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141.
142.
Delamination initiation and propagation in plain woven laminates and 3D orthogonal woven composites during short beam shear (SBS) test were analyzed using finite element (FE) analyses. Two kinds of 3D woven composites, containing single z-yarns and double z-yarns, were considered. The FE models were guided by experimental observations from SBS tests for the same material systems. A series of mechanisms including creation and evolution of matrix cracks and delaminations were modeled discretely. The force-displacement curves obtained from the FE simulations were compared with those from experiments. Further parametric studies were conducted to investigate the effects of z-yarns and interlaminar fracture toughness on delamination in woven composites. The results from the FE simulations revealed that z-yarns in 3D woven composites can play a major role in impeding propagation of interlaminar cracks. On the other hand 2D plain woven laminates without any z-reinforcement demonstrated higher interlaminar fracture toughness due to undulation in yarns. 3D woven composites with double yarns showed better damage tolerance than single yarn 3D woven composites and their behavior was very similar to composite laminates with high interlaminar fracture toughness. 相似文献
143.
When (robotic) Automated Fibre Placement (AFP) is used to manufacture aerospace components with complex three dimensional geometries, gaps between fibre tows can occur. This paper explores the interaction under compressive load of these tow gaps with impact damage. Two coupons with different distributions of tow-gaps were impacted. Results indicated that the area of delamination is smaller for an impact directly over a tow gap where the tow gap is situated close to the non-impact face. Subsequent Compression After Impact (CAI) testing demonstrated that both the formation of sublaminate buckles and subsequent growth of delaminations is inhibited by the presence of a tow gap near the nonimpact face. Non-destructive testing techniques and a computationally efficient infinite Strip model are used to analyse the damage resistance and damage tolerance of the coupons. A new validation of the Strip model is also presented. 相似文献
144.
A three-dimensional buckling delamination problem for a rectangular sandwich plate made from elastic and viscoelastic materials is studied. It is supposed that the plate contains interface embedded rectangular cracks and that the edge-surfaces of these cracks have initial infinitesimal imperfections. The evolution of these initial imperfections with an external bi-axial compressed force (for the case where the materials of the layers of the plate are elastic) or with duration of time (for the case where the materials of the layers of the plate are viscoelastic) is investigated. The corresponding boundary value problem is formulated within the framework of the piecewise homogeneous body model with the use of three-dimensional geometrically nonlinear field equations of the theory of viscoelastic bodies. This problem is solved by employing boundary form perturbation techniques, Laplace transform and FEM. According to the initial imperfection criterion, the values of the critical parameters are determined. Numerical results on the critical force and critical time are presented and discussed. In particular, it is established that the values of the critical forces obtained for the buckling delamination around the rectangular embedded interface cracks are significantly greater than those obtained for the corresponding edge and band cracks. 相似文献
145.
Arcady V. DYSKIN Elena PASTERNAK Yuri ESTRIN 《Frontiers of Structural and Civil Engineering》2012,6(2):188
We review the principle of topological interlocking and analyze the properties of the mortarless structures whose design is based on this principle. We concentrate on structures built of osteomorphic blocks – the blocks possessing specially engineered contact surfaces allowing assembling various 2D and 3D structures. These structures are easy to build and can be made demountable. They are flexible, resistant to macroscopic fractures and tolerant to missing blocks. The blocks are kept in place without keys or connectors that are the weakest elements of the conventional interlocking structures. The overall structural integrity of these structures depends on the force imposed by peripheral constraint. The peripheral constraint can be provided in various ways: by an external frame or features of site topography, internal pre-stressed cables/tendons, or self-weight and is a necessary auxiliary element of the structure. The constraining force also determines the degree of delamination developing between the blocks due to bending and thus controls the overall flexibility of the structure thus becoming a new design parameter. 相似文献
146.
147.
对Q345R钢板分层缺陷原因进行了研究。结果表明:分层缺陷钢板的夹杂物超标,且在钢板厚度方向存在明显的偏析线。分层处有明显的点列状孔洞分布,这是引起裂纹扩展的主要原因。钢板的基体组织为珠光体+铁素体,分层处组织为马氏体+少量贝氏体+少量铁素体。裂纹起源处的夹杂物为MnS和Al2O3且以MnS为主,沿着带状组织和夹层分布。分层处的断口形貌为解理断裂,呈片层状或羽毛状,断口有明显的分层现象。分层处的贝氏体、马氏体组织使材料脆性增加,在与MnS夹杂物的共同作用下,形成应力集中而产生裂纹。 相似文献
148.
149.
研究了碳纤维增强聚酰亚胺树脂基复合材料MT300/KH420的高温力学性能, 重点揭示了MT300/KH420的[0°]7、[0°]14 和[±45°/0°/90°/+45°/0°2]s层合板在常温~500 ℃的拉伸和层间剪切性能的变化规律。结果表明:在350 ℃以内,[0°]7层合板拉伸强度随温度升高有所提高, 拉伸模量几乎不变, 在420 ℃时拉伸强度和模量均出现明显下降, 在500 ℃时分别保持在65%和83%以上, 表现出优异的高温拉伸性能。MT300/KH420的[0°]14层合板层间剪切强度在常温~420 ℃随温度升高不断降低至52.8%, 在高温下呈现出黏弹效应, 且在420 ℃时最为明显。相比于单向层合板, [±45°/0°/90°/+45°/0°2]s多向层合板高温力学性能较为稳定, 且由纤维控制的纵向试件力学性能受温度影响较小。 相似文献
150.
为预测复合材料层合板的低速冲击特性,提出一种基于弹簧-质量模型的冲击分层响应模拟方法。首先根据假定的分层数量和分层面积计算分层前后的弯曲刚度与挠度变化,进而模拟出含分层过程的冲击头运动时间历程。然后,由冲击头的加速度计算接触力,并基于材料的弹-塑性接触定律计算出永久凹坑深度。随后,对共固化复合材料翼盒的壁板进行了低速冲击实验,冲击点分为3种类型:2个梁间蒙皮的中点位置、蒙皮与翼梁T型连接的胶接区边界和梁的正上方。接着,分析对比了不同冲击点的接触力、分层阈值力和凹坑深度的特点。最后,使用所提出的模型计算第1种冲击点的接触力、永久凹坑深度和吸收能量,并分析了矩形板长宽比对薄膜刚度及接触力的影响。结果表明:模拟的接触力与实测结果吻合良好,对永久凹坑深度和吸收能量的模拟精度也较高,所提模拟方法有效;随着长宽比的减小,薄膜刚度迅速增大,从而使接触力显著增大。 相似文献