| In 1988, as a branch of computational mechanics, the computational fracture mechanics was proposed——a science which researches on the material structure containing the crack (flaw) by numerical method. The research fields include:(1) establishing mechanical and the mathematical model suitable for numerical calculation; (2) studying and creating high effective algorithm; (3) developing the software to solve fracture mechanics questions and the practical applications.Recent years, along with the rapidly developing of the computer science, mathematics and the mechanics and the breakthrough of high effective algorithm, the scientists have started to develop the softwares. Among them, FRANC2D/L and FRANC3D are powerful codes for fracture problems and have advantages in the simplicity of operation, moderately-price, powerful and have gradually been interested by researchers in its algorithm and the applications. For FRANC2D/L, the function is quite perfect because it processes the two-dimensional problem, and its research is much mature. However, the most engineering problems are three dimensional crack problems. Therefore, researches on FRANC3D are more valuable for engineering fracture problems.The main tasks of this article include:(I) Numerical calculation on stable crack tearing (mode I) is completed for Arcan specimens with two kind of thickness (6.35mm and 2mm) by using FRANC2D/L1) The effect of FRANC2D/L's mesh technology on the calculation result is researched. It is suggested that this software's initial grid division has little effect on the results, and quite precise result can also be obtained with relatively rough grid. The crack surface's grid density has great effect on the computed results before the load reaches to its capacity, while it has little effect on them after the load reaches to its capacity. When the crack surface's unit size is consistent with fracture growth's element size (0.508mm), very good computational accuracy can be obtained.2) Effective stresses and plastic zone at crack tip of aluminum alloy plates with the different thickness and welding parameters are analyzed. It is suggested:a) the yield stress is bigger, the size of plastic zone at crack tip is smaller, b) the shape of plastic zone is infected with the thickness or the boundary of plate, c) the size of plastic zone increases first, then tends to be invariable along with the growth of crack length, d) The plastic zone of crack for initiation reduces along with thickness increasing, and keeps constant finally.(Ⅱ) Numerical calculations on several examples with penetrating crack, internal crack and surface crack are studied by using FRANC3D. The effect of the exterior grid density, the crack surface grid density and the element shape function on accuracy of SIF is analyzed. It is indicated that:a) the crack surface's grid division has great effect on the computed results. When crack surface is divided with the proportion 1:4, a higher precision may be obtained. b) the exterior grid density has little influence on the SIF's computed result. c) in calculation, the quadratic shape function for a element shall not be used as possible as you can; the same precision will be obtained quickly with the linear shape function. Researches on tons of examples indicated that the error of SIF between the calculative value and the theoretical value by this software maintains in 5%, which proved the reliability of the FRANC3D software.(Ⅲ) The K-a relations, the COD cloud chart and the fracture growth path (shape) has been numerically studied for everal stable crack tearing examples with penetration crack, internal crack, surface crack by using FRANC3D. The result indicated that the simulation of fracture growth is viable.
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