【作者】 包陈；

【导师】 蔡力勋；

【作者基本信息】 西南交通大学 ， 固体力学， 2011， 博士

【摘要】 随着航空、高速铁路、化工、反应堆工程等的飞速发展,材料断裂性能的工程需求在新世纪迅速扩大。然而,传统断裂力学测试在载荷分离法、柔度法、测试标准的有效应用等方面仍存在一系列问题,一些问题仍具有突出的理论研究与工程应用价值。单轴应力应变曲线的便携测量对于实现工程构件材料力学性能的在役检测意义深远,基于硬度技术的压入法在该领域显示了良好的应用前景,但是现有方法尚不成熟,需要进一步完善。本文对材料断裂测试中的载荷分离法、柔度法以及基于压入技术的单轴应力应变曲线获取方法进行了深入系统的研究,重点完成了如下工作：1.基于相似理论提出了无量纲化载荷分离理论,解决了现行载荷分离理论的量纲不对等问题。基于无量纲化载荷分离理论,发展了改进的分离参数Spb法,新方法有效消除了参考钝裂纹和标定点选择对试样裂纹长度预测的影响。应用新方法完成了Cr2Ni2MoV钢、A508-Ⅲ钢以及输气管道球阀焊接接头等工程材料的JIC、CTOD和CTOA测定,新方法的有效性和实用性得到了验证。根据对ASTM现行规范中载荷分离法的深入研究与创新进展,为金属材料准静态断裂韧度统一试验国家标准新版修订提出了增订的载荷分离法附录草案。2.对柔度测试中现行转动修正方法存在的问题进行了细致研究,基于刚性铰链假设和功等效原理提出了适用于CT、SEB和SET三类试样的柔度转动修正方法。研究结果表明,由弹塑性有限元分析提出的三类试样转动半径计算公式比现行规范公式更为合理和有效；刚性转动对试样裂纹长度的柔度计算不产生附加影响,但对J积分计算结果的影响显著；对于在加载点测量位移的SEB试样无需进行柔度转动修正；在采用柔度法完成JIC测试时,合理的做法是仅对载荷-位移测量曲线进行柔度转动修正,无需对预测裂纹长度的测量柔度进行转动修正。对SEB试样和直通型CT试样提出了裂纹嘴张开位移同加载点(加载线)位移的弹塑性换算公式,使得从裂纹嘴张开位移测量中获得材料断裂韧性JIC有效可行,进而确保了现行材料断裂韧性测试标准在该技术领域的完整性。3.对SEB试样和CT试样提出了测算裂纹长度和等效弹性模量的统一简化公式；修正了柔度法中塑性J积分增量迭代算式的不合理内容；为方便焊缝、复合材料等特殊分层材料的断裂性能测试,基于有限元分析提出了分层结构CT试样的柔度方法；提出了用于断裂性能测试的点触式高温柔度法,拓展了柔度法在高温测试环境中的应用；对不同版本的JIC和CTOD现行断裂测试标准进行了详细的差异比较,选取典型材料研究了不同测试标准对材料断裂性能评价的影响；基于柔度法的系统创新进展,提出了金属材料准静态断裂韧度统一试验国家标准新一轮修订版本中关于柔度法的推荐附录草案。4.基于压入试验技术,发展了直接从球形压头载荷-压入深度曲线中获得材料单轴应力应变曲线的方法；根据A533-B钢、C40钢、316L不锈钢、退火Cu、0Cr18NiTi不锈钢和A105钢等材料的压入试验结果,新方法的有效性得到了验证。更多还原

【Abstract】 With rapid development of aviation, high-speed railway, chemical engineering and reactor engineering, the engineering demand for the fracture properties of materials has been evidently expanded in the new century. However, there still exist a series of problems of load separation method, unloading compliance method, and the effective application of fracture test standards in the traditional fracture mechanics testing. Some issues still have highlighted the value of theoretical research and engineering application. Portable measurements of uniaxial stress versus strain curves have significant impact on the inservice inspection of engineering components. Fortunately, the indentation technique on the basis of hardness testing presents good prospects in this field. However, some improvements are needed for this method because of less effective applications in the existing researches. This thesis systematically carried out researches on the load separation method, unloading compliance method, the determination of uniaxial stress-strain curves by spherical indentation technique. The main works are introduced as follows:1. Based on similarity theory, a nondimensional load separation principle is proposed, so the dimensionless asymmetry problem in the current load separation principle has been solved. Correspondingly, a modified load separation parameter Spb method is developed according to the nondimensional load separation principle. This new method diminishes the effect of the reference blunt crack specimen and the choice of calibration points on the crack length determination of sharp crack specimen. Experiments on the determination of JIc for Cr2Ni2MoV and A508-Ⅲsteel, the estimation of CTOD for welded joints of certain gas pipeline ball valve and the estimation of CTOA for A508-Ⅲsteel are completed by use of the modified load separation parameter Spb method, and the validity of this method is successfully certified. According to researches on load separation method, a draft of corresponding appendix for the new national and unified test standard for quasistatic fracture toughness is given.2. Detailed investigation on the problems of current rotation correction method for CT specimen is conducted, then new reasonable rotation correction methods for CT, SEB and SET specimens are developed on the basis of rigid hinge hypothesis and work equivalence principle. The results show that, the rotational radiuses of the three types of specimens obtained by elastic-plastic finite element analysis are more reasonable than the current results. The rigid rotation has little effect on the measurement of crack length, but the J-integral computation is seriously affected. For SEB specimen, the rotation effect can be ignored when the displacement is measured at the load point. When using unloading compliance method to determine JIC, a reasonable approach is to correct the measured load versus displacement records firstly, but not correct the measured compliance directly. Based on the new rotation correction method, elastic-plastic transforming formulas between crack mouth opening displacement and load point/load line displacement for SEB specimen and straight-notch CT specimen are proposed, respectively. These formulas are feasible for the JIC determination on the basis of crack mouth opening displacement measurements, and the defect of current fracture testing standards in this field has been made up.3. In unloading compliance method, unified and simplified formulas for the crack length measurement for both SEB and CT specimens are proposed when the displacements are measured at different location of specimens, and thus simplified formulas for effective elastic modulus are deduced correspondingly. An unreasonable expression for the incremental iteration of plastic J-integral is corrected. Based on finite element analysis, a compliance method for a CT specimen with layered structure is developed, which is benefit to the fracture test for some special materials such as welded joint. In order to expand the application of compliance method in high-temperature fracture testing, a point-touch high-temperature compliance method is developed. The differences for various versions of JIC and CTOD test standards are discussed in detail, and some typical metallic materials are employed to investigate the influence of different test standards on the evaluation of fracture toughness. According to researches on unloading compliance method, a draft of corresponding appendix for the new national and unified test standard for quasistatic fracture toughness is given.4. Based on spherical indentation technology, a direct method to estimate the uniaxial stress-strain curves from the load versus indentation depth records is developed. Consequently, the validity of this method is successfully certificated by some indentation tests for A533-B steel, C40 steel,361L stainless steel, annealed Cu, OCr18NilOTi stainless steel, and A105 steel.更多还原