【作者】 金兰；

【导师】 李维娟；

【作者基本信息】 辽宁科技大学 ， 材料加工工程， 2012， 硕士

【摘要】 本文研究了不同加载方式下的预应变对超低碳钢烘烤硬化性能的影响。利用烘烤箱对试样进行170℃×20min的烘烤处理,通过MTS810万能试验机进行烘烤前的预变形和烘烤硬化性能测定,采用透射电镜对不同预应变方式下和烘烤后的位错形貌进行观察,同时应用ANSYS有限元软件对不同预应变方式下的应力应变情况进行模拟,得到如下结论:（1）采用标准拉伸试样进行单向拉伸预变形的情况下:在0%⁴%范围内,随着预应变的增大,BH值增大;在4%⁸%范围内时,随着预应变的增大,BH值降低,且4%预应变所对应的BH值最大;而在8%¹5%范围内,随着预应变的增大,BH值又有所提高,8%预应变所对应的BH值最小;4%预应变时的位错密度明显大于8%时的位错密度,而且变形程度越大,位错分布不均匀性程度越大;通过数值模拟发现在预应变较小时,模拟的结果与真实的结果相接近,而预应变较大时,误差较大,但是应力应变在标距内分布均匀。（2）采用宽板试样（b/t>30,b为宽度,t为厚度）进行单向拉伸,以产生平面变形的预变形情况下:随着预应变的增加,BH值也增加,但是与标准单向拉伸时的BH结果明显不同,其变化幅度比较小;在此条件下的位错密度明显小于标准单向拉伸情况下的位错密度;数值模拟表明,虽然实际上加载的预应变大小与标准单向拉伸时的相同,但是材料内部产生的塑性变形远远小于实际加载量,且亦小于标准单向拉伸时产生的塑性变形量。（3）采用十字拉伸试样以产生双向变形的预变形情况下,一个方向始终加载2%预应变,另一个方向分别加载1%,2%,3%和4%预应变,以实现不同加载比,根据单向拉伸情况下的BH值定义两个值,BH0和BH₂,结果表明:随着加载比的增加,BH0和BH₂两个值都有所增加;试样内部的位错密度也在不断地增加;数值模拟发现,应力应变分布具有一定的方向性,即应力应变分布的弯曲部位弯向加载大的方向。更多还原

【Abstract】 The effect of pre-strain, under different loading path, on the baking hardening property for ultra-low carbon steel was studied in this paper. The samples were baked at 170℃for 20min in the oven, the pre-strained applied and bake-hardening performance measurement was carried out on the MTS810 universal test machine, and the dislocations morphology with different pre-strain style and baking was observed by the transmission electron microscopy. at the same time, the stress and strain with different pre-strain method was simulated with ANSYS software. The conclusions are as follows:（1） Under the condition of uniaxial tensile deformation that standard tensile specimen was adopted: in the range of 0% 4%, the BH value increased along with pre-strain increased; In the range of 4% 8%, the BH value decreased along with the increase of the pre-strain, and the BH value corresponding to 4% was highest; And in the range of 8% 15%, BH value improved along with the increase of the pre-strain, and the BH value corresponding to 8% reached minimum; The dislocation density of 4% was significantly larger than that of 8%, and the greater the deformation was, the greater of dislocation distribution uniformity was; And the smaller the pre-strain was, the closer of the simulated results to true ones, which was showed in the numerical simulation, however the higher the pre-strain became, the bigger the error was, but stress and strain distribution within the gauge was uniform.（2） In the case of wide plate sample （b/t > 30, b represent for width, t represent for thickness） to generate the plane deformation: the BH value increased with the increase of the pre-strain, but the magnitude was smaller than uniaxial tensile results; And the dislocation density was obviously less than that of uniaxial tension; Numerical simulation results showed that although the real pre-strain applied in the wide plate sample was similar to the uniaxial tension, the plastic deformation generated in the material was far less than the actual load, and also less than that of the uniaxial tensile samples.（3） In the case that cross tensile samples used to produce two-way deformation, 2% pre-strain always applied on one direction, and different pre-strain applied on another one, 1%, 2%, 3% and 4% respectively, so that the different loading ratio achieved. and two values, BH0 and BH₂ were defined according to uniaxial tensile of BH value, the results showed that, both BH0 and BH₂ increased with the increase of loading ratio; and dislocation density of sample was increased; Numerical simulation results showed that the distribution of stress and strain was directivity, namely the larger the load was,the higher the strain was.更多还原