钢板断后伸长率测量不确定度的评定

为评定钢板断后伸长率的测量不确定度,以轧制厚度为18mm的Q235B板材矩形带头短比例试样为 例,建立了不确定度计算的数学模型,确定了影响试验结果的各项因素:如断后标距Lu、原始标距L0,计算出了各因素的标准不确定度,得出结果的扩展不确定度,并给出最终测量结果的表达式:断后伸长率的最终测量结果为 (28±3)%。     

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简要介绍了伸长率换算标准,并探求了其在力学检验中的实际应用。实际应用中将钢材试样的原始标距设为一固定值,然后测量断后标距,利用Oliver换算公式作为转换工具,通过计算机的便捷性换算得出符合标准要求的断后伸长率。证明了其在实际应用中的方便性和可行性,并就应用中的误差进行了分析。     

用重量法求无标记试样伸长率

拉伸试验时,试样因标距打点不清,或断在标点以外,试样断后的伸长测不出来,按规定应补做试验。我们利用重量法来予以补救,求出其伸长率。其珲论依据是拉伸前后的重量不变。方法如下:把拉断后的试样对接起来,在断口两边,取一定长度L,称其重量,设这一段的重量为P_0。利用已知的试样原始面积F_0和比重D_0来求出此段试样拉断前的长度L_1 L_1=P_0/D_0·F_0 (1) 如果计算出来的L_1等于试样原标距长度L_0,     

室温拉伸试样尺寸的变化对力学性能参数值的影响

通过试验研究了45~#钢板不同拉伸板型试样(宽度改变)的拉伸性能。试验表明:板状拉伸试样变化对拉伸结果有一定的影响,屈服强度根据截面积的变化而稍有改变,抗拉强度则基本保持不变。分析认为,与标准拉伸尺寸相比,板型拉伸试样的抗拉强度与试样尺寸关系不大,屈服强度略有不同,伸长率受原始标距和平行长度的影响,建议测定断后伸长率时标明具体的原始标距长度数值,板型拉伸选取试样宽度与板材厚度接近为宜。     

变形速度／试样尺寸对断后伸长率的影响

本文通过对板材拉伸试样在不同变形速度和不同试样尺寸下所测得的断后伸长率的分析,阐述了变形速度及试样尺寸对伸长率的影响。伸长率是衡量钢材的塑性指标之一。在室温下,对试样进行拉伸,而后由公式δ=(L—L_0)/L_0×100测定伸长率。试验方案:从苏联进口的钢板(厚度为2.6mm)上取纵向样(标点距离L=50mm,平行部长度P≈60mm,宽度W=25mm,肩部半径R≥15mm,厚度为2.6mm),按JIS Z 2201制成13A试样(宽度W=20mm,平行部长度分别为P≈135mm,肩部半径R=25mm,被夹部宽度B=25mm,标     

断后伸长率的换算法

本方法通过测试最大应力下的非比例伸长率和断后伸长率,求得与材料相关的常数α、β的值,然后就可以根据公式δ=α+β(S_o~(1/2))/ l_o换算出该材料其他任何标距试样的断后伸长率了。该法不受材料的种类和试样尺寸的限制,只要形状相似均可换算,具有通用性。     

国产Q420D低合金高强度钢的高温拉伸性能

通过对国产Q420D低合金高强度钢进行高温(200～800℃)拉伸试验，得到在不同试验温度下的弹性模量、屈服强度、抗拉强度、断后伸长率以及应力-应变关系，建立了多项式模型、NIST模型和Ramberg-Osgood (R-O)模型，并与国内外的钢结构抗火设计规范进行对比。利用多项式模型和NIST模型对力学参数的折减系数进行拟合；根据不同温度下的应力-应变曲线，基于R-O模型拟合得到Q420D钢的应力-应变本构模型。结果表明，在200～400℃,Q420D钢的强度、弹性模量和断后伸长率与室温相比下降幅度较小﹐温度超过400℃后，其强度和弹性模量下降速率明显加快，断后伸长率急剧增大。     

5A90铝锂合金电子束焊焊板超塑性变形力学行为

通过高温拉伸试验研究了5A90铝锂合金电子束焊焊板超塑性变形行为. 结果表明,5A90铝锂合金电子束焊焊板具有良好的超塑性变形能力,焊板的峰值流变应力随温度升高及初始应变速率的减小而减小,应变速率小于1×10-2/s时,焊板峰值流变应力小于32 MPa;焊板的断后伸长率随温度的升高和初始应变速率的增大而先增大再减小,在450℃,5×10-3/s断后伸长率达到最大为171.1%. 提出变形比例系数K（接头与母材断后伸长率的比值）,评价焊板中接头的超塑性变形协调能力,在各变形条件下K值均达到70%以上.     

Fe-Mn-Al轻质高强钢组织和力学性能研究

对热轧态与固溶处理后Fe-Mn-Al轻质高强钢进行力学性能检测及组织形貌观察,分析950~1100℃固溶处理工艺对其组织和力学性能的影响规律,根据真实应力-应变曲线和加工硬化曲线分析拉伸变形特征,对比拉伸变形前后微观组织形貌和XRD谱,研究其微观变形机理.研究结果表明,所设计的成分体系实验用钢,热轧后为奥氏体基体与少量带状铁素体的双相组织,密度为6.55 g/cm3,达到了轻质高强的设计目标.固溶处理有利于奥氏体晶粒长大与带状铁素体的破碎分解,使钢板强度降低而塑性提高,但是过高的固溶温度会促进铁素体长大,使铁素体体积分数增大,钢的断后伸长率降低.1050℃固溶处理后Fe-Mn-Al钢抗拉强度为925.9 MPa,断后伸长率为50.20%,强塑积为46.48 GPa·%.连续的应变强化行为使得Fe-Mn-Al钢获得高强度与塑性的良好匹配,稳定硬化阶段应变范围越宽,断后伸长率越大;较高的层错能使其变形机理区别于TRIP和TWIP效应,变形后仍为奥氏体+铁素体双相组织,变形后奥氏体中可以观察到Taylor晶格、高密度位错墙以及微带结构,为明显的平面滑移特征.     

21-4N气门钢高温压缩变形行为

采用圆柱试样在Gleeble-1500D热模拟试验机上进行高温压缩变形模拟试验,变形温度800～1100℃,应变速率为0.005～1 s-1,研究了5Cr21Mn9Ni4N(21-4N)气门钢的高温塑性变形行为。结果表明,在21-4N气门钢高温压缩变形时,应变速率和变形温度的变化强烈影响着合金的流动应力,它随变形速率的升高而增大,随变形温度的升高而降低;高温变形条件下流动应力σ、应变速率觶ε和变形温度T之间满足一定关系,它可为电镦工艺参数的优化和数值模拟提供依据。     

热影响区几何尺寸对铝合金焊接接头变形及强度影响规律

用有限元软件ABAQUS对平板对接铝合金焊接接头进行拉伸模拟,研究了HAZ几何尺寸对焊接接头变形及强度影响规律.结果表明,随着HAZ长度的增加,铝合金焊接接头的屈服强度和抗拉强度均逐渐降低,应力三轴度在母材与HAZ交界处和焊缝与HAZ交界处存在突变,应力三轴度最大值的位置从母材与HAZ交界处转变为焊缝与HAZ的交界处;随着接头厚度的增加,屈服强度和抗拉强度基本上是逐渐增大的,接头中的应力三轴度取决于试样的厚度、焊缝区尺寸及HAZ尺寸;随着接头宽度及标距长度的增加,屈服强度、抗拉强度和焊缝及HAZ范围内的应力三轴度基本上是逐渐增大的.当试样标距长度增加到某一值时,这三个参数将不再发生变化,为一恒值.     

Creep and tensile properties of press molding joined GMT-sheets

GMT-sheet is used in automobile bumper with high rigidity and strength, and its joining strength is influenced by lap length, one of the joined molding conditions. Fracture strength was calculated by dividing fracture load with cross-sectional area. Total five repeated measurements were made to obtain the average value. Tensile test was conducted at room temperature for 10 specimens. In addition, the effect of compression ratio on creep and tensile performance during lap joined molding was discussed. With increasing lap length, the lap joining efficiency of GMT-sheet was increased. However, higher compression ratio reduced the joining efficiency. Creep test on GMT-sheet showed abrupt fracture without tertiary creep. This can be explained by the weak thermal resistance of the resin. If GMT-sheet was exposed to high temperature for a long time, it was easily failed by external force.     

抗塌陷钎焊铝复合箔的生产技术

汽车空调器中的蒸发器和冷凝器所用铝复合箔正朝着越来越薄的方向发展，这就要求开发出强度高、钎焊温度下抗塌陷能力强的新型复合材料，以满足市场的需要，对已稳定生产的新型钎焊铝复合材料作了简要介绍。     

热镀锌双相钢点焊结构的临界试样厚度

针对热镀锌双相钢DP600电阻点焊结构的分界面断裂失效,利用统计分析方法,研究了不同熔核长度(5～8 mm)下,板厚分别为0.8 mm和1.5 mm的DP600点焊结构拉剪测试失效模式,建立DP600点焊结构发生分界面断裂失效的概率与熔核长度和板厚的关系模型,从而确定其临界试样厚度,以及熔核长度对临界试样厚度的影响.结果表明,熔核长度和板厚对DP600点焊结构分界面断裂失效的影响较大;随着熔核长度的递增,临界试样厚度呈线性增加.研究结果可为车身用高强钢电阻点焊结构的优化提供指导.     

Study on Anisotropic Mechanical Properties of Cold Drawn Pearlitic Steel WireEI北大核心CSCD

Cold drawn pearlitic steel wires with ultra-high strength are widely applied in industrial fields such as bridge cables, automobile tire and springs rope. In recent years, the strengthening mechanism and microstructure evolution have been profoundly studied. In order to investigate the influence of microstructure evolution on mechanical properties, the anisotropic mechanical properties of cold drawn pearlitic steel wires were investigated by tensile test, SEM and TEM. Results indicated that the distinctions of tensile strength between three directions (parallel to the tensile axis, inclined to the tensile axis (45 degrees), vertical to the tensile axis) were amplified with increasing strain. The effect of strain strengthening was observed in parallel and inclined directions while the vertical direction remained strength stability in 1320 MPa. The wire rod was isotropic and the fracture mode was transgranular fracture; After cold drawing, the tensile strength reached peaks in parallel direction and valleys in vertical direction. The fracture mechanism of inclined and vertical directions remained transgranular or intergranular fracture while the fracture mechanism of parallel direction was converted into microvoid accumulation fracture. In TEM, the phenomenon was discovered that due to non-homogeneous distribution in vertical direction, dislocations piled up at the boundaries resulting in stress concentration. On the contrary, the dislocations were uniformly distributed which led to homogeneous transformation in parallel direction.     

电子束快速成形TC18钛合金柱状晶组织的拉伸性能

采用电子束快速成形方法,获得了一种TC18钛合金的柱状晶组织,研究了热处理工艺对该类组织析出相和拉伸性能的影响。结果表明,在740～830℃温度范围内固溶、在550℃时效处理,随着固溶温度的升高,快速成形样品沿柱状晶方向的强度呈上升趋势,塑性呈下降趋势;在830℃固溶处理后,在550～650℃时效温度范围内,随着时效温度的升高,沿柱状晶方向的强度呈下降趋势,而塑性呈上升趋势;拉伸性能随热处理工艺的变化主要取决于热处理过程中产生的二次α相;发现了延性韧窝和沿晶+准解理两种不同类型的断口形貌,并对其形成原因进行了分析。     

Effect of tool geometry on microstructure and static strength in friction stir spot welded aluminium alloys

The effect of tool geometry on microstructure and static strength in friction stir spot welds of 6061 aluminium alloy sheets was studied. Tools with three different probe lengths were used to join the aluminium sheet with different tool rotational speeds and tool holding times. The weld microstructures varied significantly depending on probe length, tool rotational speed and tool holding time. Two particular aspects were identified: the thickness of the upper sheet under the shoulder indentation and the nugget size. The former decreased with increasing probe length at the shortest tool holding time and the slowest tool rotational speed, but there were no discernible differences in other welding conditions, while the latter increased with increasing probe length, tool rotational speed and tool holding time. The tensile shear strength increased with increasing probe length, while the cross-tension strength was not affected significantly by probe length. Two fracture modes were observed: shear fracture of the nugget and mixed mode fracture under tensile shear loading, and nugget debonding and pull-out under cross-tension loading. Based on experimental observation of the microstructures, the effect of probe length on static strength and the fracture mechanisms were discussed.     

超级钢板材冲压性能的试验研究

超级钢的化学成分与普通的碳素结构钢相近,但其力学性能有大幅度的提高.将超级钢应用于国产汽车冲压件的生产中不仅可以提高汽车质量,而且可以降低汽车的成本、减小汽车重量、降低能源消耗和减少环境污染.概述了板材的冲压性能的评价指标,介绍了拉伸试验值对板材冲压性能的影响,对超级钢板材进行了拉伸试验、冷弯试验和金相组织检验,研究了超级钢板的硬化指数、塑性应变比、屈服强度、极限强度、均匀延伸率等力学性能,并分析了超级钢板的冲压成形性能,了解这些性能对超级钢冲压件的生产具有一定的指导作用.     

Creep and tensile properties of press molding joined GMT-sheets

GMT-sheet is used in automobile bumper with high rigidity and strength, and its joining strength is influenced by lap length, one of the joined molding conditions. Fracture strength was calculated by dividing fracture load with cross-sectional area. Total five repeated measurements were made to obtain the average value. Tensile test was conducted at room temperature for 10 specimens. In addition, the effect of compression ratio on creep and tensile performance during lap joined molding was discussed. With increasing lap length, the lap joining efficiency of GMT-sheet was increased. However, higher compression ratio reduced the joining efficiency. Creep test on GMT-sheet showed abrupt fracture without tertiary creep. This can be explained by the weak thermal resistance of the resin. If GMT-sheet was exposed to high temperature for a long time, it was easily failed by external force.     

热轧卷取温度对HC340LAD+Z带钢力学性能的影响

为了研究热轧卷取温度对热镀锌HC340LAD+Z带钢力学性能的影响规律,对同一炉次、相同规格的3批次钢坯,分别采用580、620、660 ℃3个卷取温度,以及相同的冷轧、热镀锌、退火工艺进行了试验研究。结果表明,随着卷取温度的升高,成品带钢的屈服强度、抗拉强度降低,伸长率稍有增加,均满足EN10346标准对HC340LAD+Z带钢力学性能的要求。热轧卷取温度为620 ℃时,HC340LAD+Z带钢的屈服强度为389.2 MPa,抗拉强度为474.3 MPa,伸长率A80为26.5%,其综合力学性能对比标准指标,富裕量最佳。