Laboratory led a research effort to benchmark the accuracy of static and fatigue predictions of several emerging composite progressive damage analysis techniques. The static portion of this technical effort is described in detail in a previous special issue of the Journal of Composite Materials. This paper provides the details of the fatigue experiments that were conducted to calibrate and validate the computational models. Initially, in-plane and out-of-plane S–N curves were generated through coupon tests that were performed on unidirectional laminae. The challenges experienced during fatigue testing of in-plane, matrix-dominated unidirectional coupon specimens are presented in detail. The higher fidelity test data from the fiber-dominated and out-of-plane experiments are also included in this paper. Following the calibration experiments, a series of tension–tension fatigue validation tests were conducted on open-hole coupons with three different stacking sequences. Each specimen was cycled to a pre-determined number of fatigue cycles, followed by static residual strength tests in both tension and compression. This paper provides the stress–strain responses of these validation tests as well as high-resolution X-ray computed tomography images of the subsurface damage as a function of cycles. Seven analysis teams used these test results to calibrate their models and to benchmark the accuracy of their predictions of damage and residual mechanical properties.

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Steinbach, Frank, Alper Güner i A. Erman Tekkaya. "Dry Shearing of Micro-Alloyed Steels". Key Engineering Materials 622-623 (wrzesień 2014): 1058–65. http://dx.doi.org/10.4028/www.scientific.net/kem.622-623.1058.

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In the production process of sheet metal parts, oil is widely used as lubricant, not only in sheet metal forming but also in shearing and blanking. Due to environment, health and cost reasons, the absence of lubricants is an aim for future production as it has initiated for machining in the last years. For lubricant-free shearing, it has to be known if there is an influence on the process itself when using oil or not. To find this out, experiments are carried out with a small testing device installed in a tensile testing machine and a blanking tool installed in a servo press. With the small device it is possible to make a piercing process with a circle punch of 16 mm diameter. The blanking tool produces a larger cut part with different holes and open cuts. Without lubricant, there is no difference in the maximum shearing force for the small device while the stripping force is higher and the cut edge zones differs slightly. Using oil or not has a small effect on the force using the blanking tool.

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Mára, Vladimír, Jan Krčil, Lenka Michalcová i Elena Čižmárová. "The Failure of Carbon Fiber Reinforced Composite Analyzed by Acoustic Emission". Defect and Diffusion Forum 405 (listopad 2020): 205–11. http://dx.doi.org/10.4028/www.scientific.net/ddf.405.205.

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This paper focus on evaluation of behavior, damage and failure processes occurring during the loading cycles in the carbon fiber reinforced composite by acoustic emission method. Since acoustic emission is physical phenomenon that detects the released energy in form of waves spreading through the material due to stimulation of material by external or internal stress, it is possible to evaluate complex damage and failure processes. For that purpose, the standard and open holes tensile testing specimens with different number of plies were manufactured. Selected acoustic emission parameters were correlated with data obtained from mechanical test. Linear localization method together with signal analysis using Fast Fourier transform algorithm were used as another tool for detection and evaluation of spreading damage processes inside the composite during the load. Basic damage types inside the composite material were identified by metallographic analysis using light microscopy. More complex damage processes were observed on the fracture surface using stereomicroscopy and scanning electron microscopy.

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DorMohammdi, Saber, Cody Godines, Frank Abdi, Dade Huang, Massimiliano Repupilli i Levon Minnetyan. "Damage-tolerant composite design principles for aircraft components under fatigue service loading using multi-scale progressive failure analysis". Journal of Composite Materials 51, nr 15 (20.03.2017): 2181–202. http://dx.doi.org/10.1177/0021998317691812.

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Virtual testing has lately gained widespread acceptance among scientists as a simple, accurate, and reproducible method to determine the mechanical properties of heterogeneous microstructures, early in the production process. As a result of the rapid expansion of the use of composites in aerospace design, virtual testing techniques are, in fact, deemed extremely useful to eliminate unnecessary tests and to reduce cost and time associated with generating allowables for lengthy lifing analyses of structures. Leveraging on a limited set of experimental data, a Progressive Failure Analysis can accurately predict the life and safety of a component/assembly, simply tapping on the physics of its micro-/macro- mechanics material properties, manufacturing processes, and service environments. The robust methodology is showcased using blind predictions of fatigue stiffness degradation and residual strength in tension and compression after fatigue compared with test data from Lockheed Martin Aeronautics and Air Force Research Laboratory). The multi-scale progressive failure analysis methodology in the GENOA software considers uncertainties and defects and evaluated the damage and fracture evolution of three IM7-977-3 laminated composite layups at room temperature. The onset and growth of composite damage was predicted and compared with X-ray CT. After blind predictions, recalibrations were performed with knowledge of the test data using the same set of inputs for all layups and simulations. Damage and fracture mechanism evolution/tracking throughout the cyclic loading is achieved by an integrated multi-scale progressive failure analysis extended FEM solution: (a) damage tracking predicts percentage contributing translaminar and interlaminar failure type, initiation, propagation, crack growth path, and observed shift in failure modes, and (b) fracture mechanics (VCCT, DCZM) predicts crack growth (Crack Tip Energy Release Rate vs. Crack Length), and delamination. The predictive methodology is verified using a building block validation strategy that uses: (a) composite material characterization and qualification (MCQ) software, and (b) the GENOA multi-scale progressive failure analysis fatigue life, stiffness degradation, and post-fatigue strength predictions for open-hole specimens under tension/compression at RTD. The unidirectional tension, compression, and in-plane shear lamina properties supplied by Lockheed Martin Aeronautics and the Air Force Research Laboratory (based on the D3039, D638, D3518 tests) were used by MCQ to reverse engineer effective fiber and matrix static and fatigue properties for the IM7-977-3 material system. The use of constituent properties identified the root cause problem for composite failure and enabled the detection of damage at the micro-scale of the material where damage is incepted. For all three case studies (namely, layups [0/45/90/−45]2s, [+60, 0, −60]3s, and [+30, +60, 90, −60, −30]2s), the blind predictions on the fatigue stiffness degradation and residual strength of the open-hole coupon in tension/compression under cyclic loading (with R = 0.1) at RTD were evaluated using a FE mesh (made of 2k shell elements), in which only one shell element, containing all plies, was employed through the thickness. The results of all analyses correlated very well with the tests, including the damage micro-graphs generated during the cyclic loading.

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de Morais, Alfredo Balacó. "Open-hole tensile strength of quasi-isotropic laminates". Composites Science and Technology 60, nr 10 (sierpień 2000): 1997–2004. http://dx.doi.org/10.1016/s0266-3538(00)00089-0.

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Kameo, Koji, Joop de Haan, Asami Nakai i Hiroyuki Hamada. "Open Hole Tensile Behaviors of Knitted Fabric Composites". Journal of Reinforced Plastics and Composites 18, nr 17 (listopad 1999): 1605–17. http://dx.doi.org/10.1177/073168449901801705.

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Achard, Victor, Christophe Bouvet, Bruno Castanié i Clément Chirol. "Discrete ply modelling of open hole tensile tests". Composite Structures 113 (lipiec 2014): 369–81. http://dx.doi.org/10.1016/j.compstruct.2014.03.031.

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Xu, Liang, Yi He, Yaoxiong Jia, Shaohua Ma i Li Hui. "Effects of thermal–oxidative aging on the mechanical properties of open-hole T800 carbon fiber/high-temperature epoxy composites". High Performance Polymers 32, nr 5 (31.10.2019): 494–505. http://dx.doi.org/10.1177/0954008319883691.

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T800 carbon fiber/high-temperature epoxy resin composites with holes were subjected to thermal–oxidative aging, and the effects of different aging temperatures and times on the composite properties were investigated. The mass loss, surface topography, open-hole tensile performance, fracture morphologies, dynamic mechanical properties, and infrared spectra were analyzed. The results showed that chemical aging did not occur with thermal–oxidative aging at 70°C and 130°C. However, chemical aging occurred at 190°C. At 70°C, 130°C, and 190°C, all samples showed a slight increase followed by a slight decrease and stabilization in the open-hole tensile strength. The open-hole tensile strength was maximized after 240 h aging at different temperatures; the open-hole tensile strength after 1920 h aging exceeded that of the unaged samples. All composites experienced through-hole failure. With aging, the glass transition temperature ( T g) was gradually increased and then decreased. After 960 h aging at different temperatures, T g was maximized.

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Zhu, Yingdan, Shijie Qi, Hongli Jia, Pengcheng Shi, Youqiang Yao, Junfeng Hu, Philippe Boisse i Haibing Xu. "Assessing tensile behavior of open-hole variable angle tow composites using a general gradient property simulation methodology". Journal of Reinforced Plastics and Composites 39, nr 19-20 (26.06.2020): 742–57. http://dx.doi.org/10.1177/0731684420929094.

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Variable Angle Tow placement is a way to steer individual curvilinear fibers. This work presents the assessment of tensile behavior of open-hole composite laminates with Variable Angle Tow reinforcement. A new multi-scale finite element method, consisting of a microscale unit cell model and a macroscale gradient property model, is developed to simulate Variable Angle Tow structures with various fiber trajectories. The tensile strength and the failure process of open-hole reinforced laminates with Variable Angle Tow reinforcement under tensile loading are predicted and analyzed. Experiments are also conducted to investigate reinforcing efficiency and failure modes of the open-hole laminates. The comparison of predicted and experimental results for the tensile strength and failure modes of T700/Epoxy laminates demonstrates clearly that the mechanical behavior of Variable Angle Tow structure can be simulated very well by the proposed multi-scale model. Moreover, it is found that the tensile strength of Variable Angle Tow laminates is closely related to the eccentricity and it reaches the maximum value only when the trajectories of curvilinear fibers keeps consistent with maximum principal stress trajectories of the open-hole plate.

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Kwame, J. S., E. Yakushina i P. Blackwell. "Examining Failure Behaviour of Commercially Pure Titanium During Tensile Deformation and Hole Expansion Test". Journal of Materials and Applications 9, nr 1 (15.05.2020): 32–37. http://dx.doi.org/10.32732/jma.2020.9.1.32.

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Hole expansion ratio is a material parameter which defines the extent to which sheet metals are formed. Research has shown that, the stress state observed at the hole edge after hole expansion test is similar to those observed during conventional uniaxial tensile test. However, conventional tensile test methods are not efficient in evaluating material edge formability. This work utilised optical non-contact measuring techniques to examine failure behaviour during tensile test and hole expansion test of commercially pure titanium sheet, fabricated with either abrasive water jet cutting or electric discharge machining. The work found that, the deformation mode in conventional tensile testing are governed by localised necking and subsequently diffused necking prior to failure. Deformation mode observed in hole expansion test is characterised by localised necking with no visible occurrence of diffused necking prior to failure. The highest strains are concentrated at the hole edge during hole expansion test due to their sensitivity to the hole preparation method with accompanying multiple localised necking sites resulting in non-uniform deformation. Strains become concentrated in the bulk material microstructure rather than the machined edge during tensile testing resulting in single localised deformation site and a more homogenous deformation.

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Krajangsawasdi, Narongkorn, Ian Hamerton, Benjamin K. S. Woods, Dmitry S. Ivanov i Marco L. Longana. "Open Hole Tension of 3D Printed Aligned Discontinuous Composites". Materials 15, nr 23 (6.12.2022): 8698. http://dx.doi.org/10.3390/ma15238698.

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This paper explores the use of Discontinuous Aligned Fibre Filament (DcAFF), a novel discontinuous fibre reinforced thermoplastic filament for 3D printing, to produce structural complex parts. Compared to conventional composite manufacturing, 3D printing has great potential in steering fibres around small structural features. In this current study, the initial thin carbon fibre (CF)-poly(L-lactic acid) (PLA) tape, produced with the High Performance Discontinuous Fibre (HiPerDiF) technology, is now reshaped into a circular cross-section filament, the DcAFF, using a bespoke machine designed to be scalable to high production rates rather than using a labour-intensive manual moulding method as in previous work. The filaments are then fed to a general-purpose 3D printer. Tensile and open-hole tensile tests were considered in this paper for mechanical and processability of DcAFF. The 3D printed specimens fabricated with the DcAFF show superior tensile properties compared to other PLA-based 3D printed composites, even those containing continuous fibres. Curvilinear open-hole tensile test samples were fabricated to explore the processability and performances of such material in complex shapes. The mechanical performance of the produced specimens was benchmarked against conventionally laid-up specimens with a cut hole. Although the steered specimens produced have lower strength than the fully consolidated samples, the raster generated by the printing path has turned the failure mechanism of the composite from brittle to ductile.

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Zhao, Quan Min, Jian Chun Fan, De Yan, Rui Rui Tian, Bo Zhou i Chun Li. "Development of Downhole Tools for Stratified Testing in Oil and Gas Open-Hole Wells". Advanced Materials Research 422 (grudzień 2011): 614–18. http://dx.doi.org/10.4028/www.scientific.net/amr.422.614.

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In view of the problems that multilayer stratified sampling and acidification-testing operations cannot be done in drill stem multilayer testing for open-hole wells, downhole tools for acidizing and testing were developed, stratified testing and sampling string, acidizing-testing string and their construction technology in open-hole wells were also studied. A set of technologies and equipment were provided for open-hole testing in exploratory wells. Field application shows the studying of drill stem stratified testing technology and related technological equipment can solve the problems existing in production, raise the working efficiency of open-hole testing, accelerate the speed of oil and gas exploration, and reduce the operating expenses.

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Xu, Liang, Guiting Wang, Song Zhou i Yanqing Huang. "Study on the effect of hygrothermal aging on the properties of three-dimensional woven composite materials with damage". Advances in Engineering Technology Research 6, nr 1 (6.07.2023): 365. http://dx.doi.org/10.56028/aetr.6.1.365.2023.

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This study analyzed the hygroscopic characteristics and mechanical properties of three-dimensional woven composite materials under 70℃/85%RH conditions and with the presence of damage. First, the materials underwent hygrothermal aging tests, including analysis of mass change, moisture absorption rate, SEM microstructure, Fourier-transform infrared spectroscopy (FT-IR), dynamic mechanical analysis (DMA), and subsequent open-hole tensile and compression strength tests under different environmental conditions. Finally, macroscopic failure analysis was conducted. The results showed that as the hygrothermal aging time increased, the moisture absorption rate increased and the fiber surface became smoother, while the degree of debonding between the fiber and matrix increased. The open-hole tensile and compression strength of the composite material decreased as the aging time extended, and the environmental temperature had different effects on open-hole tensile and compression strength.

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LIANG, SHUANGQIANG, QIHONG ZHOU i GE CHEN. "Open hole size effects on tensile properties of 3D braided composites". Industria Textila 72, nr 05 (30.10.2021): 545–51. http://dx.doi.org/10.35530/it.072.05.202010.

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Owing to the excellent integrated structure, notch-insensitivity, delamination-free characteristics, 3D braided composites have a broad range of engineering applications. In this paper, the notch size effects on two types of 3D braided composites were experimentally examined. Style I incorporated 40% of longitudinal lay-in yarns. Style II was the pure braids. The Point Stress Criterion (PSC) was applied to predict the open-hole strength of 3D braided composites. It is found the 3D braided composites can keep higher proportion residual strength after involving the different circular hole sizes compared to plain woven laminates. The open-hole pure braided specimen shows better performance than that the braids with longitudinal yarns, the lay-in longitudinal yarns improve neither specimens’ un-notched strength, nor the modulus. The predicted open-hole strength were compared with experimental results. The traditional analytical method can predict the open-hole strength of 3D braided composite to some extent. Under uniaxial tensile stress, the failure behaviour of two types of 3D braided specimens are different. For un-notched specimen, clear cracks usually show up on the Style II specimen, while it is not true for Style I coupon. For notched specimen, the crack of both notched specimens will propagate along the notch and finally render the specimen to fail

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Yunus, S., Z. Salleh, N. R. N. M. Masdek, Y. M. Taib, I. I. S. Azhar i K. M. Hyie. "Post-Impact and Open Hole Tensile Of Kenaf Hybrid Composites". IOP Conference Series: Materials Science and Engineering 328 (marzec 2018): 012017. http://dx.doi.org/10.1088/1757-899x/328/1/012017.

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Bao, Hongchen, i Guangyan Liu. "Progressive failure analysis on scaled open-hole tensile composite laminates". Composite Structures 150 (sierpień 2016): 173–80. http://dx.doi.org/10.1016/j.compstruct.2016.05.017.

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Kang, Huairong, Pengfei He, Cunman Zhang, Ying Dai, Zhongde Shan, Yong Zang i Hong Lv. "Tensile progressive damage and compressive postbuckling analysis of open-hole laminate composites". Journal of Reinforced Plastics and Composites 39, nr 17-18 (28.06.2020): 637–53. http://dx.doi.org/10.1177/0731684420920355.

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Laminate composites contain holes as a means of connection in industrial applications. A better understanding of the mechanical properties of open-hole components is necessary. Herein, progressive damage postbuckling analysis models are proposed for investigation of tensile damage and compressive buckling behaviors of open-hole laminate composites. The progressive damage model is based on failure criteria provided by the continuum damage mechanics model; virtual crack closure technology was employed to calculate the energy release rate for crack delamination in compressive postbuckling analysis. The models were utilized to analyze variations in the tensile and compressive mechanical properties, failure process, and buckling evolution of open-hole laminate composites using finite element analysis. The tensile failure patterns and failure processes of plies with different open-hole laminate composite angles were obtained and analyzed. Buckling characteristics, as well as the progression of buckling onset, buckling propagation, crack delamination, unstable delamination, and global buckling, were investigated. The influence of delamination crack length and crack distribution on the buckling properties of open-hole laminate composites are discussed in detail. Additionally, unstable and stable buckling characteristics were examined. The numerical results were in good agreement with theoretical and experimental results; damage initiated at the edge of a hole propagated to two sides with the onset of matrix damage, followed by fiber damage. The fiber damage of a 0°-ply led ultimately to laminate failure. The laminate with a symmetrical crack distribution showed stable buckling, whereas a short, nonsymmetrical distribution of cracks usually led to unstable buckling and delamination.

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Ghasemi, Ahmad Reza, Ali Tabatabaeian i Mehdi Moradi. "A new insight into impact of thermal cycling on the un-notched and circular hole polymeric composite rings via naval ordnance laboratory-ring test". Journal of Composite Materials 54, nr 23 (24.03.2020): 3287–95. http://dx.doi.org/10.1177/0021998320912836.

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In this paper, different mechanical responses of polymer matrix composite rings under thermal cycling are analyzed. The polymer matrix composite rings are classified to un-notched and open-hole specimens and tested based on the naval ordnance laboratory-ring tensile test method. Internal pressure, fracture and surface degradation changes as a function of the hole diameter and number of cycles are investigated. Experimental results suggest that specimens with larger hole radius have more mechanical property variations during thermal cycling. Also, it is revealed that the mechanical properties of laminates degrade as a function of the number of cycles and the hole diameter. The results also demonstrate that long splitting fiber breakage is the main mode for the failure of un-notched specimens, whereas fiber breakage and fiber matrix debonding are the two main modes for the failure of open-hole specimens. Finally, a multiple regression model is proposed to predict the tensile response of un-notched and open-hole polymer matrix composite rings subjected to thermal cycling condition.

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Hisker, Frank, Richard Thiessen i Thomas Heller. "Influence of Microstructure on Damage in Advanced High Strength Steels". Materials Science Forum 706-709 (styczeń 2012): 925–30. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.925.

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AHSS (Advanced High Strength Steels) combine high strength and good ductility. Their outstanding forming and work-hardening behavior predestines these steels for fabrication of strength relevant structural elements and automobile body parts. To characterize a material, not only tensile, but also hole-expansion and bending behavior are important and help predict the stretch-flange-formability. In this study, detailed analyses of the correlation between these three tests and the damage mechanisms during forming have been performed for selected steels. The results show that for AHSS one should differentiate between “local” and “global” failure. Furthermore, not only are certain materials more sensitive to local or global damage, but also various testing methods tend to provoke either local or global damage. Tensile testing provokes global failure whereas hole-expansion tends to induce local failure. A specimen fails during bending with a mixture of local and global modes. These failure modes are strongly attributed to the microstructure. DP-steels yield high elongation during tensile testing and poorer hole-expansion values. High-resolution EBSD has revealed that the microstructure of DP-steels is sensitive to localized damage, which is compensated by work-hardening around damaged regions and thus shifts the loading to un-hardened regions. This makes DP-microstructures well-suited to tensile loading but sensitive to hole-expansion. CP-steels of comparable strength show poorer tensile elongation and higher hole-expansion ratios due to a microstructure which is not sensitive to localized failure (but has limited capacity for work-hardening). The failure mode in TRIP-steels exhibits a similar character as in DP-steels, but only after the martensitic transformation of retained austenite.

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Zhou, Song, Yi Sun, Boyang Chen i Tong-Earn Tay. "Material orthotropy effects on progressive damage analysis of open-hole composite laminates under tension". Journal of Reinforced Plastics and Composites 36, nr 20 (30.05.2017): 1473–86. http://dx.doi.org/10.1177/0731684417710329.

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The sizes effects on the strengths of open-hole fibre-reinforced composite laminates subjected to tensile loading (OHT) have been investigated widely. However, little attention has been paid to the influence of material orthotropy. This paper presents a progressive damage model for the model failure of notched laminates under tensile loading based on continuum damage mechanics and cohesive elements. The effects of orthotropy on the failure of notched laminates with seven different ply sequences are investigated by our proposed model. The prediction results adopting the Hoffman and Pinho failure criterions to determine matrix damage initiation are compared with the results of experiments. Our proposed models are able to predict the strong influence of orthotropy on strengths of open-hole laminate under tension, and model using Pinho criterion can predict the open-hole tension strength most accurately.

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Plosila, P., V. Kesti, A. Kaijalainen, R. Vierelä, P. Rautio i J. Kömi. "Strain evolution during hole expansion testing of 800 MPa tensile strength hot-rolled steels". IOP Conference Series: Materials Science and Engineering 1284, nr 1 (1.06.2023): 012022. http://dx.doi.org/10.1088/1757-899x/1284/1/012022.

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Abstract One limitation of the standardized ISO 16630 hole expansion test is that it provides only one result: limiting hole expansion ratio (HER). In practice, steels with similar HER values can have different cut edge forming behavior due to possible differences in strain localization tendencies. Digital image correlation (DIC) strain measurement during formability testing allows more in-detail analysis of strain-state near the cut edge. In this paper, strain evolution during hole expansion testing was investigated for three 800 MPa tensile strength grade hot-rolled strip steels. The steels were selected to have differences in microstructures and anisotropies of mechanical properties. Two different hole expansion test methods with DIC strain measurement were utilized to investigate different edge loading scenarios: in-plane stretching with a flat-top punch and more out-of-plane stretching with a hemispherical punch. Test holes were prepared according to ISO 16630 standard. In order to examine strain evolution and localization during testing, strains were measured with circle-shape sections around the hole in various distances from the cut edge. Strain localization behavior was investigated in different sheet directions and the effect on the hole expansion ratio was evaluated. Results show considerable differences in the cut edge forming behavior between the investigated materials.

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Chen, B. Y., T. E. Tay, P. M. Baiz i S. T. Pinho. "Numerical analysis of size effects on open-hole tensile composite laminates". Composites Part A: Applied Science and Manufacturing 47 (kwiecień 2013): 52–62. http://dx.doi.org/10.1016/j.compositesa.2012.12.001.

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Yu, Jiajia, Zhongxiang Pan, Qimao Cai, Fa Zhang i Zhenyu Wu. "Open hole tensile behavior of plain woven carbon/glass hybrid composites". International Journal of Mechanical Sciences 246 (maj 2023): 108142. http://dx.doi.org/10.1016/j.ijmecsci.2023.108142.

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Bale, Jefri, Kristomus Boimau i Marselinus Nenobesi. "Natural Composite Reinforced by Lontar (Borassus flabellifer) Fiber: An Experimental Study on Open-Hole Tensile Strength". International Journal of Biomaterials 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/7685047.

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A research has been conducted in the present study to investigate the effect of hole configuration on tensile strength of lontar fiber-reinforced composites. The lontar fiber-reinforced composites used in this study were produced by hand lay-up process. The lontar fiber-reinforced composites consist of short random fiber of 5 cm that contains 32% of nominal fiber volume as the reinforcement and unsaturated polyester as the matrix. The results show that the differences of hole configuration have an effect on tensile strength of lontar fiber-reinforced composites. It is found that the specific area of four-hole specimens experiences smaller strain propagation due to the redistributed stress and no stress passes through the hole. The damage of lontar fiber-reinforced composites with different hole configurations in tension is fairly straight and transverse to the loading axis, where the initial damage occurs in the form of matrix cracking, propagates into interfacial failure in form of delamination, and ultimately failed mainly due to the fiber breakage.

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44

Sirmour, S., U. Kumar, H. Chandrakar i N. Gupta. "Open Hole Testing Methods for Different Materials: A Review". IOP Conference Series: Materials Science and Engineering 561 (12.11.2019): 012037. http://dx.doi.org/10.1088/1757-899x/561/1/012037.

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Kalyanasundaram, Dinesh, Suhasini Gururaja, Prajakta Prabhune i Dilpreet Singh. "Open hole fatigue testing of laser machined MD-CFRPs". Composites Part A: Applied Science and Manufacturing 111 (sierpień 2018): 33–41. http://dx.doi.org/10.1016/j.compositesa.2018.05.005.

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Cao, Zi Zhen, Ji Feng Zhang, Yun Wan i Yong Gang Xie. "A Damage Model for Prediction of the Open-Hole Strength of Glare Laminates". Applied Mechanics and Materials 325-326 (czerwiec 2013): 123–27. http://dx.doi.org/10.4028/www.scientific.net/amm.325-326.123.

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A three-dimensional progressive damage model is proposed to predict the open-hole tensile strength of Glare laminates. For the glass fiber reinforced epoxy the user subroutine UMAT is employed for description of the failure modes, such as matrix cracking and fiber failure. Behavior of the delamination between plies of the laminate is described using cohesive elements. Laminates with a rhombic hole, a square hole and a circular hole are taken into consideration separately. The results obtained by the present solution approach are validated with those available in the literatures.

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47

Wang, Xiao Qiang, Wei Tao Zhao, Bo Fang, Shao Wei Lu i Ye Wei Zhang. "Finite Element Analysis of the Tensile Properties of Composite Laminates with Open Holes". Advanced Materials Research 1004-1005 (sierpień 2014): 451–54. http://dx.doi.org/10.4028/www.scientific.net/amr.1004-1005.451.

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For different technical reasons, cutouts such as holes in thin-walled structures are inevitable and are of significant technical relevance. Unfortunately open holes usually lead to an undesired stress concentration at the hole vicinity and a reduced load carrying ability of the structure. Therefore the mechanical properties of fiber-reinforced composite laminates with open holes are studied in the paper. The influences of the size and shape of the holes are investigated. A progressive failure finite element model is developed with software ABAQUS. Different failure modes of the composite laminates with various holes are simulated under the Hashin failure criterion. The computational results show that the hole/s have a significant effects on composite laminates properties, and the conclusion can be provided as a good reference for the design of the composite laminates with hole/s.

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Wang, Hongxiao, Xiaohui Zhang i Yugang Duan. "Investigating the Effect of Low-Temperature Drilling Process on the Mechanical Behavior of CFRP". Polymers 14, nr 5 (4.03.2022): 1034. http://dx.doi.org/10.3390/polym14051034.

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Previous research has found that lower temperature drilling is helpful to improve the hole quality of carbon fiber reinforced polymer (CFRP). However, the influence of the lower temperature drilling process on the mechanical behavior of composites is yet not fully understood. To examine the influence of the lower temperature drilling process on the mechanical behavior of CFRP, the open hole CFRP specimens used for mechanical tests were obtained with three cases: drilling with −25 °C/uncoated carbide drills/(1000 rpm, 0.02 mm/r), 23 °C/coated carbide drills/(4000 rpm, 0.03 mm/r), and 23 °C/uncoated carbide drills/(1000 rpm, 0.02 mm/r), respectively; corresponding, three groups of open-hole specimens are obtained: specimens drilling at low-temperature with low damage, specimens drilling at room-temperature with low damage and specimens drilling at room-temperature with low damage; the mechanical behavior of the three groups specimens were obtained by static tensile, tensile–tensile fatigue cyclic tests and residual tensile strength test. The results have shown that the mechanical properties of specimens with a low-temperature drilling process is lower than those of the specimen with a normal drilling process due to the better drilling quality. The damage accumulation in specimens was increased with the damage degree of the original hole, the greater the damage degree, the worse the mechanical properties.

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Goltsev, V. Yu, A. V. Osintsev, A. S. Plotnikov i V. I. Polskij. "Diametral compression of short cylinders with a central hole as a method for assessing the tear resistance of brittle materials". Industrial laboratory. Diagnostics of materials 89, nr 7 (26.07.2023): 45–50. http://dx.doi.org/10.26896/1028-6861-2023-89-7-45-50.

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The possibility of evaluating the tear resistance of brittle materials by diametral compression test of short cylinders (solid and central with a central hole) has been analyzed. The computational analysis was performed by the finite element method using the ANSYS program. It is shown that the stress distribution in a disk with a hole is similar that without a hole but contains disturbances introduced by a stress concentrator in the form of a hole. The normalized values of the maximum first principal stresses for a disk with a hole exceed the values for a disk without a hole by more than 5 times. The experimental analysis was carried out by testing short cylinders, both solid and with a central hole, made of brittle materials: cast iron and graphite. It is noted that the fracture resistance, determined by the formula recommended by the ASTM D3967 – 95a standard, practically does not differ for solid cast iron samples, and for graphite differs by 1.5 times from the true tear resistance of materials; when testing samples with a central hole, the tear resistance differs from the standard values by a factor of 1.5 and almost 2.5, respectively. The different nature of the sample destruction is also noted: slow controlled rupture of cast iron and dynamic destruction of graphite with the corresponding deformation diagrams. The results of testing fuel pellets of uranium dioxide are given as an example of testing real cylindrical samples with a central hole. It is shown that the test results of ARV-1 graphite samples are in good agreement with the test results of fuel samples. Thus, the possibility of testing small-sized short cylinders according to the diametral compression scheme for indirect assessment of the tensile strength of brittle materials has been confirmed. A calculation formula is proposed for an indirect assessment of the tensile strength of brittle materials based on the results of testing small-sized short cylinders, both with and without a central hole according to the diametral compression scheme.

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Yuwei, Li, Ai Chi, Liu Yu i Gao Changlong. "The Breakdown Pressure Calculating Model for Open Hole Completion CBM Well Hydraulic Fracturing". Open Fuels & Energy Science Journal 7, nr 1 (7.03.2014): 12–19. http://dx.doi.org/10.2174/1876973x01407010012.

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The open hole completion CBM borehole wall intersects with the weak surface such as cleats and fractures. In the process of hydraulic fracturing, the fractures may origin from coal body or cleats, which makes the rupture mechanism and rupture models of the borehole wall being different from the conventional reservoirs. The previous model for calculating breakdown pressure of open hole completion borehole wall considering tension failure has poor applicability for calculating breakdown pressure. Considering the spatial relationship of the intersection of borehole wall and cleats, analyzing the stress state of borehole wall rock and cleats wall, and basing on elastic mechanics and fracture mechanics, the breakdown pressure calculation model for CBM open hole completion hydraulic fracturing was established. In the model, fractures initiate from coal rock body, tensile failure along with face cleats, shear failure along with face cleats, tensile failure along with butt cleats and shear failure along with butt cleats five kinds of damage modes were considered. According to example calculation, the breakdown pressure of HX-L1 well calculated using the model is 14.81 MPa. The actual pressure obtained by bottom hole pressure gage is 15.42 MPa, and the relative error is 3.96%. The calculated result agrees with the actual conditions. It can be concluded that the model can be used to calculate the breakdown pressure for open hole completion CBM well hydraulic fracture.

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