Meo Michele, Rizzo Francesco, Portus Mark, Pinto Fulvio
Material and Structure Centre, Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK.
Materials (Basel). 2021 Sep 7;14(18):5133. doi: 10.3390/ma14185133.
Composite laminated materials have been largely implemented in advanced applications due to the high tailorability of their mechanical performance and low weight. However, due to their low resistance against out-of-plane loading, they are prone to generate damage as a consequence of an impact event, leading to the loss of mechanical properties and eventually to the catastrophic failure of the entire structure. In order to overcome this issue, the high tailorability can be exploited to replicate complex biological structures that are naturally optimised to withstand extreme impact loading. Bioinspired helicoidal laminates have been already studied in-depth with good results; however, they have been manufactured by applying a constant pitch rotation between each consecutive ply. This is in contrast to that observed in biological structures where the pitch rotation is not constant along the thickness, but gradually increases from the outer shell to the inner core in order to optimise energy absorption and stress distribution. Based on this concept, Functionally Graded Pitch (FGP) laminated composites were designed and manufactured in order to improve the impact resistance relative to a benchmark laminate, exploiting the tough nature of helicoidal structures with variable rotation angles. To the authors' knowledge, this is one of the first attempts to fully reproduce the helicoidal arrangement found in nature using a mathematically scaled form of the triangular sequence to define the lamination layup. Samples were subject to three-point bending and tested under Low Velocity Impact (LVI) conditions at 15 J and 25 J impact energies and ultrasonic testing was used to evaluate the damaged area. Flexural After Impact (FAI) tests were used to evaluate the post-impact residual energy to confirm the superior impact resistance offered by these bioinspired structures. Vast improvements in impact behaviour were observed in the FGP laminates over the benchmark, with an average reduction of 41% of the damaged area and an increase in post-impact residual energy of 111%. The absorbed energy was similarly reduced (-44%), and greater mechanical strength (+21%) and elastic energy capacity (+78%) were demonstrated in the three-point bending test.
由于其机械性能具有高度可定制性且重量轻，复合材料层压板已在先进应用中得到广泛应用。然而，由于它们对平面外载荷的抵抗力较低，在受到冲击时容易产生损伤，导致机械性能丧失，最终导致整个结构的灾难性失效。为了克服这个问题，可以利用高度可定制性来复制复杂的生物结构，这些结构自然经过优化，能够承受极端冲击载荷。受生物启发的螺旋层压板已经得到了深入研究并取得了良好的成果；然而，它们是通过在每个连续层之间应用恒定的螺距旋转来制造的。这与在生物结构中观察到的情况形成对比，在生物结构中，螺距旋转沿厚度方向不是恒定的，而是从外壳到内核逐渐增加，以优化能量吸收和应力分布。基于这一概念，设计并制造了功能梯度螺距（FGP）层压复合材料，以相对于基准层压板提高抗冲击性，利用具有可变旋转角度的螺旋结构的坚韧特性。据作者所知，这是首次尝试使用三角形序列的数学缩放形式来定义层压铺层，以完全复制自然界中发现的螺旋排列。对样品进行三点弯曲测试，并在15 J和25 J冲击能量的低速冲击（LVI）条件下进行测试，使用超声波测试来评估损伤区域。冲击后弯曲（FAI）测试用于评估冲击后的残余能量，以确认这些受生物启发的结构具有卓越的抗冲击性。与基准相比，FGP层压板的冲击性能有了大幅提升，损伤面积平均减少了41%，冲击后残余能量增加了111%。吸收能量也同样减少了（-44%），并且在三点弯曲测试中表现出更高的机械强度（+21%）和弹性能量容量（+78%）。
