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1. Geometric effects on competing failure modes in lap shear testing of spot joints

   Telmasre, T.; Abdelmotagaly, A.; Gao, Y.; Yu, Z. (September 2022, China Welding)

   When subjected to the lap shear testing, spot welds created by brazing, resistance welding, or other techniques may fail either by a plug failure mode (also called pull-out mode) or an interfacial shear failure mode. In the past, plug failure mode was thought to be depend- ent on base metal ultimate tensile strength, spot diameter and plate thickness, while interfacial failure can be determined by interface shear strength and spot area. No fracture mechanics model or failure process is invoked in such an approach, and its predictive capability is often doubted compared to realistic experiments. This work conducts a parametric study to assess the failure behavior as a function of dominant three-dimensional geometric parameters based on the Gurson-Tvergaard-Needleman (GTN) damage mechanics model and no-damage mod- el respectively. Different necking conditions are considered as precursors to the two failure modes in the no-damage model. It is found out that a small ratio of spot diameter to plate thickness promotes interfacial shear failure while a large ratio favors plug failure. Other geometric parameters such as the filler interlayer thickness, if used, play a secondary role. The calculated peak force Fwt is not much different between the GTN and no-damage analyses, and better agreement is shown in the small nugget region. Normalized peak force calculated from the GTN model with the porosity f0 set to 0.01 showed the best agreement with pervious tensile shear tests on spot-welded DP980 lap joints in comparison to that calculated from the GTN model with f0 at 0.02 and the no-damage model. Note that heterogeneous distribution of materi- al strength across the joint region was considered in the GTN model, which was estimated based on the hardness map measured across the joint cross section. 

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2. Comparative Analysis of Different Adhesive Model Representations in Single Lap Joints Using Finite Element Analysis

   https://doi.org/10.3390/app15052661  

   Adediran, Ibrahim; Fritz, John; Truster, Timothy (March 2025, Applied Sciences)

   This study addresses an existing gap in the literature by providing a comparative analysis of various adhesive model representation approaches, using cohesive zone models—both local and continuum models. Through a systematic investigation of stress distribution and force–displacement characteristics across different modeling techniques, we reveal the advantages and limitations of each method. This study provides a comparison of various adhesive modeling approaches, including single-row cohesive elements, interfacial elements, middle cohesive elements, and single-row continuum solid elements, highlighting their effects on stress distribution and failure modes in single lap joints across a range of adherend thicknesses and overlap lengths. The findings demonstrate that the choice of modeling techniques yields a similar prediction of failure modes in single lap joints under tensile loading. Consequently, choosing among these methods can be guided by the level of detail in capturing localized damage mechanisms. The results offer a foundation for informed decision making in adhesive modeling, with implications for improving joint design and reliability in real-world applications. 

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3. Polyacrylamide hydrogels. III. Lap shear and peel

   https://doi.org/10.1016/j.jmps.2021.104348  

   Wang, Yecheng; Yin, Tenghao; Suo, Zhigang (May 2021, Journal of the Mechanics and Physics of Solids)

   Lap shear and peel are common tests for soft materials. Their results, however, are rarely compared. Here we compare lap shear and peel as tests for measuring toughness. We prepare specimens for both tests by using stiff layers to sandwich a layer of a polyacrylamide hydrogel. We introduce a cut in the hydrogel by scissors, pull one stiff layer at constant velocity, and record the force. In lap shear, the force peaks and then drops to zero, the cut grows unstably through the entire hydrogel, and the peak force is used to determine toughness. In peel, the force peaks and then drops to a plateau, the cut grows in the hydrogel in steady state, and the plateau force is used to determine toughness. Our experimental data show that the average values of toughness determined by lap shear and peel are comparable. The peak forces in both tests scatter significantly, but the plateau force in peel scatters narrowly. Consequently, toughness determined by lap shear scatters more than toughness determined by peel. We hypothesize that the peak forces scatter mainly due to the statistical variation of the cuts made by scissors, and test the hypothesis using two additional sets of experiments. First, after a cut is made by scissors, we pre-peel the specimen to extend the cut somewhat, and then measure toughness by lap shear and peel. The peak force in lap shear scatters less, and the peak force in peel is removed. Second, we prepare cuts using spacers of various thicknesses, and find that the peak forces in both lap shear and peel vary with the thickness of the spacer. These findings clarify the use of lap shear and peel to characterize soft materials. 

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4. Evaluation of the Effect of Thermal Oxidation and Moisture on the Interfacial Shear Strength of Unidirectional IM7/BMI Composite by Fiber Push-in Nanoindentation

   https://doi.org/10.1007/s11340-017-0335-6  

   Xu, T.; Luo, H.; Xu, Z.; Hu, Z.; Minary-Jolandan, M.; Roy, S.; Lu, H. (August 2017, Experimental Mechanics)

   Fiber push-in nanoindentation is conducted on a unidirectional carbon fiber reinforced bismaleimide resin composite (IM7/BMI) after thermal oxidation to determine the interfacial shear strength. A unidirectional IM7/BMI laminated plate is isothermally oxidized under various conditions: in air for 2 months at 195 °C and 245 °C, and immersed in water for 2 years at room temperature to reach a moisturesaturated state. The water-immersed specimens are subsequently placed in a preheated environment at 260 °C to receive sudden heating, or are gradually heated at a rate of approximately 6 °C/min. A flat punch tip of 3 μm in diameter is used to push the fiber into the matrix while the resulting loaddisplacement data is recorded. From the load-displacement data, the interfacial shear strength is determined using a shear-lag model, which is verified by finite element method simulations. It is found that thermal oxidation at 245 °C in air leads to a significant reduction in interfacial shear strength of the IM7/BMI unidirectional composite, while thermal oxidation at 195 °C and moisture concentration have a negligible effect on the interfacial shear strength. For moisture-saturated specimens under a slow heating rate, there is no detectable reduction in the interfacial shear strength. In contrast, the moisture-saturated specimens under sudden heating show a significant reduction in interfacial shear strength. Scanning electron micrographs of IM7/BMI composite reveal that both thermal oxidation at 245 °C in air and sudden heating induced microcracks and debonding along the fiber/matrix interface, thereby weakening the interface, which is the origin of failure mechanism. 

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5. Determining ideal strength and failure mechanism of thermoelectric CuInTe ₂ through quantum mechanics

   https://doi.org/10.1039/C8TA03837F  

   Li, Guodong; An, Qi; Morozov, Sergey I.; Duan, Bo; Zhai, Pengcheng; Zhang, Qingjie; Goddard III, William A.; Snyder, G. Jeffrey (January 2018, Journal of Materials Chemistry A)

   CuInTe 2 is recognized as a promising thermoelectric material in the moderate temperature range, but its mechanical properties important for engineering applications remain unexplored so far. Herein, we applied quantum mechanics (QM) to investigate such intrinsic mechanical properties such as ideal strength and failure mechanism along with pure shear, uniaxial tension, and biaxial shear deformations. We found that the ideal shear strength of CuInTe 2 is 2.43 GPa along the (221)[11−1] slip system, which is much lower than its ideal tensile strength of 4.88 GPa along [1−10] in tension, suggesting that slipping along (221)[11−1] is the most likely activated failure mode under pressure. Shear induced failure of CuInTe 2 arises from softening and breakage of the covalent In–Te bond. However, tensile failure arises from breakage of the Cu–Te bond. Under biaxial shear load, compression leads to shrinking of the In–Te bond and consequent buckling of the In–Te hexagonal framework. We also found that the ideal strength of CuInTe 2 is relatively low among important thermoelectric materials, indicating that it is necessary to enhance the mechanical properties for commercial applications of CuInTe 2 . 

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