Scaling Effects in Sublaminate-Level Scaled Composite Laminates
Scaling Effects in Sublaminate-Level Scaled Composite Laminates
复制标题
亚层压复合材料层压板中的缩放效应
作者：
D. P. Johnson;J. Morton;S. Kellas;K. Jackson
进行了一系列拉伸试验，以确定试样尺寸对复合材料层合板的力学响应的影响。研究的两种材料系统是AS 4/3502和APC-2。在AS 4/3502的情况下，考虑三种通用铺层：（±30/902 L）、（±45/0/90）™和（90/0/90/0）™ deg，其中n = 1、2、3或4。对于APC-2系统，只有（±45/0/90），，.使用n = 1和4研究DEG叠层。研究了试样尺寸对第一层失效应变、脱层起始应变、极限应力和应变的影响。在一般情况下，缩放试样的强度随着试样尺寸的增加而增加。应用文献中的模型试图解释观察到的变化。结果发现，铺层约束的影响是没有适当地解决在现有的理论。Kellas和Morton采用双级缩放，系统研究了试样尺寸对几种复合材料铺层拉伸响应的影响。2与许多脆性材料的行为一致，观察到强度随试样尺寸的增加而降低。随着试样尺寸的增加，强度退化在基体占主导地位的铺层中更为明显，其中离轴层片承载了大量的载荷。很明显，损伤（如基体开裂）的发生取决于层板厚度。5“13 Kellas和Morton 2指出，这种对层板厚度的依赖性是观察到的强度趋势的原因。在一项亚层压水平的比例研究中，3发现（±45/ ±45）nj deg层压板的第一层破坏应力和强度随着规格尺寸的增加而显著增加。强度的增加归因于随着层压板厚度的增加，两个弱表面层（第一层失效开始）的影响逐渐减小。由于剪切约束的减少，导致自由边缘处的面内、垂直于纤维的应力，第一层失效在表面层中开始。作为对早期层合板水平缩放研究的扩展，2目前的工作开始研究三个类似的通用铺层，这些铺层已经在子层合板水平缩放。考虑了两种碳纤维增强复合材料系统：AS 4/3502和APC-2，其由PEEK基质中的相同纤维（AS 4）组成。研究了使用石墨/环氧材料系统的三种铺层配置。由于资源有限，仅使用APC-2系统研究了一个铺层。选择准各向同性铺层。
A series of tensile tests has been performed to determine the effect of specimen size on the mechanical response of composite laminates that were scaled at the sublaminate level. The two material systems studied were AS4/3502 and APC-2. In the case of AS4/3502, three generic layups were considered: (±30/902L,, (±45/0/90)™, and (90/0/90/0)™ deg, where n = 1, 2, 3, or 4. For the APC-2 system, only the (±45/0/90),,.? deg layup was studied with n = 1 and 4. The effect of specimen size was examined with respect to first-ply failure strain, delamination onset strain, and ultimate stress and strain. In general, the strength of scaled specimens increased with increasing specimen size. Models from the literature were applied to attempt to explain the variations observed. It was found that the effect of ply constraint is not addressed properly in existing theories. A systematic study examining the effect of specimen size on the tensile response of several composite layups, employing ply-level scaling, has been presented by Kellas and Morton.2 In agreement with the behavior of many brittle materials, a strength degradation was observed with increasing specimen size. The strength degra- dation with increasing specimen size was more pronounced in the matrix-dominated layups where off-axis plies carry a significant amount of the load. It is clear that the onset of damage, such as matrix cracking, depends on ply thickness.5"13 Kellas and Morton2 stated that this dependence on ply thickness was responsible for the observed strength trends. In a sublaminate-level scaling study,3 it was found that the first-ply failure stress and the strength of (±45/ ±45)nj deg laminates increased significantly with increasing speci- men size. The increase in strength was attributed to the diminishing effect of the two weak surface plies (where first-ply failures initi- ated) as the laminate thickness increased. First-ply failure initiated in the surface plies due to the reduced shear constraint that led to in-plane, normal-to-the-fiber stresses at the free edge. As an extension to the earlier research on ply-level scaled laminates,2 the present work was initiated to study three simi- lar generic layups that have been scaled at the sublaminate level. Two carbon-fiber-reinforced composite systems were considered: AS4/3502 and APC-2, which consists of the same fiber (AS4) in a PEEK matrix. Three layup configurations using the graphite/epoxy material system were investigated. Because of limited resources, only one layup was investigated using the APC-2 system. A quasi- isotropic layup was chosen.