Research On Effects Of Non-Welded Area On Crack Growth Characteristic Of Diffusion Bonded Titanium-Alloy Laminates

Titanium alloys with excellent comprehensive performance such as high strength, strong durability, creep resistance, weldability, etc, has become the important material of the main structure of the aircraft and rocket. However, through the titanium alloy fatigue experiment research finding, no matter the whole pieces and the fission structure(welded or riveted) of titanium alloy, once fatigue crack initiation, the crack growth rate is fast, which is leading to titanium alloy component failure in a short time. This indicates that the damage tolerance performance of titanium alloys structure is poor and difficult to ensure that use safety, although the structure of the titanium alloy crack initiation life is long. Therefore, in order to improve damage tolerance, we need to study the design way of titanium alloy structure.This paper reports on the investigation of fatigue crack growth characteristics of diffusion bonded laminates of titanium-alloy with localized non-welded area under tension-tension cyclic loading using numerical simulation techniques based on extended finite element method (XFEM), and the influences of the geometric parameters, such as the number, positions and sizes of the non-welded areas, were analyzed and synthesized. The main researching contents were given as following.(1) The influence mechanism research of non-welded area on fracture properties of laminated structure. Titanium alloy laminated beam structure is selected as the research object. We calculate the crack tip stress intensity factor KⅠ and KⅡ under different crack length of the laminated beams with and without localized non-welded areas. The comparison and analysis on the curves of stress intensity factors vs crack length in the beams with and without localized non-welded areas shows that non-welded area can restrain the extension of cracks.(2)Analysis for Crack Growth Characteristic of Diffusion Bonded Laminates of Titanium-Alloy with Localized No-Welded Areas. Through discussing the availability of the finite element method (XFEM) in studying the fatigue crack growth characteristics, we prove that XFEM can get the exact crack growth characteristics by comparing the results of the simulation with the experiment. In addition, the influences of the crack growth characteristics along the surface, the depth and the projected area of fracture surface affected by the non-welded area are studied. And the results show that the non-welded area can obviously improve the damage tolerance of titanium alloy laminates. (3) Analysis of Parameters influencing Crack Growth Characteristic of Diffusion Bonded Titanium-Alloy Laminates with Localized Non-Welded Areas. The investigation of fatigue crack growth characteristics of diffusion bonded laminates of titanium-alloy with localized non-welded area using numerical simulation techniques based on extended finite element method (XFEM), and the influences of the geometric parameters, such as the number, positions and sizes of the non-welded areas, were analyzed and synthesized.