Riccio Aniello, Russo Angela, Sellitto Andrea, Toscano Cinzia, Alfano Davide, Zarrelli Mauro
Department of Engineering, University of Campania "L. Vanvitelli"-via Roma, 81031 Aversa, Italy.
CIRA Italian Aerospace Research Centre, Via Maiorise s/n, 81043 Capua, Italy.
Polymers (Basel). 2020 Mar 3;12(3):554. doi: 10.3390/polym12030554.
Increasing the Mode I inter-laminar fracture toughness of composite laminates can contribute to slowing down delamination growth phenomena, which can be considered one of the most critical damage mechanisms in composite structures. Actually, the Mode I interlaminar fracture toughness () in fibre-reinforced composite materials has been found to considerably increase with the crack length when the fibre bridging phenomenon takes place. Hence, in this paper, the fibre bridging phenomenon has been considered as a natural toughening mechanism able to replace embedded metallic or composite reinforcements, currently used to increase tolerance to inter-laminar damage. An experimental/numerical study on the influence of delamination growth on the compressive behaviour of fibre-reinforced composites characterised by high sensitivity to the fibre bridging phenomenon has been performed. Coupons, made of material systems characterised by a variable toughness related to a high sensitivity to the fibre bridging phenomenon and containing artificial through-the-width delaminations, were subjected to a compressive mechanical test and compared to coupons made of standard material system with constant toughness. Out-of-plane displacements and strains were monitored during the compression test by means of strain gauges and digital image correlation to assess the influence of fibre bridging on delamination buckling, delamination growth and on the global buckling of the specimens, including buckling shape changes. Experimental data were combined with a numerical study, performed by means of a virtual crack closure technique based procedure, named SMart Time XB - Fibre Bridging (SMXB-FB), able to mimic the crack bridging effect on the toughness properties of the material system. The combination of numerical results and experimental data has allowed the deformations and the buckling shape changes to be correlated to the onset and evolution of damage and, hence, contributes to improving the knowledge on the interaction of the failure mechanisms in the investigated composite specimens.
提高复合材料层压板的I型层间断裂韧性有助于减缓分层扩展现象，分层扩展现象可被视为复合材料结构中最关键的损伤机制之一。实际上，当发生纤维桥接现象时，纤维增强复合材料中的I型层间断裂韧性（）已被发现会随着裂纹长度的增加而显著提高。因此，在本文中，纤维桥接现象被视为一种天然的增韧机制，能够替代目前用于提高层间损伤耐受性的嵌入式金属或复合材料增强材料。针对对纤维桥接现象高度敏感的纤维增强复合材料，开展了一项关于分层扩展对其压缩行为影响的实验/数值研究。由对纤维桥接现象高度敏感且韧性可变的材料体系制成、并含有贯穿宽度的人工分层的试样，进行了压缩力学试验，并与由具有恒定韧性的标准材料体系制成的试样进行了比较。在压缩试验过程中，通过应变片和数字图像相关技术监测面外位移和应变，以评估纤维桥接对分层屈曲、分层扩展以及试样整体屈曲（包括屈曲形状变化）的影响。实验数据与通过基于虚拟裂纹闭合技术的程序（名为SMart Time XB - 纤维桥接（SMXB - FB））进行的数值研究相结合，该程序能够模拟裂纹桥接对材料体系韧性性能的影响。数值结果与实验数据的结合使得变形和屈曲形状变化能够与损伤的起始和演变相关联，从而有助于增进对所研究复合材料试样中失效机制相互作用的认识。
