拉伸速率控制模式及拉伸速率对冷轧薄板强度测试结果的影响

按照GB/T 228.1—2010中推荐的不同拉伸速率控制模式及拉伸速率对冷轧镀锌钢板进行了拉伸对比试验,分析了应变速率、横梁位移速率及应力速率对冷轧薄板规定非比例延伸强度R_p0.2、下屈服强度R以及抗拉强度R_tn测试结果的影响。结果表明:采用应变速率进行控制得到的拉伸试验数据相对其他两种速率控制模式更为稳定,可以最大限度地降低拉伸测试结果的不确定度;采用0.000 25 s^-1的应变速率控制模式所得试验结果的稳定性与采用40～50 MPa·s^-1的应力速率控制模式所得结果较为接近;在不同拉伸速率控制模式下,提高应变、横梁位移和应力速率均会使屈服强度R_p0.2和R_el增加,而抗拉强度R_tn基本上处于稳定状态。     

BOPP料的应力-应变行为

通过对BOPP进口料与国产料应力－应变行为的比较,得到了各种原料的屈服应力（σy),屈服应变（εy）,断裂应变（σb),断裂应变（εb)及模量（E）等随拉伸速率的变化关系。分析结果表明,各种原料在生产中表现出的不同的加工特点是由其不同的应力－应变行为引起的;进口料的应力－应变性能波动较小,可能有助于材料在实际加工过程中的稳定;各种原料的应力－应变性能在拉伸速率为100mm/min时较好,这可能有助于寻找BOPP最佳的加工窗口,通过本研究及其后续工作,可望能对国产PP的加工和应用起一定的指导作用。     

不同控制模式下拉伸试验速率的测试及方法比较

针对GB／T228．1-2010中方法A、方法B、附录F以及横梁控制4种不同拉伸速率控制模式,采用两组薄板在Z100拉伸试验机做不同控制模式的试验速率试验,并对4种方法进行分析比较。结果表明：对于大部分黑色金属材料来说,4种拉伸速率控制方法对力学性能结果的影响不明显,仅对部分应变速率敏感的材料结果才会有差异;实施方法A时虽然平均应变速率恒定,但实际应变速率超过误差限,偏离方法A;实施方法B时,建议在RP,ReH阶段采用与屈服阶段相同的速率控制模式,以避免试验失控。实施附录F时,Rp,ReH阶段参数m与弹性阶段的参数E不能等同,设置速率Ⅵ：不应与弹性阶段相同。     

63Sn-37Pb和Sn-0.7Cu钎料的力学性能

对63Sn-37Pb和Sn-0.7Cu两种钎料进行了单轴拉伸试验、纯扭试验和纯扭疲劳试验.结果表明,钎料拉伸和纯扭时的应力应变关系有很强的应变速率相关性.弹性模量和剪切模量受应变速率的影响很小.钎料的屈服强度、剪切屈服强度、抗拉强度和抗剪强度也受应变速率的影响.钎料是剪切型破坏材料,并且发生循环软化.     

三种控制方式在GB/T228.1-2010中的正确应用

为了满足GB/T 228.1-2010中方法 A对拉伸速率的要求,阐述了应变控制、应力控制和位移控制三种控制方式对金属材料拉伸性能的影响,提出了一种考虑了系统柔度的准应变速率控制方法,即用准应变全程位移自动控制间接实现对试样的应变速率控制。采用准应变速率控制方法时,无论测试何种金属材料、何种尺寸试样,试验人员仅需输入试样尺寸和估计的弹性模量,由程序自动计算出系统柔度和各阶段拉伸速率,即可对整个试验过程进行自动控制,使不同试验机得出的试验结果真正具有可比性。     

超高强铁素体-马氏体双相钢在动态拉伸变形条件下组织和性能研究

通过分段淬火连续退火实验,获得两组铁素体晶粒尺寸大致相同、马氏体体积分数不同的双相钢。选取应变速率为10-4s-1进行准静态拉伸实验;选取应变速率为500s-1和2250s-1在分离式霍普金森拉杆技术进行动态拉伸实验。利用动态因子、Feret比率等定量分析方法研究超高强铁素体-马氏体双相钢在动态拉伸变形条件下的组织和性能。结果表明:应变速率效应在双相钢的动态变形行为中主要起强化作用;马氏体体积分数越低的双相钢应变速率敏感性越大;相比抗拉强度而言,超高强冷轧双相钢屈服强度的应变速率敏感性更大。计算在应变速率为2250s-1动态拉伸变形下产生绝热温升分别为98K和89K,并抵消部分应变速率强化作用。     

金属材料拉伸的高应变率增塑现象及分析

用动态拉伸法研究了三种金属材料塑性随应变率的变化而变化的情况,应变率范围为１０＾－４￣１０＾３ｓ＾－１研究发现,随着应变率的升高,三种金属的塑性都有不同程度的提高。其中３０ＣｒＭｎＳｉＮｉ２Ａ淬火态在０．５ｍｍ·ｍｉｎ＾－１加载速率时延伸率仅为７０％,而在４０ｍ·ｓ＾－１时为１４．５％,提高了一倍多,表现出典型的高应变率增塑现象,微观实验及分析表明,高应变率增塑现象的机理和高应变率导致的温度升高,     

铝合金应力腐蚀的电化学研究

应用电化学测试法、恒载荷拉伸法和慢应变速率拉伸法研究了硬铝合金LY12 3.5 %NaCl溶液应力腐蚀体系的电化学特性。结果表明应变速率比应力对电化学特性的影响更大。应变速率为 1.13× 10 - 5/s时 ,应力腐蚀较为敏感 ;形变强化阶段力学、化学效应最为明显 ;LY12的应力腐蚀开裂是阳极溶解和氢脆共同作用的结果     

钛合金的银脆,镉脆敏感性及其控制

利用慢应变速率拉伸技术（ＳＳＲＴ），并结合恒载实验，较全面地研究了Ｔｉ－６Ａｌ－４Ｖ合金的银脆行为、固态与液态镉脆行为，确定了应变速率、接触条件、热处理制度、试样取向、温度等因素对Ｔｉ－６Ａｌ－４Ｖ合金银脆与镉脆敏感性的影响，探讨了Ｎｉ阻挡层对控制Ｔｉ－６Ａｌ－４Ｖ合金和ＴＣ１１合金银脆开裂的作用。     

GB/T228.1-2010中的拉伸试验速率及其控制

阐述了在拉伸试验中,试验速率对材料屈服性能表现出规律性的影响。我国历次拉伸试验标准(GB/T 228)有关试验速率的理论规定都是以应变速率为标准,但在实际操作中又都是以等效的应力速率为标准;而在新标准GB/T 228.1-2010中,则从理论规定到实际操作均实现了以应变速率为标准的方法。另外还讨论了拉伸试验速率的控制方法,以及试验速率控制与试验设备的关系。     

Tensile mechanical behavior of T300 and M40J fiber bundles at different strain rate

Tensile mechanical behavior of T300 fiber bundles and M40J fiber bundles have been studied in the strain rate range from 0.001 1/s to 1300 1/s and complete stress strain curves were obtained. Results show that both ultimate strength and failure strain of two materials are strain rate insensitive, and T300 fiber and M40J fiber can be regarded as strain rate insensitive materials. On basis of the fiber bundles model and the statistic theory of fiber strength, single Weibull distribution model and bimodal Weibull distribution model have been developed to describe mechanical behavior of fiber bundles. And a method for determine the statistic parameters of fibers by tensile tests of fiber bundles is established, too. The simulated stress strain curves from the model are in good agreement with the test data. Simulated results show that the strength of T300 fiber can be described by single Weibull distribution function, and the strength of M40J fiber should be described by bimodal Weibull distribution function.     

Tensile behavior of carbon fiber bundles at different strain rates

Quasi-static and high strain rate tensile tests have been performed on T700 carbon fiber bundles and complete stress-strain curves at the strain rate range of 0.001 s^− 1 to 1300 s^− 1 were obtained. Results show that strain rate has negligible effect on both ultimate strength and failure strain, and T700 carbon fiber can be regarded as strain rate insensitive materials. On the basis of the fiber bundles model and the statistic theory of fiber strength, a damage constitutive model based on Weibull distribution function has been developed to describe tensile behavior of T700 fiber bundles. And the method to determine the statistic parameters of fibers by tensile tests of fiber bundles is established, too.     

Experimental Study on Tensile Behavior of Carbon Fiber and Carbon Fiber Reinforced Aluminum at Different Strain Rate

In this study, dynamic and quasi-static tensile behaviors of carbon fiber and unidirectional carbon fiber reinforced aluminum composite have been investigated. The complete stress–strain curves of fiber bundles and the composite at different strain rates were obtained. The experimental results show that carbon fiber is a strain rate insensitive material, but the tensile strength and critical strain of the C_f/Al composite increased with increasing of strain rate because of the strain rate strengthening effect of aluminum matrix. Based on experimental results, a fiber bundles model has been combined with Weibull strength distribution function to establish a one-dimensional damage constitutive equation for the C_f/Al composite.     

Experimental evaluation of the strength distribution of fibers under high strain rates by bimodal Weibull distribution

This paper proposes a bimodal Weibull distribution model for strain- rate- and temperature-dependent fiber strength. The relationships of the mechanical quantities between fiber and fiber bundles at different strain rates and temperatures under tensile impact are established. A method for determining mechanical parameters of fibers by tensile impact tests of fiber bundles is established. Experiments on E-glass bundles have been performed at six strain rates (90, 300, 800, 1100, 1300 and 1700 s⁻¹) at three different temperatures (−70, 14, 80°C). According to the statistical analysis and models, the mechanical parameters for the fiber and their relationships with strain rate and temperature are obtained from the tensile impact experimental results. The emulated stress/strain curves from the model are in good agreement with the test data. The theoretical model and test results show that the shape parameters, β^d₁ and β^d₂, are not only strain rate independent but also temperature independent. The scale parameters σ^d₀₁ and σ^d₀₂, which change with strain rate and temperature, are not constant.     

Statistical Tensile Strength for High Strain Rate of Aramid and UHMWPE Fibers

Technora,madefromaramidfibersandsome whatsimilartothecommonlyknowKevlar,and Ultrahighlyorientedhighmolecularweightpolyeth ylene UHMWPEfibersarealloftenusedinflexible armourapplicationsandhencesubjectedtohighrates ofloading.Theutilizationoftheirreinforcedcom positesarmourincertainballisticapplicationsisin creasinglypreferredoverconventionalrigidmetalar moursystemsbecauseofitssuperiorstrength to weightratioandflexibility.Todate,thedesignand developmentofsuchfabricarmoursystemshave largelybeen…     

Compression test of a single carbon fiber in a scanning electron microscope and its evaluation via finite element analysis

A longitudinal compression test for a single polyacrylonitrile-based carbon fiber (T300) was performed using a scanning electron microscope. The compressive stress/strain behavior was initially linear, but subsequently became nonlinear. The longitudinal tangent modulus decreased with increasing compressive strain. A cyclic compression test revealed that the T300 carbon fiber deformed elastically up to ~90% compressive strength. The variability in the compressive strength was evaluated using Weibull analysis. The representative compressive strength of the T300 carbon fiber was nearly the same as the tensile strength. The compressive strength of the T300 carbon fiber was almost same as that of the high-tensile strength T800S carbon fiber. Finite element analysis was performed to investigate the validity of the test method. The results showed that the longitudinal compressive stress on the carbon fiber varied during longitudinal compressive loading. The maximum longitudinal compressive stress in the carbon fiber was slightly higher than the average compressive strength applied at the end. However, the variability in the measured compressive strength was much higher than that in the longitudinal compressive stress on the carbon fiber, which does not affect the former.     

Experimental and theoretical study on the strain rate and temperature dependence of mechanical behaviour of Kevlar fibre

The tensile impact experiments on Kevlar 49 fibre bundles were carried out at strain rates 140, 440, 1350 s⁻¹ and at temperatures −60, −20, 15, 50 and 90°C. It was found that the tensile mechanical properties of Kevlar 49 fibre bundles depend both upon the strain rate and the temperature. A bimodal Weibull distribution statistical model of the strain rate and temperature dependence of fibres, and a test method of determining mechanical properties and Weibull parameters of fibres from the fibre bundle test were adopted to characterize the combined effects of strain rate and temperature on Kevlar 49 fibre strength distribution. The simulated results are in good agreement with the experimental data, which proves that the bimodal Weibull distribution function is suitable to represent the statistical strength distribution of Kevlar 49 fibre which has peculiar ‘skin–core’ physical structure, and that the test method is valid and reliable.     

Effect of strain rate on the mechanical behaviors of SiC fiber

In the present paper, tensile experiments of SiC fiber bundles under different strain rates (quasi-static: 10^–4–10^–3 s^–1, dynamic: 200–1200 s^–1) are carried out and the corresponding stress-strain curves are obtained. It is found that the mechanical properties of SiC fiber bundles are rate-dependent: the elastic modulus E, strength _b and the failure strain _b remain unchanged under quasi-static condition, while they apparently increase with increasing strain rate under dynamic condition. Based on the fiber bundles model and the statistical theory of fiber strength, a bi-modal Weibull statistical model of the strain rate dependence is adopted to describe the strength distribution of SiC fiber, and the Weibull parameters are obtained by the fiber bundles testing method. Consistency between the simulated and experimental results indicates that the model and the method are valid and reliable.     

针刺C/C-SiC复合材料剪切非线性本构关系

为研究针刺C/C-SiC复合材料的剪切损伤行为,首先,进行了面内剪切加卸载实验,并利用SEM对复合材料的剪切破坏形貌进行了观测;然后,建立了一种塑性与损伤相结合的非线性本构模型描述复合材料的非线性力学行为,以幂函数描述等效塑性应变与等效应力的关系;最后,基于剪切强度的Weibull分布规律提出了一种指数型损伤变量表征剪切刚度的退化,并通过实验数据拟合得到模型中的参数。结果表明:复合材料在卸载后存在明显的残余应变,卸载模量随载荷的增加不断降低,表现出明显的剪切非线性特征;大量无纬布纤维束和纤维单丝拔出,且易在针刺部位发生破坏;由于针刺部位等缺陷的不规律分布,剪切强度存在一定的分散性,符合指数型Weibull统计分布规律;复合材料的剪切非线性主要由基体开裂和纤维/基体界面脱粘等内部损伤引起,从宏观上可以解释为塑性变形和刚度性能折减。所得结论表明本构模型能够很好地表征C/C-SiC复合材料的面内剪切非线性行为。      

Effect of strain rate on tensile behavior of carbon fiber reinforced aluminum laminates

In this paper, the tensile behavior of carbon fiber reinforced aluminum laminates (CRALL) has been determined at a strain rate range from 0.001 s^− 1 to 1200 s^− 1. Experimental results show that CRALL composite is a strain rate sensitive material, and the tensile strength and failure strain both increased with increasing strain rate. A linear strain hardening model has been combined with Weibull distribution function to establish a constitutive equation for CRALL at different strain rates. The analysis of the model shows that the Weibull scale parameter, σ₀, increased with increasing strain rate, but Weibull shape parameter, β, can be regarded as a constant.