The Fracture Toughness Testing Methods Of Non-standard Specimens And Their Application

With the development of key engineerings such as aviation, nuclear power, high-speed railway and petroleum transportation, fatigue and fracture properties of materials and their testing methods attract wide attention. Compliance method and load separation method as advanced test technologies in the field of testing fracture toughness have been recommended by international and national fracture test standards. Considering the problems or difficulties existing in current standards for non-standard specimens, the main works carried out in this thesis are as follows:(1) Based on the refined results of the relationship between crack opening displacement (COD) along load line and crack mouth opening displacement (CMOD) obtained from finite element analysis (FEA), the COD transform formulas used for calculating plastic work of J integral for front-face compact tension (FFCT) specimens and front-face single edged bending (FFSEB) specimens are proposed respectively. As a key method point, it has been recommended to the national fracture toughness test standard of ductile materials.(2) Since the load separation method recommended by ASTM material fracture toughness test standard has the dimensional issue and it can not be applied for FFCT and FFSEB specimens, an improved load separation method is presented according to the dimensionless principle. A series of tests of FFCT and FFSEB specimens for1Cr12Mo,30Cr2Ni4MoV, A508-Ⅲ steel and10Cr9MolVnBn ware carried out, and the J-resistance curves and fracture toughness properties of the materials ware obtained by the improved load separation method.(3) In view of low constraint properties, SET (Single Edged Tension) specimens are gradually applied for the assessment on fracture toughness of pipe materials. The non-dimensional load separation method to estimate J resistance curves of materials for SET specimens is proposed, and30Cr2Ni4MoV used for steam turbine low pressure rotors, T92pipe steel and5083-H112aluminum alloy are employed to experimentally complete the estimation of J resistance curves by using the new method.(4) For both pin-loaded SET specimen and clamped SET specimen, the suitable FEA models are built to obtain the compliance formulas. In order to meet demand of compliance tests for SET specimens under different loading and bound conditions, the compliance formulas for the specimens with0.25W and0.5W bias were given separately.