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1. Screw connections to full-culm bamboo

   Morrill, P.; Rogers, C.; Flower, C.; Akinbade, Y.; Harries, K.A. (January 2019, 18th International Conference on Non-Conventional Materials and Technologies (18NOCMAT))

   The use of screw connections in full-culm bamboo is often assumed to be limited, primarily due to the propensity for splitting of the culm. This study demonstrates that small diameter screws can be used effectively in full-culm bamboo. The study explores the withdrawal capacity of candidate screw types in order to identify those that may be used to achieve a high capacity while mitigating splitting failures. Twelve screw types of three standard sizes, ranging from hardwood screws, self-tapping wood screws and concrete anchors, are tested in conditions of both pre-drilled and self-tapping installation procedures. All tests are conducted on samples of P. edulis (Moso) having culm wall thickness on the order of 7 mm. The results of this study are intended to inform the applications for which screw connection to bamboo are viable. 

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2. Screw connections to full-culm bamboo

   Morrill, P.; Rogers, C.; Flower, C.; Akinbade, Y.; Harries, K.A.. (January 2019, 18th International Conference on Non-Conventional Materials and Technologies (18NOCMAT))

   The use of screw connections in full-culm bamboo is often assumed to be limited, primarily due to the propensity for splitting of the culm. This study demonstrates that small diameter screws can be used effectively in full-culm bamboo. The study explores the withdrawal capacity of candidate screw types in order to identify those that may be used to achieve a high capacity while mitigating splitting failures. Twelve screw types of three standard sizes, ranging from hardwood screws, self-tapping wood screws and concrete anchors, are tested in conditions of both pre-drilled and self-tapping installation procedures. All tests are conducted on samples of P. edulis (Moso) having culm wall thickness on the order of 7 mm. The results of this study are intended to inform the applications for which screw connection to bamboo are viable. 

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

   Tushar, Telmasre; Abdelrahman, Abdelmotagaly; Gao, Yanfei; Yu, Zhenzhen (January 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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5. Post-Buckling Mechanics of a Square Slender Steel Plate in Pure Shear

   Garlock, M; Quiel, S; Wang, P; Alos-Moya, J; Glassman, J. (January 2019, Engineering journal)

   Thin (slender) steel plates possess shear strength beyond the elastic buckling load which is commonly referred to as the post-buckling capacity. Semi-empirical equations based on experimental tests of plate girders have been used for decades to predict the ultimate post-buckling strength of slender webs. However, several recent studies have shown that the current models for predicting the ultimate shear post-buckling capacity of thin plates are based on some incorrect assumptions regarding their mechanical behavior. As a result, the current design equations provide an approximate estimate of capacity for the range of parameters in the test data upon which they are founded. This paper explores the fundamental behavior of thin plates under pure shear. Such a fundamental examination of shear post-buckling behavior in thin plates is needed to enable design procedures that can optimize a plate’s shear strength and load-deformation performance for a wider range of loading and design parameters. Using finite element analyses, which are validated against available results of previous experimental tests, outputs such as plastic strains, von Mises stresses, principal stresses, and principal stress directions are examined on a buckled plate acting in pure shear. The internal bending, shear, and membrane stresses in the plate’s finite elements are also evaluated. In this study, these evaluations are performed for a simply-supported plate with an aspect ratio equal to 1.0 and slenderness ratio equal to 134. Results show that localized bending in the plates due to the out-of-plane post-buckling deformations appear to be a significant factor in the ultimate shear post-buckling capacity of the plate. Also, the compressive stresses continue to increase beyond the onset of elastic buckling in some regions of the plate, contrary to current design assumptions. Overall, this study provides new insights into the mechanics of shear post-buckling behavior of thin plates that can be exploited for design procedures that are consistent with mechanical behavior. 

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