Development of Testing Method for Mixed Mode Stregth of Bonded Interface and Composites

建立了复合材料与粘结非均质界面混模强度的测试方法。陶瓷/金属或不同金属的粘结界面是由于力学性能和热膨胀性能的不同而产生的具有力学奇异性的特殊界面。由于非均质性，使用中的这种界面同时承受着法向应力和剪应力。剪切应力分量的存在对界面强度有很大的影响。纤维增强复合材料中的情况应该是相同的，因为FRP或FRM的强度预计会受到纤维与基体之间界面强度的影响。在常规的四点剪切试验的基础上，发展了复合材料和界面的混合模式试验。新研制的四点剪切试验机是为了在小尺寸试件上评价界面或复合材料的剪切强度。对不同碳纤维类型、PAN类型和Mehto相沥青类型的CFRP和CFRM进行了不同加载方向、不同纤维方向的拉伸、弯曲和压缩试验。利用扫描电子显微镜油液伺服试验机，对CFRM进行了现场抗压断裂过程的现场观察，并结合四点剪切试验中的剪切强度，对CFRM进行了热处理，分析了各种强度类型和断裂过程。四点剪切试验得到的界面剪切强度表明，由于纤维和热历史的不同，界面对界面脱屑具有很高的敏感性，并与复合材料的拉伸和压缩强度密切相关。因此，四点剪切试验的剪切强度是衡量纤维增强复合材料和非均质界面强度的有效指标。

Testing method for mixed mode strength of composites and bonded heterogeneous interfaces has been developed. Bonded interface of ceramics/metals or different metals is a particular interface with mechanical singularity due to differences in mechanical properties and thermal expansion. Such interfaces in service are subjected to simultaneously normal and shear stress due to the heterogeneity. The presence of shear stress component should have strong influence on the strength of the interface. The situation in fiber reinforced composites should be the same, because the strenght of FRP or FRM are expeted to be affected by the strength of interface between fiber and matrix. Mixed mode testing thus for composites and interfaces has been developed through an application of conventional 4 points shear testing.The 4 points shear testing apparatus was newly developed to evaluate shear strength of interfaces or composites in small size specimen. Tensile test, bend test and compressive test for various loading direction with different direction of fiber were carried out for CFRP and CFRM with different type of carbon fibers, PAN type and mehto-phase pitch type. In-situ obsevation of fracture process in compressive test was tried using oil servo type testing equipment in SEM.In order to vary the interface strength, thermal heat treatment was applied to CFRM.Various types of strength and fracture process were analyzed with reference to the shrear strength in the 4 points shear test. The shear strength of interface obtained in the 4 points shear test indicates high sensitivity to degaradation of interface due to differences in fiber and thermal history, and demonstrates close relation with tensile and compressive strength of composites. It is, therefore, concluded that the shear strength in 4 points shear tests must be an useful measure of the strength of fiber reinforced composites and heterogeneous interfaces.