A7N01P-T4铝合金激光-MIG复合焊接头微区性能

以高速列车用14 mm A7N01P-T4铝合金为研究对象,对其激光-MIG复合焊接头的焊缝（WM）、热影响区（HAZ）两个微区以及母材（BM）进行微区拉伸、断裂韧度等性能测试,并结合金相、断口扫描等分析该种接头各区及母材的性能差异.结果表明,A7N01P-T4铝合金母材的抗拉强度最高,其次为激光-MIG复合焊接头热影响区,焊缝最差;接头热影响区的断裂韧度J_m（14）值最高,约为119.580 kJ/mm2,其抵抗裂纹扩展的能力是3个区域中最强的;Shapiro-Wilk正态性检验表明,A7N01P-T4铝合金激光-MIG复合焊接头的断裂韧度测试结果具有较高的可靠性.     

高速列车用6061和7N01铝合金焊接接头断裂韧性分析

按照国家标准GB/T 21143-2007《金属材料准静态断裂韧度的统一试验方法》求得高速列车用6061和7N01铝合金焊接接头中焊缝、热影响区和母材3个区域的CTOD值δ_c和J积分值J_c,借助于数理统计的方法对焊接接头的断裂韧性进行了分析,并结合金相组织和断口形貌分析了它们之间关系.结果表明,对数正态分布对小样本断裂韧性数据拟合程度最好;6061和7N01铝合金焊接接头中各区域δ_c值和J_c值热影响区最大,焊缝次之,母材最小;6061和7N01铝合金焊接接头比较,7N01铝合金焊接接头中母材和焊缝的δ_c值和J_c值都优于6061铝合金焊接接头的相同区域;热影响区的δ_c值6061铝合金优于7N01铝合金;而热影响区的J_c值7N01铝合金优于6061铝合金.     

焊接热循环对A5083P-O和A7N01P-T4铝合金接头组织性能的影响

针对铝合金车体生产中焊接热循环对铝合金接头组织性能的影响,选择A5083P-O、A7N01P-T4两种铝合金材料,在相同的焊接环境、拘束条件下,采用相同的焊接参数,经过不同次数焊接热循环后,对试样进行无损检测、金相组织及硬度分析,结果发现A5083P-O、A7N01P-T4材料具有不同的热裂纹倾向性,为后续生产中多次修补提供理论依据。     

坡口型式对厚板A7N01铝合金激光-MIG复合焊接接头组织性能的影响

针对15 mm厚A7N01P-T4铝合金板的激光-MIG复合焊接进行坡口设计,通过对接头宏观成型、无损探伤、金相组织观察和力学性能试验来选择最合适的坡口型式。结果表明:激光-MIG复合焊接对试验采用的三种坡口型式适应性良好,可获得宏观成型良好、力学性能稳定的焊接接头。当采用单边20°坡口型式时,焊接速度快、线能量低、接头抗拉强度较其他两种坡口型式稍高。因此,建议激光-MIG复合焊接15 mm厚A7N01P-T4铝合金板时采用单边20°的坡口型式。     

激光热源偏移对6mm A7N01铝合金激光-MIG复合焊焊接头的质量影响

针对铝合金激光-MIG复合焊接过程中的热源偏移问题,采用激光-MIG复合焊对6 mm厚A7N01P-T4铝合金进行焊接,给定热源对中偏移,并分析无对中偏移及有对中量偏移的焊接接头宏观成形、微观组织、力学性能,以此研究热源对中偏移对6 mm厚A7N01铝合金激光-MIG复合焊接接头的影响。研究结果表明,有热源对中偏移的试板接头内部存在少量的气孔缺陷,与无对中偏移试板相比,拉伸性能下降21 MPa。     

A7N01铝合金焊接接头的补焊性能分析

以高速列车用A7N01铝合金原始焊接接头和一次补焊接头为研究对象,通过残余应力测试、拉伸试验、硬度试验、金相分析以及断裂韧度测试等手段对补焊前后焊接接头力学性能进行了研究,基于断裂力学理论对补焊前后焊接接头进行了力学性能测试和显微组织分析,依据试验结果对补焊前后构件临界失稳断裂长度进行计算,由金相分析结果假定补焊前后初始裂纹长度,利用Paris公式对含有初始缺陷的补焊前后焊接接头进行疲劳剩余寿命计算,计算结果说明尽管补焊工艺一定程度造成了材料性能损失,在存在裂纹的情况下依然是一种有效的提高构件承载能力的方法.     

A7N01铝合金激光-MIG复合焊接工况适应性研究

针对高速列车用6 mm厚A7N01P-T4铝合金,选择不同的焊接速度、坡口间隙、热源间距、错边量等进行激光-MIG复合焊接,并分析焊接接头的宏观成型、显微组织及力学性能,以此研究激光-MIG复合焊接的工况适应性。研究结果表明:激光-MIG复合焊接6 mm厚A7N01P-T4铝合金板,焊接速度在0.9~1.1 m/min时可以获得成型良好、性能稳定的接头;热源间距在1~4 mm时可获得成型良好、性能稳定的接头;错边量在1.0 mm以下时的焊接接头成型良好、力学性能正常;坡口间隙在1.0~1.2 mm时获得的接头成型最好,性能也最佳。     

背面成形对A7NO1铝合金激光-MIG复合焊接头组织性能的影响

针对高速列车用6 mm厚A7N01P-T4铝合金,进行强制成形和背部加永久垫板两种接头形式的激光-MIG复合焊接试验,并对比分析焊接接头的宏观成形、显微组织、力学性能,以此研究激光-MIG复合焊对两种接头型式的适应性。实验结果表明,两种接头型式均可获得外观成形良好、显微组织正常的焊缝;而力学性能方面,当背部加永久垫板时的接头抗拉强度较强制成型时的接头提高11 MPa,激光-MIG复合焊接高速列车用6 mm厚A7N01P-T4铝合金板时采用背部加永久垫板的接头形能取得较好的性能。     

轨道车辆减振器座焊接工艺

轨道车辆减震器座由铝合金板材拼接而成,其结构焊接结构复杂,焊缝较多,且焊后残余应力较多。针对其MIG焊接工艺,通过试验测试和数值模拟的方法,得出焊接数值模拟方法的可靠性,并验证了目前现场使用的焊接工艺的合理性。进一步提出合理的焊接工艺。减振器座焊后残余应力测试采用盲孔法测试技术测量。减震器座数值模拟采用三维热弹塑性有限元法模拟焊接方法,焊接数值模拟软件为SYSWELD v2012,建立了轨道车辆减震器几何模型、热源模型与材料A7N01P-T4的力学模型。     

A7N01P铝合金T型接头焊接数值模拟

针对A7N01P铝合金T型接头的焊接,开展基准性研究,其目的是为复杂焊接结构数值模拟提供可靠的数值模拟方法。本研究建立A7N01P铝合金焊接热源模型和材料软化模型,采用三维热弹塑性有限元法模拟焊接过程,比较数值模拟结果与焊接试验测试结果,验证焊接数值模拟方法的可靠性。结果表明,焊接数值模拟的温度场和残余应力与实测值非常吻合,验证了数值模拟模型的准确性。     

Determination of the toughness of in-service steam turbine disks using small punch testing

Knowledge of the material toughness is crucial in assessing the integrity of heavy section steel components. Conventional tests to determine the toughness involve extraction of large blocks of materials and therefore are not practical on in-service components. On the other hand, conservative assumptions regarding toughness without regard to actual data can lead to expensive and premature replacement of the components. Previous EPRI studies have demonstrated the use of a relatively nondestructive technique termed the “small punch test” to estimate the fracture appearance transition temperature (FATT) and fracture toughness (K _Ic ) of high-temperature turbine rotor steels and nuclear reactor pressure vessel steels. This paper summarizes the results of research into the feasibility of extending the small punch test to characterize the toughness of the 3 to 3.5% NiCrMoV (3–3.5NiCrMoV) low alloy steel used for fossil and nuclear power plant low-pressure (LP) steam turbine disks. Results of the present study show that the small punch transition temperature, T _sp , is linearly correlated with FATT, so that measurement of T _sp permits estimation of the standard Charpy FATT through empirical use of the correlation. The statistical confidence prediction uncertainty bands for the correlation were found to be narrow enough to make the small punch- based FATT estimation practical for this alloy. Additionally, independent K _Ic measurements made by PowerGen, UK, on some of the same test materials were in excellent agreement with measurements made here, indicating that the small punch K _Ic measurement can be reproducible across laboratories. Limited testing for fracture initiation toughness showed, as has been demonstrated for other materials, that the small punch test-based initiation fracture toughness (K _Ic ) determination was within ±25% of the ASTM standard measurement of K _Ic , suggesting that the test method can be used for direct determination of fracture initiation toughness.     

Fracture toughness properties of high-strength martensitic steel within a wide hardness range

Fracture toughness tests were carried out on six grades of high-strength martensitic steel within the hardness range from 270 to 475 HB. Four types of tests were performed: (a) Charpy V-notch (CVN) impact over the temperature range −120 to 60 °C, (b) plane strain fracture toughness, K _IC , near the onset of crack growth, (c) fracture toughness, J _IC , near the initiation of slow crack growth, and (d) fracture toughness, J _iC , and crack tip opening displacement (CTOD _iC ) at the onset of slow crack growth using direct current potential drop (DCPD) technique. Further, true plane strain fracture toughness, K _o , at the onset of crack initiation was determined. Fracture toughness behavior including the measured and determined values of CVN, K _IC , K _o , J _IC , K _iC , and CTOD _iC have been interrelated over the entire hardness range using the various analytical and empirical correlations reported in the literature. The results indicate that the steel acquires the optimum fracture toughness properties at a hardness of 305 HB, corresponding to a tempering temperature of 630 °C. Further, the steel exhibits a slight 300 °C temper embrittlement phenomenon.     

Failure modes and materials performance of railway wheels

In this study, the failure modes of cartwheel and mechanical properties of materials have been analyzed. The results show that rim cracking is always initiated from stringer-type alumina cluster and driven by a combination effect of mechanical and thermal load. The strength, toughness, and ductility are mainly determined by the carbon content of wheel steels. The fatigue crack growth resistance is insensitive to composition and microstructure, while the fatigue crack initiation life increases with the decrease of austenite grain size and pearlite colony size. The dynamic fracture toughness, K _ID , is obviously lower than static fracture toughness, K _IC , and has the same trend as K _IC . The ratio of K _ID /σ _YD is the most reasonable parameter to evaluate the fracture resistance of wheel steels with different composition and yield strength. Decreasing carbon content is beneficial to the performance of cartwheel.     

An investigation on quench cracking behavior of superalloy udimet 720LI using a fracture mechanics approach

Quench cracking can be a serious problem in the heat treatment of high strength superalloys. A new fracture mechanics approach, quench cracking toughness (K _Q ), was introduced to evaluate the on-cooling quench cracking resistance of superalloy Udimet 720LI. A fully automatic computer controlled data acquisition and processing system was set up to track the on-cooling quenching process and to simulate the quench cracking. The influences of grain size, cooling rate, solution temperature, and alloy processing routes on quench cracking resistance were investigated. Research results indicate that quench cracking revealed a typical brittle and intergranular failure at high temperatures, which causes a lower quench cracking toughness in comparison to fracture toughness at room temperature. Fine grain structures show the higher quench cracking resistance and lower failure temperatures than intermediate grain structures at the same cooling rates. Moreover, higher cooling rate results in lower cracking toughness under the same grain size structures. In comparison of processing routes, powder metallurgy (PM) alloys show higher cracking resistance than cast and wrought (CW) alloys for fine grain structures at the same cooling rates. However, for intermediate grain structure, there is no obvious difference of K _Q between the two processing routes in this study.     

Designing highly toughened hybrid composites through nature-inspired hierarchical complexity

The notion of replicating the unique fracture resistance of natural composites in synthetic materials has generated much interest but has yielded few real technological advances. Here we demonstrate how using ice-templated structures, the concept of hierarchical design can be applied to conventional compounds such as alumina and poly(methyl methacrylate) (PMMA) to make bulk hybrid materials that display exceptional toughness that can be nearly 300 times higher (in energy terms) than either of their constituents. These toughnesses far surpass what can be expected from a simple “rule of mixtures”; for a ～80% Al₂O₃–PMMA material, we achieve a K_Jc fracture toughness above 30 MPa m^1/2 at a tensile strength of ～200 MPa. Indeed, in terms of specific strength and toughness, these properties for alumina-based ceramics are at best comparable to those of metallic aluminum alloys. The approach is flexible and can be readily translated to multiple material combinations.     

Welding aluminium alloys using low arc energy MIG method in terms of reducing pollutant emissions

Abstract

A comparison between the Charpy-V (CV) test, widely used in steel characterisation, and the dynamic fracture toughness K_1d found on precracked Charpy testpieces, is carried out.

The experimental procedure, not yet standardised, used to determine the dynamic fracture toughness K_1d (instrumented precracked charpy test or IPC test) is first described.

The experimental procedure, not yet standardised, used to determine the dynamic fracture toughness K_1d (instrumented precracked charpy test or IPC test) is first described.

The conceptual differences between dynamic fracture toughness K_1d and CV impact strength, the limits of CV testing in evaluating the toughness of steels, and finally the advantages of adopting the IPC test and its possible applications in the field of welding are then successively discussed.     

Effect of notch-root radius on the fracture toughness of composite Si3N4 ceramics

In-situ silicon nitride and a whisker-reinforced silicon nitride-silicon nitride composite, densified via gas pressure sintering and hot pressing, respectively, were evaluated using the single-edge V-notched beam (SEVNB) fracture toughness technique. The mean value ofK _IC for each material was 5.7 and 7.9 MPa·m^1/2, respectively, and the toughness was influenced by the presence of the elongated Si₃N₄ grains in the microstructure. The notch radius was observed to have the same effect as a sharp crack when notch-root radius was smaller than 10 μm, which was considered to be a realK _IC for these materials.     

An evaluation of grinding force by the fracture toughness of carbon steel

Grinding force, which is a representative factor of the grindability of a workpiece, is discussed in this study. The metallurgical structures of different carbon steels were classified into two groups according to the magnitude of their grinding force. For each group, the fracture toughness (J_c), was measured. The method used for this measurement was to mount a strain gauge on the hammer of a Charpy impact test machine. The strain at impact fracture was measured and the fracture toughness was calculated, with the results shown on a load-displacement diagram.A comparison of the fracture toughness (J_c) of each material and its grinding force was done. It was found that the fracture toughness (J_c) can be used in estimating the grinding force.     

Tensile and fracture toughness properties of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The goal of this work was to evaluate the effects of particle size, particle volume fraction, and matrix strength on the monotonic fracture properties of two different Al alloys, namely T1-Al2124 and T1-Al6061, reinforced with silicon carbide particles (SiC_p). From the tensile tests, an increase in particle volume fraction and/or matrix strength increased strength and decreased ductility. On the other hand, an increase in particle size reduced strength and increased the composite ductility. In fracture toughness tests, an increase in particle volume fraction reduced the toughness of the composites. An increase in matrix strength reduced both K _crit and δ_crit values. However, in terms of K _Q (5%) values, the Al6061 composite showed a value similar to the corresponding Al2124 composite. This was mainly attributed to premature yielding caused by the high ductility/low strength of the Al6061 matrix and the testpiece dimensions. The effect of particle size on the fracture toughness depends on the type of matrix and toughness parameter used. In general, an increase in particle size decreased the K _Q (5%) value, but simultaneously increased the amount of plastic strain that the matrix is capable of accommodating, increasing both δ_crit and K _crit values.     

Cross-sectional nanoindentation: a new technique for thin film interfacial adhesion characterization

Interfacial adhesion is becoming a critical material property for improving the reliability of multilayer thin film structures used in microelectronics. Cross-sectional nanoindentation (CSN) is a new mechanical test especially designed for measuring the fracture toughness of thin film interfaces. Interfacial fracture is achieved by nanoindentation in the structure cross-section. A model based on the elastic plate theory has been developed to calculate numerically the interfacial critical energy release rate (G_ci) for ceramic–ceramic systems from CSN test results. The model inputs are the thin film elastic properties, thin film thickness, interfacial crack area and maximum thin film deflection during the test. Closed form analytical solutions, obtained for two limiting cases, are consistent with the numerical approach. This technique has been successfully applied to silicon nitride–silicon oxide thin films, commonly used as electrical isolators in microelectronic devices.