摘要
随着航空、核电、高铁、石油工程的发展,与工程安全密切相关的新型材料断裂疲劳性能及其获取方法研究受到了广泛重视,在获取材料断裂韧性的测试方法中,柔度法和载荷分离法已被国内外断裂测试规范列入推荐。鉴于现行规范中应用弯曲试样获取断裂韧性尚存在问题和欠缺,本文主要完成了如下工作：
(1)基于有限元精细分析提出了一套应用于直通型紧凑拉伸试样(front-face compact tension, FFCT)和三点弯曲试样(front-face single edged bending, FFSEB)加载线位移VLL与裂纹嘴张开位移V0之间的COD换算公式,新公式可用于非标准试样J积分塑性分量的计算,是金属延性材料断裂韧性国家测试标准(草案)最新推荐的方法要点。
(2)鉴于ASTM断裂韧性测试规范中推荐的载荷分离方法尚不能适用于FFCT和FFSEB试样且基础理论存在量纲不对等问题,本文提出了一套新的无量纲载荷分离表达式和相关公式,根据修正的载荷分离理论完善了用于FFCT和FFSEB试样的材料断裂韧性测试的载荷分离方法,基于FFCT试样实现了汽轮机低压转子材料1Cr12Mo、30Cr2Ni4MoV以及P91管材10Cr9Mo1VnBn三种材料的断裂韧性测试和JR阻力曲线测定；基于1/2TFFCT试样实现了A508-Ⅲ钢的断裂韧性测试；基于FFSEB试样实现了P91管材10Cr9Mo1VnBn的断裂韧性测试和JR阻力曲线测定。
(3)针对用于管道材料断裂韧性评定、具有低约束特性的单边裂纹拉伸(Single Edged Tension, SET)试样,建立了J积分的增量塑性功算式和塑性因子算式,提出了面向SET试样的无量纲载荷分离法,并应用新方法完成了汽轮机低压转子材料30Cr2Ni4MoV、电站用P92管道钢以及5083-H112铝合金SET试样断裂韧性值和J阻力曲线测定。
(4)基于有限元计算获得到了销钉式和夹持式SET试样的柔度计算公式。为了适应不同载荷形式和约束水平下SET柔度测试要求,对具有偏心为0.25W和0.5W的SET试样也给出了柔度计算公式。
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.
引文
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