316L三点弯曲试样动静态断裂韧性对比实验研究

为研究316L型不锈钢的动静态断裂韧性,该文使用Instron-4505万能材料试验机对含有预制裂纹的316L型不锈钢试样进行准静态三点弯曲实验,测得其准静态断裂韧性应力强度因子K_I=53.34 MPam,同时基于霍普金森压杆(SHPB)技术对该材料三点弯曲试样进行动态断裂韧性的实验研究,测得其在3种不同加载率下的动态断裂韧性应力强度因子。结果表明:316L型不锈钢是率敏感材料,随着加载率的增加,该材料的动态断裂韧性呈下降趋势,且其断裂力学性能优良,可在工程实际中广泛应用。     

薄壁圆筒试样的扭转断裂曲线

通过比较多种材料的光滑薄圆筒和切口薄壁圆筒试样的扭断裂曲线，测向两种试验的断裂韧性ＫＩＩＣ相同，从而间接证实了利用光滑薄壁筒测定延性金属断裂韧性ＫＣ方法的正确性。     

聚醚酰亚胺对氰酸酯树脂/环氧树脂共混物的增韧作用

采用聚醚酰亚胺以提高双酚Ａ二氰酸酯／酚醛环氧树脂共混物的断裂韧性．实验结果表明，聚醚酰亚胺是氰酸酯／酚醛环氧树脂共混物的有效增韧剂，加入１５％的聚醚酰亚胺可使断裂韧性（ＫＩＣ）提高到１４５ＭＰａ·ｍ０．５，弯曲强度也有所提高．用扫描电子显微镜和动态粘弹谱研究了改性共混物的微观结构，具有双连续结构的共混物的耐溶剂性能大大下降，共混物的韧性和耐溶剂性主要与相行为有关， 固化工艺对含１０％聚醚酰亚胺的共混物的断裂韧性和形态没有明显的作用．     

层板复合材料动态断裂韧性测试的SHPB技术研究

为测试层板复合材料的断裂韧性，对传统的Hopkinson压杆测试系统进行了改进，建立了应力波载荷作用下材料动态断裂韧性的测试方法。该方法采用三点弯曲试样进行动态断裂试验，应用动态断裂韧性测试系统ANSYSED5．4确定动态应力强度因子的响应曲线，进而测试材料动态断裂韧性。对层板复合材料试验结果的分析表明，设计的测试装置有效，建立的测试方法是对层板复合材料断裂韧性测试的有益尝试，有较大的参考价值。     

极化电场取向对应力诱发PZT畴转向增韧的影响

研究了ＰＺＴ压电陶瓷断裂韧性Ｋ１ｃ随温度、特别是铁电相变的变化。探讨了极化电场与外应力的相对取向对材料Ｋ１ｃ的影响。结果表明，断裂韧性随温度升高而下降至居里点处的最低值，然后略有回升。基于裂纹尖端应力诱发畴转向的增韧机理，极化取向垂直于外张应力时的Ｋ１ｃ比平行取向的高。     

泡沫夹层复合材料耐水性能研究进展

泡沫夹层复合材料作为一种新型轻质高强材料，目前越来越受到航天、航海及能源等领域的重视，但其应用大部分仍局限于次级结构，主要是由于其可靠性评价未得到广泛深入研究。概述了其吸水性能、吸水后静态和动态力学性能及断裂韧性变化规律，最后提出了防水措施。     

具有高精度静态和快速动态测量能力的多路系统

具有高精度静态和快速动态测量能力的多路系统Ｍ．Ｋｒｅｕｚｅｒ１．前言本文描述了一个能同时完成两种任务的多路系统，它既适合干高速动态测量又适合于高精度的高分辨率静态测量。该系统是基于新的ＡＤＣ原理，能将模拟信号转换成快速数字数据量而不损失分辨率和带宽信...     

一种可切削玻璃陶瓷的压痕断裂特性

将断裂韧性测试的压痕方法与压痕弯曲方法相结合，独立地分离出了压痕残余应力因子ｘ，使其成为可测参量，并建立了压痕一压痕弯曲的断裂韧性测试方法．将这种方法应用于一种可切削玻璃陶瓷的测试，获得的Ｋ１ｃ值为Ｋ１ｃ＝２．０３ＭＰａ·ｍ１／２，与单边切口法（ＳＥＮＢ）获得的Ｋ１ｃ值有较好的一致性．测得的残余应力因子Ｘ＝０．０９３，符合Ａｎｓｔｉｓ经验公式的预测．     

高强度钢动态冲击疲劳性能的研究与应用

对高强度钢ＨＱ－６０和ＨＱ－８０的动态冲击疲劳性能作了全面的试验研究，测定了两种材料的冲击疲劳性能曲线，即能量－寿命曲和和冲击疲劳下的裂纹扩展速度ｄａ／ｄＮ，以及动态断裂韧性ＫⅠｄ等。结合１５４ｔ电动轮自卸车的车架强度和寿命校核，提出了一种新的应用模型，为受冲击疲劳型载荷的零部件找到了一种实用的校核计算方法，具有普遍的推广应用价值。     

2024-T3铝合金的动态断裂韧性

目的实现2024-T3铝合金动态断裂韧性的测量,揭示加载速率对动态断裂韧性的影响机理。方法采用屏蔽措施避免电磁干扰,测量2024-T3铝合金在不同加载速率下的动态断裂韧性,采用扫描电子显微镜(SEM)观察断口形貌,理论分析加载速率对动态断裂韧性的影响机理。结果当加载速率小于103MPa·m~(1/2)·s~(-1)时,2024-T3铝合金的动态断裂韧性约为35 MPa·m~(1/2);当加载速率高于105 MPa·m~(1/2)·s~(-1)时,动态断裂韧性超过40 MPa·m~(1/2),且随加载速率的增加而不断增大至101 MPa·m~(1/2)。断口分析表明,加载速率较低时,断口形貌为微孔聚集型;当加载速率超过105 MPa·m~(1/2)·s~(-1)时,断口特征由延性韧窝向准解理形态转变。理论分析表明,上述现象主要是由于裂纹尖端的无位错区域尺寸随加载速率的增大而减小,位错对裂纹尖端应力场的屏蔽效应增大,从而导致裂纹起裂后迅速由韧窝状态向准解理状态转变。结论电磁屏蔽后的电阻应变片法,能够准确测量电磁环境下2024-T3铝合金的动态断裂韧性,且动态断裂韧性表现出明显的应变率敏感性;2024-T3铝合金的微观断裂机制在准静态下为微孔聚集型,加载速率超过105MPa·m~(1/2)·s~(-1)时,材料的断裂表现为由延性韧窝形态向准解理形态转变。     

SENB 方法中 K_(1c)的修正与尺寸效应

单边切口梁(SENB)法是测试脆性材料断裂韧性 K_(?)的最通用而简便的一种方法,但它在理论上还不够完善。本文分析了试样尺寸对 K_(lc)测试值的影响,导出了不同尺寸比例试件的 K_(lc)之间的关系式。并发现对应于临界尺寸下 K_(lc)测试值是最大值,约为真实值的1.2倍。对氧化铝和氮化硅两种工程陶瓷进行了尺寸效应的试验,得到的结果与理论分析完全一致。     

A method for testing interlaminar dynamic fracture toughness of polymeric composites

Static and dynamic Mode I delamination fracture in two polymeric fiber composites was studied using a WIF test method. The dynamic test was conducted on a Split Hopkinson Pressure Bar apparatus. Crack speeds up to 1000 m/s were achieved. Dynamic fracture and crack propagation were modeled by the finite element method. Dynamic initiation fracture toughness of S2/8552 and IM7/977-3 composites were obtained. The dynamic fracture toughness of IM7/977-3 associated with the high speed propagating crack was extracted from the finite element simulation based on the measured data. It was found that the dynamic fracture toughness of the delamination crack propagating at a speed up to 1000 m/s approximately equals the static fracture toughness.     

Dynamic fracture of tungsten base heavy alloys

A recently developed short beam experimental technique has been applied to the characterization of the mode I dynamic fracture toughness (KId) of a commercial tungsten base heavy alloy (w/o-90W-7Ni-3Fe). The specimens were taken from a cylindrical swaged alloy bar and tested at a typical loading rate of the order of 10⁶ MPa\sqrtm/s. Three different crack orientations (one longitudinal and two radial) were investigated. The KIdvalues obtained for the three crack orientations are compared with the corresponding values obtained under quasi-static loading conditions (KIc). Our results show that the dynamic fracture of heavy alloys is both anisotropic and rate sensitive. For specimens containing radial cracks (LR, RR), the dynamic fracture toughness is higherthat its static counterpart. By contrast, for longitudinal cracks (RL), the dynamic fracture toughness is lowerthan the static one. Also, for radial cracks, both the (average) static and the dynamic fracture toughness are higher than in the longitudinal orientation. These new results about the anisotropy of the dynamic fracture toughness of the heavy alloys are reported and correlated with metallographic and fractographic examinations.     

A model for the dynamic fracture toughness of ductile structural steel

We assume in this paper that the dynamic fracture toughness K_Id of ductile structural steels is dependent on void nucleation and void growth. The void nucleation-induced dynamic fracture toughness K_Id·n and the void growth-induced dynamic fracture toughness K_Id·g were obtained by modifying the void nucleation-induced and void growth-induced static fracture toughness models, respectively, considering the effect of strain rate and local temperature. By the relationship between the void nucleation-induced dynamic fracture toughness K_Id·n and the void growth-induced dynamic fracture toughness K_Id·g((K_Id)²=(K_Id·n)²+(K_Id·g)²) dynamic fracture toughness K_Id could be quantitatively evaluated. With this model the dynamic fracture toughness of two structural steels (X65 and SA440) was assessed, and the causes for the differences between the static and dynamic fracture toughness were also discussed.     

MTS万能材料试验机在石油管材止裂韧性测试中的应用

建立起以MTS810.15万能材料试验机为主体的材料止裂韧性试验装置,对石油天然气输送管材进行了平面应变止裂韧性(K_(la))测试.结果表明可以运用MTS万能材料试验机进行材料止裂韧性试验,并对材料的止裂韧性进行了分析探讨.     

GCr15钢接触疲劳寿命与断裂韧度关系的研究

对五种不同硫含量(0.009—0.092wt％)的GCr15钢进行了接触疲劳试验并测试了其断裂韧度K_(IC)值。试验数据进行了较为严格的统计处理,研究了接触疲劳寿命与断裂韧度K_(IC)的相关性。统计分析结果表明:GCr15钢的额定寿命L10与K_(IC)相关性不显著,但中值寿命L50与K_(IC)之间具有显著的相关性。因此,断裂韧度K_(IC)有可能作为中值寿命L50的一种度量。     

预加载下岩石的动态力学性能研究

动态和静态载荷共同作用下的岩石力学特性是深部地下岩石工程的关键问题。设计了用于测试静态预加载下岩石动态力学性能的分离式霍普金森压杆系统,并详细介绍了具有预加载装置的分离式霍普金森压杆系统的原理、数据分析和应力波的传播过程。通过具有预加载装置的分离式霍普金森压杆系统研究了岩石在不同预拉伸应力下的拉伸强度。结果表明:动态拉伸强度和总拉伸强度随着加载率的增加而增加,同时,在相同加载率下,动态拉伸强度随着预拉伸载荷的增加而减小,而总拉伸应力与预拉伸载荷的大小无关。此外,对不同预加载条件下岩石的动态断裂韧度也进行了研究,实验结果说明岩石的动态断裂韧度和总断裂韧度随着加载率的增加而增加。在相同加载率下,动态断裂韧度随着预加载荷的增加而减小,而总断裂韧度随着加载率的增加而增加。     

Experimental and numerical study on dynamic fracture behaviour of AISI 1045 steel for compressor crankshaft

Dynamic fracture behaviour of AISI 1045 steel for compressor crankshaft was studied by experimental and numerical methods. True stress–strain relations of the material under different strain rates were measured, and dynamic constitutive model with consideration to strain‐hardening and strain‐rate hardening was proposed. Dynamic fracture tests loaded by Hopkinson pressure bar were carried out, and fracture toughness was determined using a finite element method with the combination of ABAQUS and Zencrack software. Loading states of the specimen and determination methods of the dynamic fracture toughness were discussed. By comparing the fracture behaviours under quasi‐static and dynamic conditions, it was found that the fracture modes exhibited a transition from ductile to brittle fracture with the increasing loading rate, and the dynamic fracture toughness value was less than the quasi‐static one.     

Effect of pre-strain on fracture toughness of ductile structural steels under static and dynamic loading

The ductile fracture process consists of void nucleation, growth and coalescence. The whole ductile process can be divided into two successive steps: (I) the initial state to void nucleation, followed by (II) void growth up to void coalescence. Based on this suggestion, resistance to ductile fracture could be divided into the resistance to stage I and stage II, and accordingly the whole fracture toughness could be regarded to be due to contributions from stages I and II. The fracture toughness contributed from the two steps is, respectively, denoted as void nucleation-contributed fracture toughness and void growth-contributed fracture toughness. The effect of plastic pre-strain on the fracture toughness of ductile structural steels under static and dynamic loading (4.9 m/s) within the ductile fracture range was evaluated by summing contributions due to void nucleation-contributed and void growth-contributed fracture toughness. The effect of strain rate on fracture toughness was also investigated by the same means. The results show that both plastic pre-strain and high-speed loading decrease the void nucleation-contributed fracture toughness while their effects on the void growth-contributed fracture toughness depend on the variations in strength and ductility. Moreover, fracture toughness of structural steels generally decreases with increasing strain rate.     

应力与氢对40Cr钢断裂特征的影响

本文利用悬臂梁试验机,测定了40Cr 钢的断裂韧性 K_(1c)和在3.5%NaCl溶液中,充氢达饱和条件下的氢脆临界应力场强度因子 K_(IH),以及在不同的应力场强度因子 K_(Ii)下的裂纹扩展速率 da/dt,并结合 SEM 对断裂形态进行了分析。