Prestressed Ceramics And Layered Ceramic Composite Materials, Stress Analysis And Design,

Residual stress plays an important role in both failure and strengthening of engineering materials. Although laminated ceramic composite has been extensively researched during past years, accurate calculation and measurement of residual stress in the composite materials has not been developed perfectly. The theoretical analysis and testing on residual stress involve an intersection of materials science, mechanics and applied physics. This study aims to searching a solution for some problems in the intersection.Because of the difference of thermal expansion coefficients between adjacent layers, residual stresses would be induced in laminated ceramics when it's cooled from high temperature to room temperature in fabrication process. In this study, residual stresses in the laminates with strongly bonded interface were investigated because strongly bonded interface results in high residual stress. An uneven strain model was established to quantitatively and qualitatively analyze the distribution of residual stresses and interface stresses. It's demonstrated that the residual stress is a function of the location along length direction of bar specimen. It was pointed out and confirmed that the normal stress can occur at interface in many cases. An analytical formula with concise form was represented for stress calculation. On the basis of this model, an optimization design rule of ceramic laminates with strong interface was derived.Al2O3/Ti3SiC2 and Al2O3-ZrO2/Al2O3-ZrO2 multi-layered composite were studied experimentally. Several basic rules obeyed in process of fabrication of laminates with strongly bonded interface were found. The relationships between strength, modulus, fracture energy et al and geometrical factors such as ratio of layer thickness, numbers of layers were investigated by means of bending tests. The results indicate that the optimum radio of layer thickness is related with geometrical structure and elastic constants of materials. The optimum value of ratio of thickness of three-layered A-10Z/A-30Z was found between 2.49 and 4.45, at which the bend strength of 867MPa was obtained that is about two times of that in homogeneous A-10Z. It was revealed that the laminate with three or five layers, relatively, possesses the optimum strength property, further increase of layer numbers might lead to degradation of strength. Above results experimentally confirm the optimum design rule.Distribution of residual stress was investigated by observing the change of indentation crack sizes at parallel and normal directions in laminated bar. The resultsindicate that the experimental value is fairly consistent with the calculated value. Damage behavior of A-10Z/A-30Z and A/TSC laminates was analyzed using sphere indentation and the local strength and residual stress were evaluated.Elastic modulus and plasticity of A-10Z/A-30Z and A/TSC laminates at high temperatures were measured using 3-point bending cyclic load. The effects of initial level of stress, temperature, laminated structure on stress relaxation and creep behavior of the laminates were studied. The results indicate that the stress relaxation and creep of laminates depend on the layer with relatively weak high temperature properties.The research on the pre-stressed Al2O3/aluminium alloy indicates a great practical value of pre-stressed laminates for bulletproof and resistance of armour-piercing. This is a main attempt for the application of laminated ceramics with pre-stress.