夏比V型缺口冲击吸收能量测试失准原因的探讨

针对夏比V型缺口冲击吸收能量的实际测量值明显偏高的情况,调查了夏比冲击试验测试值失准的原因,具体分析了加工方法、加工设备和测量方法对夏比V型缺口冲击试样尺寸及测量精度的影响,以及如何避免冲击吸收能量测试值失准的措施及建议。     

V型缺口冲击试样尺寸公差因素的有限元分析

对照GB/T 229-2007和ASTM E23-2012c(2014)对V型缺口冲击试样的加工要求,使用有限元模拟计算方法,分析了试样尺寸公差对试样缺口处应力的影响,并利用缺口处的应力评估了尺寸公差对缺口敏感性的影响权重。结果表明:缺口底部高度和缺口角度对试样缺口敏感性的影响权重最大;试样宽度和高度的影响次之,试样长度的影响最小;相比较,ASTM E23-2012c(2014)对V型缺口冲击试样加工尺寸公差的要求比GB/T 229-2007更为合理。     

金属夏比试样V型缺口尺寸的简易测量法

新国标GB/T229—1994《金属夏比缺口冲击试验方法》对标准夏比V型缺口试样的整角度、半角度、根部半径的偏差做了明确的规定.由于缺口尺寸的超差,就会严重地影响试验结果,只有保证缺口尺寸在正、负偏差之中,才能得到正确的冲击吸收功.为了准确、快速地测量缺口尺寸,可以利用一只废手工锯条,剪成一个长的,一个短的.对长的要制成正偏差样板,为47°角,根部半径R0.275mm.对短的要制成负偏差样板,为43°角,根部半径RO.225mm.制做样板时,如图1.首先用细砂轮分别把这两只锯条磨成一个略大于47°角,另一个略大于43°角.然后,用精磨油石一边磨,一边标定角度和半径.最后,用细金相砂纸铺垫玻璃再磨,提高了光洁度,保证了样板实际尺寸的精确.对于这两只样板要选用精度较高的设备进行标定.试作整角度与根部半径的测量:用正偏差样板,插入试样缺口根部,存在间隙认为尺寸大于正偏差值,就为不合格.无间隙认为在正偏差中,试样为合格.不能插入到根部,缺口角度为小于正偏差值,但是,不可超出负偏差极限,认为合格.用负偏差样板,插入试样缺口根部,无间隙认为     

GB/T 229-2007关于夏比V型缺口冲击试样几何参数的规定及其加工方法

现行的冲击试验标准GB/T 229-2007,对夏比V型缺口冲击试样几何参数的规定较1994年颁发的旧标准GB/T 229—1994变化较大,通过将新标准、旧标准以及美标ASTM E23—02a对冲击试样几何参数的规定进行对比分析,认为GB/T 229-2007相比GB/T 229-1994对夏比V型缺口冲击试样几何参数的放宽和规定更加科学、合理。另外还对目前夏比V型缺口冲击试样的几种加工方法进行了比较分析,认为组合机床是冲击试样加工设备的发展方向。     

金属材料试样制备与力学性能试验结果的相关性第三讲试验标准对力学性能试验试样机加工的具体要求(续)

4．2国家标准对冲击试样机加工的要求 GB／T229—1994标准规定了V型缺口和U型缺口两大类共计三种标准试样,如图27～29所示,其中U型缺口标准夏比冲击试样又分为两种。     

金属断裂韧性与缺口试样冲击功间普遍关系与应用

从冲击功着手，推导出在常温相同断裂机制条件下，缺口试样冲击功（ＣＶＮ）和断裂韧性ＫＩＣ间普遍关系。并用回归法求出了４０ＭｎＶＴｉ微合金钢Ｋ＾２ＩＣ与夏比Ｖ型缺口试样冲击功（ＣＶＮ）间线性回归方程。     

标准冲击试样在仪器化摆锤冲击试验机检定中的应用

通过分析仪器化摆锤冲击试验方法的测试结果,研究标准冲击试样在仪器化摆锤冲击试验机(以下简称试验机)间接检定中的适用性.对比冲击过程的特征曲线和标准试样的吸收能量,结果表明利用夏比V型缺口标准冲击试样对仪器化摆锤冲击试验机进行间接检定,更加科学合理.     

金属夏比缺口(V型)室温冲击试验检测结果不确定度的评定

介绍了测量不确定度在金属夏比（V型缺口）室温冲击试验中的应用，并对影响冲击试验结果的测量不确定度做了详细评定，从试样的形状和尺寸、缺口底部的光洁度、冲击试验机、试验温度、检查试样尺寸量具的最小分度值五方面分析了不确定度的来源，对各分量进行了计算、合成并作出评定。     

HQ785C钢示波冲击特性的缺口效应研究

采用示波冲击试验方法，研究了ＨＱ７８５Ｃ钢的夏比Ｖ型缺口、线切割缺口和预疲劳裂纹３种类型试样在冲击断裂过程中各部分能量与温度的关系。分析了各部分能量随温度变化的规律。试验结果表明，预疲劳裂纹试样的脆性转变温度比线切割缺口试样和夏比Ｖ型缺口试样分别提高约２０℃和４０℃。     

冲击缺口类型对34CrNi1Mo钢韧脆转变温度的影响

对34CrNi1Mo钢分别进行V形和U形两种缺口类型的冲击试验,并绘制出剪切断面率与试验温度的曲线。通过曲线及韧脆转变温度的对比,分析缺口类型对34CrNi1Mo钢韧脆转变温度的影响。结果表明:不同缺口类型对34CrNi1Mo钢的韧脆转变温度有较大影响,U形缺口试样测得的韧脆转变温度低于V形缺口试样测得的韧脆转变温度。     

试样厚度对夏比冲击试验结果的影响

通过不同温度下的夏比摆锤冲击试验对非标准小尺寸V型缺口冲击试样的冲击吸收能量和侧膨胀值进行了分析,并结合力-位移曲线,研究了试样厚度对冲击试验结果的影响。结果表明:当试验温度高于韧脆转变温度时,冲击吸收能量与试样的横截面积有关,因此与厚度呈线性关系;而低于韧脆转变温度时,冲击吸收能量与试样厚度之间没有明显关系;试样的侧膨胀值、剪切断面率与厚度之间没有直接联系。随着试样厚度的减小,不稳定裂纹扩展起始力越来越小,从而导致冲击吸收能量减小。厚度越大试样吸收的能量越多,冲击过程中所受到的最大力也越大。     

Impact toughness of high strength low alloy TMT reinforcement ribbed bar

Charpy V-notch impact toughness of 600 MPa yield stress TMT rebars alloyed with copper, phosphorus, chromium and molybdenum has been evaluated. Subsize Charpy specimens were machined from the rebar keeping the tempered martensite rim intact. The copper-phosphorus rebar showed toughness of 35 J at room temperature. The toughness of copper-molybdenum and copper-chromium rebars was 52 J. The lower toughness of phosphorus steel is attributed to solid solution strengthening and segregation of phosphorus to grain boundaries. Due to superior corrosion resistance, copper-phosphorus TMT rebar is a candidate material in the construction sector.     

Statistical scatter in the fracture toughness and Charpy impact energy of pearlitic steel

The effect of microstructure on the fracture characteristics of high carbon hypo eutectoid steel was studied under conditions of quasistatic and dynamic loading. Experimentally determined sets of fracture toughness and Charpy impact energy values were statistically treated. A relationship was found between fracture toughness and Charpy impact energy. In the very brittle domain, the fracture toughness increases slightly with increasing Charpy impact energy. In the domain where the fracture toughness is higher, the rise in fracture toughness with increasing Charpy impact energy is more pronounced. Detailed SEM examination of fractured compact tension (CT) and Charpy V-notch (CVN) specimens showed that the fracture at ambient temperature occurred almost exclusively by cleavage. There were no visible differences in the morphology of cleavage facets on the fracture surfaces of Charpy and CT specimens. Mechanisms of cleavage initiation were revealed by the fractographical investigation of fracture surfaces. Whereas the fracture surfaces of broken CT specimens exhibit a number of cleavage origins, the fracture surfaces of CVN specimens usually show only one.     

Performance Verification of Impact Machines for Testing Plastics

Valid comparison of impact test energies reported by various organizations and over time depends on consistent performance of impact test machines. This paper investigates the influence of various specimen and test parameters on impact energies in the 1 J to 2 J range for both Charpy V-notch and Izod procedures, leading toward the identification of a suitable material for use in a program to verify machine performance. We investigated the influences on the absorbed energy of machine design, test material, specimen cross sectional area, and machine energy range. For comparison to published round robin data on common plastics, this study used some common metallic alloys, including those used in the international verification program for metals impact machines and in informal calibration programs of tensile machines. The alloys that were evaluated include AISI type 4340 steel, and five aluminum alloys: 2014-T6, 2024-T351, 2219-T87, 6061-T6, and 7075-T6. We found that certain metallic alloys have coefficients of variation comparable to those of the best plastics that are reported in the literature. Also, we found that the differences in absorbed energy between two designs of machines are smaller than the differences that can be attributed to the specimens alone.     

金属夏比V型缺口标准试样的研制

介绍了金属夏比V型缺口标准试样的研制原理,采用40CrNiMo制做了低能量和中能量两个能量级的标准试样,并在国家基准冲击试验机上进行试验。结果表明,低能量标准试样的平均冲击值为24.84 J,标准偏差为1.4 J,半年稳定性为0.7%;中能级标准块的平均冲击值为97.51 J,相对标准偏差为3.0%,半年稳定性为0.8%,符合国家标准GB/T 18658-2002要求,实现了冲击能基准量值传递的目标。同时分析了冲击试样加工工艺及其形貌、相结构对冲击能量值的影响。     

借助准标样测算夏比冲击试验测量不确定度的方法

为解决在测定材料冲击吸收功出现用户验收结果与出厂检验结果不一致的问题,提出了用准标样测算冲击试验测量不确定度的方法。这种方法可作为双方在进行冲击值比对分析时都能接受的评定方法。     

Comparison of tensile and impact behavior of carbon steel in H2S environments

The present research reports the effect of hydrogen sulfide pressure on the tensile and impact behavior of carbon steel. Hydrogen content measurement was conducted due to the relationship between hydrogen and mechanical behavior. A remarkable increase in the relative tensile strength and plasticity loss was observed as hydrogen sulfide pressure increased. However, the Charpy absorbed energy showed no obvious change with increase of H₂S pressure from 0.1 MPa to 1.6 MPa, even though a significant decrease compared to that of as-received steel. Combined with the results of hydrogen content measurement, it was found that hydrogen has a profound effect on the tensile and impact behavior of steel. Fractography of the corroded tensile and impact specimens exhibited mixed ductile–brittle rupture. In addition, the brittle zone on the fracture surface increased for corroded tensile specimens and showed nearly similar area fraction for corroded impact specimens as H₂S pressure increased. A probable mechanism is proposed to interpret the difference in the tensile and impact results.     

Evaluation of fracture appearance transition temperature to forged 3Cr–1Mo–0.25V steel using ultrasonic characteristics

This paper reports that the ultrasonic methods can be used to accurately characterize forged reactor vessels. The Charpy V-notch impact tests were conducted on the respective specimens with three different types of heat history. Various test results including fracture appearance transition temperature (FATT) were obtained. A pulse-echo method with longitudinal waves was used to measure attenuation and velocity of ultrasonic wave. The velocity was measured repeatedly nine times on each specimen. The attenuation coefficient of the ultrasonic wave changed with heat treatment temperature and conditions (as-quenched, tempered, PWHT). The fracture appearance transition temperature can be predicted using the ultrasonic characteristics.