Abstract

Composite sandwich panels are commonly considered as lightweight materials for structural design in many applications including automotive, aerospace and defence systems. These panels must be developed and validated for its mechanical strength characteristics under different loading conditions before deploying them for the practical application. Hence, the present paper deals with the experimental and numerical studies on composite sandwich panels subjected to quasi-static edgewise and flatwise compression loads. The composite face sheet was developed using 2 × 2 bi-directional 200GSM twill carbon fibre with hot cure benzoxazine resin. Sandwich panels were made using the developed composite face sheets with aluminium honeycomb core. The developed composite face sheets were tested for tensile and flexural conditions and the sandwich panels for edgewise and flatwise compression loads. Three samples for each of these tests were conducted in Shimadzu UTM with 50 kN capacity machine. A consistent load-displacement profile and the failure pattern were observed for all the samples tested in each test category. It is noted from these tests that the composite face sheets exhibited an ultimate tensile strength of 444 MPa and a flexural strength of 842 MPa which is pretty to close to the epoxy based composites used in the aerospace applications; sandwich panels showed an edgewise compressive strength of 610 MPa and flatwise compressive strength of 3.5 MPa. Tensile test coupons initially had undergone certain delamination before failure and failed close to the specimen holding end. Flexural test specimens were shown delamination of only one layer at the loading face. However, the specimen was well intact together even after failure. Bending mode of failure was noted during edgewise compression test of the sandwich; severe delamination was seen in the tension side of the sandwich whereas a line-folding crack with failure was exhibited at the mid-plane of the specimen. In case of flatwise compression, no evident of damage was observed in the sandwich structure. The second part of the paper describes the numerical simulations of these test cases including tensile, flexural, edgewise compression and flatwise compression using an explicit finite element solver viz. LS-DYNA. Material type 22 and 26 was selected to define the material behaviour of composites and honeycomb respectively. The delamination was modelled using *CONTACT_AUTOMATIC_SURFACE_SURFACE_TIEBREAK card with option 9 that works under B-K linear fracture mechanics law to define the normal and shear failure of cracks. The numerical results were found to match well with experimental observations for the individual coupons as well as the sandwich samples. Therefore, it is concluded from this study that the developed LS-DYNA simulation methodology can be used as a tool for composite sandwich panels based lightweight structural design.

摘要

复合夹芯板通常被认为是许多应用中结构设计的轻质材料，包括汽车、航空航天和国防系统。在将它们部署到实际应用之前，必须开发和验证这些面板在不同负载条件下的机械强度特性。因此，本文处理了复合夹芯板受到准静态边缘和平面压缩载荷的实验和数值研究。复合面板是使用 2×2 双向 200GSM 斜纹碳纤维和热固化苯并恶嗪树脂开发的。夹心板是使用开发的带有铝蜂窝芯的复合面板制成的。对开发的复合材料面板进行拉伸和弯曲条件测试，并对夹层板进行边缘和平面压缩载荷测试。每个测试的三个样品在 Shimadzu UTM 中使用 50 kN 容量的机器进行。在每个测试类别中测试的所有样品都观察到一致的负载位移曲线和失效模式。从这些测试中可以看出，复合材料面板的极限拉伸强度为 444 MPa，弯曲强度为 842 MPa，非常接近航空航天应用中使用的环氧基复合材料；夹芯板的边缘抗压强度为 610 MPa，平面抗压强度为 3.5 MPa。拉伸试样最初在失效前经历了一定的分层，并在接近试样夹持端时失效。弯曲测试样品在加载面上仅显示出一层分层。然而，即使在失败之后，样本也完好无损。在夹层的边缘压缩试验中注意到弯曲失效模式；在夹层的受拉侧观察到严重的分层，而在试样的中平面则出现折线断裂并失效。在平面压缩的情况下，在夹层结构中没有观察到明显的损坏。本文的第二部分描述了这些测试用例的数值模拟，包括使用显式有限元求解器即拉伸、弯曲、边缘压缩和平面压缩。LS-DYNA。选择材料类型 22 和 26 来分别定义复合材料和蜂窝的材料行为。使用带有选项 9 的 *CONTACT_AUTOMATIC_SURFACE_SURFACE_TIEBREAK 卡对分层进行建模，该卡在 BK 线性断裂力学定律下工作，以定义裂纹的法向和剪切破坏。发现数值结果与单个试样和三明治样品的实验观察结果非常吻合。因此，本研究得出结论，开发的 LS-DYNA 仿真方法可以用作基于复合夹芯板的轻质结构设计的工具。