共查询到19条相似文献,搜索用时 62 毫秒
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大型锻件在内部孔隙性缺陷锻合后,其疲劳强度等动态载荷力学性能恢复效果是决定锻件质量水平的重要因素之一。采用圆柱试件高温锻合模拟实验,研究了不同的塑性变形工艺下锻件内部孔隙性缺陷修复结合面的组织变化效果,以及对疲劳强度修复的影响。结果表明:仅通过一次镦粗,虽然锻件的内部孔隙性缺陷基本消失,但是由于结合面上组织不均匀、存在细小析出物等,其疲劳性能仅能部分恢复。通过高温条件下两次镦粗加两次拔长工艺,其结合面的疲劳强度基本恢复至初始组织状态对应的性能指标。研究结果为制定合理的锻造工艺、保证锻后疲劳等力学性能恢复至初始状态提供了理论依据。 相似文献
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通过电子显微镜、透射电镜并结合塑性变形数值模拟,观察镁合金铸造缺陷(晶间缩松和缩孔)在变形过程中的形貌变化及缺陷附近应力分布,讨论塑性变形消除铸造缺陷的力学行为,提出镁合金铸造缺陷塑性变形弥合过程为:缺陷体积压缩→界面闭合→界面两侧基体相切变→界面附近再结晶→缺陷部分弥合.结果表明:变形过程中缺陷附近应力集中明显,变形后应力集中大大降低,部分铸造缺陷得以弥合与修复. 相似文献
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在Gleeble-1500热模拟试验机上对Ti-Al-Zr-Sn—Mo—Si—Y合金进行了热压缩试验,采用动态材料模型建立的加工图研究了在变形温度800~1100℃,变形速率在0.002~10s^-1范围内的热变形行为。结果表明:该合金的功率耗散效率的峰值区为875~925℃,应变速率为0.001-0.002s^-1,峰值效率为85%。在温度为900~1000℃,应变速率为0.1~3s^-1的区域和850~950℃,应变速率为0.001-0.01s^-1的环形区域内进行等温压缩,Ti-Al-Zr-Sn-Mo-Si—Y合金发生了动态再结晶,其功率耗散效率为40%~55%。在800~925℃,应变速率为0.03~10s^-1和温度为860~930℃,应变速率为0.003~0.03s^-1区域内易产生流变失稳现象。 相似文献
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搪瓷涂层作为一种惰性涂层,能与大多数金属零部件相容并提供优异的腐蚀防护效果。但搪瓷的高温软化及本征脆性限制了其在高温以及热冲击等苛刻环境下的服役。总结了国内外解决搪瓷涂层烧结温度与服役温度相矛盾、涂层热循环时易剥落等问题的最新进展:首先介绍了通过复合陶瓷颗粒以及对搪瓷/陶瓷界面反应的调控,实现提高涂层使用温度的同时不改变其熔炼和烧结温度的方法体系;接着分析了影响搪瓷涂层抗热震剥落性能的因素(包括搪瓷釉热膨胀系数、涂层/基体界面结合、搪瓷釉力学性能等)。基于搪瓷的硅氧网络基本结构,从热物理性能以及力学性能角度改性等方案仅能在有限范围内提高其抗热震剥落能力的现实,最后提出了发展自修复金属搪瓷高温防护涂层,从根本上解决搪瓷开裂与剥落的问题。 相似文献
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钢锭内部孔隙性缺陷锻合过程的数值模拟 总被引:1,自引:0,他引:1
通过比较圆柱体试样内部孔洞锻合过程的模拟计算结果和实验结果,确立了钢锭内部孔隙性缺陷锻合过程的模拟法,并对长孔型缺陷和短孔型缺陷的锻合过程进行了计算,得到各类孔洞的闭合规律,且定量给出了不同位置处孔洞闭合时所需的临界压下率。从孔洞闭合的力学本质角度,对钢锭内部的等效应变分布情况进行了研究。结果表明,孔洞的闭合完全是由于应力集中并达到一定程度的变形所引起的。其中,四面体孔最难闭合,为所有孔洞锻合所需临界压下率的上限值。锻合区域的给出,为制订锻造工艺提供了理论依据。 相似文献
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针对汽车覆盖件尺寸和重量大,易在悬臂式自动取送料装置放置零件到收料台过程中产生塑性变形的问题,采用Dynaform软件对侧围内板零件进行跌落仿真分析,以便能够在车辆开发阶段判断零件是否存在变形风险。首先,对原始数模在Dynaform中建模仿真,并利用相似零件实物验证了分析的准确性。同时,对零件的风险区域通过增加加强筋进行了设计优化,仿真分析了优化后的零件的跌落过程,通过现场软、硬模分别验证了该跌落仿真的有效性。跌落变形仿真可以在同步工程阶段评估零件在线末收料时是否发生塑性变形,以便及时进行设计优化,避免后期发生工程更改,降低开发成本。 相似文献
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为了研究35CrMoV钢的高温变形行为,借助Gleelble 3800型热模拟试验机,在应变速率为0.01~10 s-1、变形温度为950~1150℃的条件下进行轴向单道次高温压缩试验,并根据试验结果绘制35CrMoV钢的流动应力-应变曲线。分析研究了变形温度、应变速率对流动应力的影响,计算了变形激活能Q及参数n、A、α的取值。试验结果表明:35CrMoV钢在950~1150℃进行压缩试验时,存在动态再结晶和动态回复两种流动应力-应变关系,当应变速率为0.01和0.1 s-1时,其流动应力-应变曲线主要表现为动态再结晶型;当应变速率为1和10 s-1时,其流动应力-应变曲线主要表现为动态回复型。在试验条件下获得35CrMoV钢的平均变形激活能Q为310.433 kJ·mol-1,建立了用于描述35CrMoV钢流动应力、应变速率和变形温度三者之间关系的本构方程。 相似文献
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采用Gleeble-1500热模拟实验机及光学显微镜和透射电子显微镜研究了Ti-47Al-2Cr-0.2Mo(原子分数,%)合金在2.5 s-1,1050~1150℃,道次保温时间分别为1 min、5 min、10 min条件下的多道次热压缩变形行为及其组织演化规律。结果表明,增大道次变形量,合金软化率增大;随着道次间保温时间的延长,合金软化率逐渐增大;变形及保温温度升高,合金软化率提高。动态和亚动态再结晶是合金发生软化的主要原因。再结晶优先发生于层片晶团边界处。随着变形温度升高,γ晶粒内的孪生增多。经过热压缩变形后,组织被细化和均匀化。位错和孪生是主要的变形机制。 相似文献
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Nanocrystallization process and mechanism in a nickel alloy subjected to surface severe plastic deformation 总被引:1,自引:0,他引:1
Bulk components made of a Ni-base C-2000 alloy with a face-centered cubic crystal structure and a very low stacking fault energy have been severely plastically deformed at the surface region to attain a grain size gradient ranging from nanocrystalline at the surface to coarse grained in the bulk. The evolution of microstructural characteristics has been studied as a function of the processing time employing a variety of analytical techniques, including extensive conventional and high-resolution transmission electron microscopy analyses. The thickness of the nanocrystalline surface layer is found to increase with the processing time. Deformation twinning is ubiquitous and occurs at the earliest stage of deformation and the deepest region of the material where plastic deformation has taken place in the surface severe plastic deformation process. A grain-refinement mechanism led by deformation twins and complemented by dislocation activity has been put forth to explain the nanocrystallization of the coarse-grained material employed in this investigation. 相似文献
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TC4ELI合金疲劳裂纹尖端塑性区对裂纹扩展的影响 总被引:1,自引:1,他引:1
研究了TC4ELI合金片层组织与短棒α组织中的疲劳裂纹尖端塑性区及裂纹扩展行为.首先通过SEM及TEM观察比较两种显微组织下的疲劳裂纹尖端塑性区,讨论两种显微组织中裂纹尖端塑性区对疲劳裂纹扩展路径及扩展断口的影响,分析裂纹扩展路径和裂纹尖端塑性区对裂纹闭合及裂纹扩展速率的影响.结果表明:与短棒α组织相比,片层组织中具有较大的裂纹尖端塑性区及曲折的裂纹扩展路径,并最终从疲劳裂纹闭合的角度,解释了片层组织具有较低的疲劳裂纹扩展速率的原因. 相似文献
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爆炸焊接波状结合区塑性变形机理的计算分析 总被引:1,自引:0,他引:1
爆炸焊接结合区产生大的塑性变形及波状结合,是爆炸焊接工艺的主要特征,也是实现良好冶金结合的必要条件。但是,塑性变形及波状结合的形成机理尚不明确。该文引入牛顿应力公式到弹塑性模型,以近似描述结合区材料行为,建立了连续介质模型,对波状结合区的塑性变形及爆轰速度对塑性变形的影响进行计算分析,并与试验结果对比。结果表明,结合界面呈波形,结合区材料产生大量的塑性变形,并且向界面集中,变形集中的区域沿爆轰方向由宽变窄,材料变形量逐渐增大;随着爆轰速度的增大,界面变形区域扩大,且变形量增大。 相似文献
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Chunguo Zhang Xiaozhi Hu Pengmin Lu Gaiping Zhang 《Journal of Materials Processing Technology》2013,213(11):2005-2014
The effects of tensile over-load (OL) on fatigue crack growth behavior of a weld-repaired high-strength low-alloy (HSLA) steel were studied by measuring both the fatigue crack growth rate and sample-thickness variation along the fatigue crack growth path. The thickness variation, indicating the degree of plastic deformation (PD), provided an indirect measurement of associated residual compressive stresses at the crack-tip. The applied tensile OL with one-hour holding period in each test generated a damage zone at the crack tip. Microscopic details of the crack-tip damage zone were characterized by scanning electron microscopy. Three groups of expanded compact-tension (E-CT) samples, 10 mm in thickness, were tested: weld-repaired HSLA without soft buffer layer (BL), and weld-repaired HSLA with 4 mm or 10 mm thick BL. The experimental results showed that the OL-induced PD, closely linked to the crack-tip residual compressive stresses, reduced the subsequent fatigue crack growth rate, and that the HSLA with a 10 mm BL had the lowest growth rate, indicating a soft BL with an adequate thickness could further improve the fatigue resistance. 相似文献
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Kozo Ikegami Yo Shirasawa Tomohito Yokotsuka Yasushi Niitsu 《Metals and Materials International》1998,4(4):899-903
Cyclic plastic deformation of stainless steel SUS 304 is experimentally investigated at low temperature of liquid nitrogen
(77 K) under various cyclic loading conditions Thin walled tubular specimens are subjected to cyclic loading under constant
strain ranges. At low temperature, the material shows remarkable hardening by cyclic loading comparing with cyclic loading
at room temperature. The hysteresis curves of stress-strain relations by cyclic loading are saturated by increasing the cycle
numbers. The saturation tendency depends on loading direction. The saturated stress values are related with cumulative plastic
strain of cyclic loading. The prestraining is given at 77 K by axial and torsional loadings, and subsequent cyclic loading
under constant strain range is conducted at 77 K. The cyclic stress-strain curves are saturated by increasing cyclic numbers.
At small cyclic numbers, cyclic plastic deformation depends on the prestrain direction. The directional effect of pre-strain
on cyclic loading becomes small with increasing number of cycles. 相似文献