Investigation On The Initial Fatigue Quality Of Welds Of Titanium Alloy Specimens

In advanced aircraft, titanium alloy use too much, because titanium alloy have good weld ability, and make structure reduce weight significantly, at the same time, save material, saving manufacturing costs, improve efficiency, its manufacturing process from originally of riveting to give priority to development welding primarily.Titanium alloy under high temperature chemical properties very lively, various complicated factors exist in the welding process, inevitably formed some welding defects, fundamentally eliminate welding defects in engineering is impossible. Therefore, the fundamental measures of prevent titanium alloy welding is damage tolerance design, therefore, must assess the initial fatigue quality to titanium alloy welding structure.The initial crack in damage tolerance design, is refers to put these initial defects that exist in the structure boils down to a nonentity equivalent faults size synthetically, called equivalent initial crack length and regard it as characterization of parameters, so the called equivalent initial faults size. Although a0i is a hypothetical crack length, but reflects the material quality and the manufacturing quality comprehensively, so a0i alternate name initial fatigue quality.Use the TC18, TC21, TC4, TA15titanium welding sample that in advanced aircraft has important application for research object, and applications of electron beam welding processed into fatigue specimen, carried out fatigue test in different test conditions.According to fatigue test sample fractography, and observations and statistical analysis have been made to titanium welding fatigue origin, fractography have two kinds that is pore and lack of penetration, fatigue origin mostly located in the specimen surface, If the samples have internal defects, the general fatigue crack initiation from defect place.Using fatigue striation and quantitative analysis by fractography to assess the initial fatigue quality. Firstly, using quantitative analysis method get extend life in different crack length, and we get life in different crack length, exactly(a, N) as foundation to initial fatigue quality evaluation, reuse (a, N) data trace out curve, fitted with the appropriate equation, get a0i, basis for get each initial fatigue quality, discuss distribution of the initial fatigue quality, the results show that the weibull distribution model and normal distribution is available to model the initial fatigue quality to titanium welding, and two models get close to the initial fatigue quality expected value.This paper also analyzed influence factors of initial fatigue quality, fatigue stress and defects are influence factors to initial fatigue quality, fatigue stress larger, initial fatigue quality a0i is larger also. Under near stress condition, defect size is larger, initial fatigue quality a0i also larger.