碳/环氧典型层合板的疲劳试验和寿命估算

Fatigue Life Prediction for Typical Composite Laminates

报导了碳纤维/环氧T300/QY8911典型层板[0]_(16)、[90]_(20)、[0/90]_(4s)和[0/±45/90]_(2s)拉-拉疲劳试验结果,应力比R=0.05,最大应力值选几种水平,加载频率f=15 Hz.试验过程中测定了试件刚度变化情况,建立了对数形式的拟合方程.针对不同层板的断口形貌和刚度消减情况,提出了相应的损伤模型和寿命估算公式.这些公式可进一步发展用来估算同种材料做成的各种层合板在拉一拉载荷作用下的寿命.

Up to now past research on fatigue behavior of composite laminates generally centered on stiffness reduction and could not predict fatigue life. Starting from stiffness reduction, the authors propose an improved model that can predict fatigue life agreeing with test data. Tension-tension fatigue test results of typical composite laminates, [0]_(16), [90]_(20), [0/ 90]_(4) and [0/±45/ 90]_2,are presented in the paper. All of these laminates are laid by T300/ QY8911 carbon/ resin unidirectional prepreg. The same stress ratio, R=0.05, and several different maximum stress levels are selected for each kind of tested speciments. In the improved model, it is considered that nonuniform stress distribution in fibres as well as fibre fracture caused by microcrack in resin and initial waviness of fibre will control the fatigue failure of unidirectional ply. Fatigue life is directly related to its longitudinal strength σ_(ut). The formula, σ_(max) / σ_(ut)=A-BlgN_o, is proposed for evaluating fatgue life. A modified way can consider bridge effect on fatigue life of laminates consisting of plies with different orientations. Briefly, the new longitudinal strength of 0° ply evaluated by [0/ 90]_s static strength and Tsai-Hill criteron will replace the former σ_(ux) and give a value of N_o that agrees rather well with test data. For the case of laminate that suffers from interlaminar damage, its fatigue is prelimi narily estimated as the sum of two parts: (Ⅰ) N_1, which is the fatigue life for the laminate whose layers are all seperated. The full paper gives a somewhat crude method for estimating N_1 (2) N_2, which is the life corresponding to just the 0° ply failure in laminate. The estimated life, (N_1+N_2), is higher than experimental data by about 68%.