切口类型变化对复合材料双切口层间剪切强度的影响规律研究

利用三维有限元模型和试验对复合材料双切口试件层间剪切强度进行了研究,通过改变双切口试件的切口类型(标准双切口、半V型切口和V型切口),对比分析切口类型变化对试件剪切面应力水平、破坏模式和剪切强度的影响,对侧面夹具为Hopkinson金属棒的半V型切口试件剪切面应力水平进行了分析。结果表明,三种切口类型的试验都不是单纯、均匀的剪切强度试验:标准双切口(DNS)试件剪切面剪应力分布不均匀,横向压应力较大,它仅能得到复合材料的表观层间剪切强度;半V型切口(0.5DVS)试件剪切面剪应力分布最不均匀,横向压应力较小,所得剪切强度偏小;V型切口(DVS)试件剪切面剪应力分布最均匀,但横向压应力较大。DNS试件和0.5DVS试件破坏模式为单纯剪切破坏,两者所测剪切强度离散性相对较小,而DVS试件破坏时初始失效点不在剪切面上,存在二次失效,所测剪切强度离散性较大。综上所述,DNS试件最适合静态层间剪切强度测试。与含Hopkinson金属棒的试件相比,改变切口类型的试件之所以不能改善剪切面的应力水平,是由输入输出区刚度偏小造成的。

Study on the influence of notch type on composite interlaminar shear strength of double-notched specimen

The interlaminar shear strength of composite double-notched specimens is studied by threedimensional finite element model and experiment.By changing the types of notches(standard double notches,half V-notches and V-notches),the effects of the change of notch types on the shear stress level,failure mode and shear strength of the specimens are compared and analyzed.Afterwards,the stress of the half V-notched specimen with Hopkinson metal rod is analyzed.The results show that the three notch types of specimens are not involved in the pure and uniform shear strength tests:the shear stress distribution of standard double-notched specimens(DNS)is not pure,and the transverse compressive stress is large,which belongs to the apparent interlaminar shear strength test.The shear stress distribution of half V-notched specimens(0.5DVS)is the most uneven,and the transverse compressive stress is relatively small,resulting in relatively small shear strength.The shear stress distribution of V-notched specimens(DVS)is the most uniform,but the transverse compressive stress is relatively large.The failure modes of DNS and 0.5DVS are pure shear failure,and the discreteness of shear strength measured by DNS and 0.5DVS is relatively small.The initial failure point of DVS is not on the shear plane,and secondary failure exists,so the measured shear strength is more discrete.In conclusion,DNS with standard double notches are most suitable for static interlaminar shear strength testing.Compared with the specimens with Hopkinson bars,the fact that the stress level of shear plane can not be improved by changing the notch type is attributed to the small stiffness of input and output regions.