The tension test parallel-to-fiber in anisotropic materials, such as bamboo, is one of the most important tests because it makes it possible to evaluate mechanical properties used in calculations for ...different types of stresses. For this type of test there are standards that apply to wood in general, others to bamboo, and other more specific ones that apply to bamboo Guadua angustifolia Kunth. These rules suggest the use of dog bone test specimens. When performing such tests parallel to the fiber direction, failures are observed in undesired zones. This document characterizes and analyzes the possible types of failures. It also evidences the difficulties presented and quantifies them finding that, for 59 failed test pieces, only 18.6% had failures within the desired zones, while the other 81.4% had failures within undesired zones in the tension test parallel to the fiber. Finally, it can be concluded that there are gaps in the rules that influence the variation of the results obtained by different authors. The dog bone test specimens are not recommended for tension tests parallel to the Guadua fiber. Rather, utilization of straight specimens is recommended with a calculated clamping height and the standard equation and protected clamping area.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•A novel analytical strength estimator for the SPR joint is developed.•The strength estimator is based on local mechanical responses of rivet and sheets through observation in FE simulation.•FE ...simulations are validated with different fracture models and deformed states between riveting and strength models.•The four parameter joint strength estimator gives excellent agreement with lap-shear and cross-tension experiments.
Analytical strength estimators for self-piercing riveted (SPR) metal sheets under the lap-shear and the cross-tension modes are developed. The modeling is based on the local mechanical responses of rivet and sheet metals during the riveting process and joint strength tests, which are investigated using finite element (FE) simulations as virtual experiments. The FE simulations consist of the riveting process model and lap shear test model, and the plastic strain hardening and damage of sheet metals near the riveted zone are transferred between the two models. The cross-sectional geometry of the riveted zone and the load-displacement curve during the lap-shear test are predicted with three different ductile fracture criteria, Cockcroft–Latham, Rice–Tracey, and Drucker–Prager model, to evaluate the accuracy of the FE modeling. The four-parameter joint strength estimator for the lap-shear and cross-tension are proposed based on the observations of the geometrical features and mechanical responses in the FE simulations. The results of prediction are within reasonable accuracy for various combinations of steel and aluminum alloy sheets, particularly 31 among 34 cases showed prediction errors within 25% for the lap shear-tests, and 14 among 18 cases for the cross-tension tests, and average errors for lap-shear and cross-tension mode were 12.1% and 14.4%, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Hydrogen embrittlement of a precipitation-hardened Fe–26Mn–11Al-1.2C (wt.%) austenitic steel was examined by tensile testing under hydrogen charging and thermal desorption analysis. While the high ...strength of the alloy (>1 GPa) was not affected, hydrogen charging reduced the engineering tensile elongation from 44 to only 5%. Hydrogen-assisted cracking mechanisms were studied via the joint use of electron backscatter diffraction analysis and orientation-optimized electron channeling contrast imaging. The observed embrittlement was mainly due to two mechanisms, namely, grain boundary triple junction cracking and slip-localization-induced intergranular cracking along micro-voids formed on grain boundaries. Grain boundary triple junction cracking occurs preferentially, while the microscopically ductile slip-localization-induced intergranular cracking assists crack growth during plastic deformation resulting in macroscopic brittle fracture appearance.
•Hydrogen embrittlement was observed in an austenitic steel with κ-carbide.•The hydrogen embrittlement was caused by grain boundary cracking.•An important crack initiation site is grain boundary triple junction.•Strain localization was observed particularly along grain boundaries.•The strain localization promotes the hydrogen embrittlement.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Crack failure analysis has been done on exhaust manifold of a diesel engine.•Crack propagation at maximum work temperature has been discussed.•Crack failure toughness has been determined during ...finite element analysis.•Critical fracture force of D5S has been determined at 800 ˚Cby tension test.Critical fracture toughness has been determined by using of finite element analysis.Critical crack length has been calculated.It was concluded that assumed crack does not propagates during worst work condition.
D5S is an alloy used in the manufacture of exhaust manifold of the internal combustion (IC) engines. Considering that exhaust manifold is one of the engine components that are under intense thermal and mechanical loads, fracture failure analysis should be regarded for this engine part. Fracture toughness determination is the main criterion for structural fracture analysis. In this research, crack failure was analyzed based on the finite element method (FEM), upon which critical fracture toughness was determined. Using the FEM analysis, a crack was assigned on the exhaust manifold model in order to obtain its fracture toughness at the first mode (KI) under thermo-mechanical loads. According to the ASTM standard, four compact tension (CT) specimens with different notch lengths of 4 mm, 5 mm, 9 mm, and 12 mm were prepared. Then, using the tension test at a high temperature, critical fracture force was determined. CT specimens were simulated by the finite element ABAQUS software. Fracture force obtained from the tension test was exerted on the CT specimen in the simulation software. Then, critical fracture toughness (KIC) was gained by using the fracture analysis in FE simulation. Finally, KI was compared with KIC and crack propagation was discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study proposes an inverse methodology for determining the strain hardening behaviors at large deformation of titanium alloys using uniaxial tensile and notched tests with finite element ...analysis. Various hardening laws and data fitting range are considered to characterize the stress-strain relationships of commercially pure titanium (CP-Ti) and Ti6Al4V alloys which can increase the flexibility of identifying the proper models. A new hybrid HHSL hardening model is presented for CP-Ti and its parameters are obtained by iteratively minimizing the difference between the finite element simulation and experimental data. The hardening behavior of Ti6Al4V alloy is predicted by the weighted HSV model. The results show that mechanical response and loading curves from the identified numerical models are consistent with the experimental results of titanium alloys, demonstrating the validity and effectiveness of the proposed inverse approach in practical use.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The indirect tension test is an important laboratory test for rock characterization. The presence of rock fabric, such as schistosity, complicates the assessment of test results. One hundred and ...forty-five indirect tension tests were conducted on mica schist specimens to investigate the effect of schistosity orientation on failure mode and tensile strength. Tensile strength results did not provide a clear relationship between schistosity orientation and tensile strength, so the failure patterns were investigated. A new naming scheme for failure modes was developed, incorporating fracture patterns observed in the specimen faces and edges. The Single Mode failure group specimens had only one failure pattern that appeared on both specimen faces, either axial failure (seventy-three specimens), schistosity failure (six specimens), or out-of-plane failure (seven specimens). The Mixed Mode failure group had thirty-two specimens that exhibited one failure pattern on one face and another on the other. The Hybrid Mode failure group had twenty-seven specimens with multiple failure patterns on both specimen faces. It was noted that Mixed Mode and Hybrid Mode specimens with components of axial failure had higher indirect tensile strengths than specimens without elements of axial failures. Statistical analyses of the tensile strength data using Levene’s Test for equal variances and two-sample t-tests showed no statistical difference between the Mixed Mode and Hybrid Mode failure groups. However, there was a statistical difference between the tensile strengths of the Single Mode axial failure specimens and the combined Mixed Mode and Hybrid Mode failure groups. These results clearly emphasize that indirect tensile strength should be assessed using schistosity orientation and failure mode.
•Stainless steel (SS) 316L exhibits different stress–strain curves from ambient ones.•Decreasing T from 20 to −80℃ linearly increases the yield strength of SS 316L.•Decreasing T increases the ...ultimate strength, but reduces the ductility of SS 316L.•Proposed analytical models predict well low-temperature stress–strain curves of SS 316L.
To investigate mechanical behaviours of structural stainless steel (SS) 316L at cold-region cooling environment, this paper firstly performed tension tests on SS 316L at varying low temperatures. Thirty-two standard samples in different thickness, cut from different square/circular SS tubes, were tested under combined uniaxial tension and varying low temperatures (T) of −80, −60, −30, and 20 °C. These tests showed that the low-temperature stress–strain (σ-ε) curves behave differently from those ambient-temperature ones, which exhibits “S”-shaped strain hardening stages with a much larger sloped second strain hardening stage than that of the first strain hardening stage. Decreasing T from 20 to −80 °C increased the elastic modulus (E), yield (σ0.2) and ultimate (σu) strength of SS 316L, but reduced its ultimate (εu) and fracture (εF) strains as well as the ductility. However, all the SS 316L samples failed in ductile mode even though their ductility was compromised. Empirical models were also developed to estimate the enhancing factors for E, σ0.2, σu, and εu due to low temperatures using the best subset regression analysis method. In addition, modified true σ-ε constitutive models at low temperatures were also developed for SS 316L. The validations proved that the developed constative models described well the σ-ε behaviour of SS 316L at a low temperature range of −80 ∼ 20 °C.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study investigates the effects of ground tire rubber (GTR) on the cracking resistance of asphalt mortar from different analysis scales. Furthermore, the effectiveness of different fracture test ...methods was compared for GTR-modified asphalt mortar, including the indirect tensile cracking test (IDEAL-CT), disk-shaped compact tension test (DCT) and Illinois flexibility index test (I-FIT). To achieve this, a mesoscopic fracture test based on the SEM-Servo Plus device was proposed firstly to obtain the micro-parameters of constitutive models in discrete-element modelling (DEM). A unified fracture modelling procedure that can avoid any interference factors was carried out for comparative fracture analysis. Results from the tests and simulations show that rubber filler plays a positive role in enhancing the fracture properties of the asphalt mortar. The fracture energy measured by IDEAL-CT is almost 5-6 times of the DC(T) test and 1.5-2 times of the I-FIT test. It is not an inherent attribute of material and can only be regarded as a relative index for fracture resistance evaluation. The FI and CT
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obtained from the I-FIT and IDEAL-CT test show a weak correlation of fracture resistance, especially when comparatively evaluating the GTR-modified asphalt mortar with minor difference in filler content.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Tensile and compressive tests are carried out on four nanoporous gold samples with ligament sizes of 56, 149, 402, and 868 nm, all without grain boundaries and with similar number of ligaments ...regardless of ligament size. We find that tensile yield strengths are greater than compressive yield strengths up to ligament size of 402 nm, while yield strengths are similar in tension and compression for dL of 868 nm. The dependence of tensile yield strength on ligament size is described well using a size-effect exponent -1.18 for four samples, whereas bulk-like behavior, i.e. no ligament-size dependency, is observed for ligament size greater than 402 nm in compression; compressive yield strength depending on ligament size is described by a size-effect exponent -1.49 for ligament sizes ranging from 56 nm to 402 nm. The asymmetries in yield strength and plasticity between tension and compression are discussed in terms of the deformation behavior of individual ligaments based on a suggested open-cell model and dislocation activities in the ligaments.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
