共查询到19条相似文献，搜索用时 234 毫秒
1.
《武汉工程职业技术学院学报》2017,(3)
基于等离子喷涂涂层显微组织图片构建有限元模型,准确反映孔洞、裂纹等缺陷在涂层中的实际分布特征。利用LS-DYNA有限元方法计算拉伸过程中涂层内部的应力变化,以最大主应力作为涂层材料的失效判据,模拟裂纹萌生、扩展过程。数值模拟结果表明,喷涂过程中在陶瓷层内形成的横向主裂纹尖端是拉伸过程中裂纹扩展的萌生点,裂纹在扩展过程中与原有缺陷相互作用使得扩展的裂纹发生了分叉以及偏转,真实再现了裂纹扩展引起涂层失效的过程。 相似文献
2.
《浙江大学学报(A卷英文版)》2020,(4)
本文综述了择优取向纳米孪晶金属中"链式"关联位错(CNDs)的研究进展。当拉伸方向与孪晶界方向水平,且孪晶厚度(λ)为1 nm左右时,关联位错会大量开动,引起材料持续强化。在较宽的孪晶片层中,裂纹等初始缺陷可引起应力集中,诱发关联位错形核。此外,循环变形也会促进关联位错在纳米孪晶结构中的形成,使后者具有与历史无关、稳定和拉压对称的循环响应。最后,本文提出了择优取向纳米孪晶金属中与"链式"关联位错相关的潜在研究方向。 相似文献
3.
覃之光 《武汉工程职业技术学院学报》2012,24(2):25-28
通过对82B高碳钢线材开卷断裂的断口形貌观察及金相组织分析,认为线材开卷断裂是由于线材中心马氏体的转变与表面损伤共同作用的结果,导致线材表面承受拉应力,该拉应力可促使线材表面形变马氏体产生的微裂纹迅速扩展,直至断丝。防止开卷断裂就需要从控制中心马氏体及表面损伤等两方面采取措施。 相似文献
4.
对TC4钛合金试样拉伸疲劳断裂宏观试验结果、相应的断口和卸载表面观察分析研究,发现在试样断口上有明显的河流花纹走向、韧窝和韧性条带特征.其断裂机理是疲劳拉伸载荷作用下,在应力值比较高时一些沿层裂纹开始出现并扩展,同时微孔长大形成韧窝,并最后导致了材料断裂. 相似文献
5.
应用MTS试验机进行了贝氏体钢轨钢裂纹扩展速率试验,利用Paris公式分析了贝氏体钢轨钢裂纹扩展速率试验数据,结果表明:可以利用Paris公式获得的疲劳裂纹扩展速率公式计算指定应力强度因子幅下裂纹扩展速率。 相似文献
6.
万文红 《马钢职工大学学报》2013,(3):13-15,22
捅善芒：采用化学分析、金相检验等分析方法,对4Cr13不锈钢模具在使用中发生开裂的原因进行了分析。模具的内壁离断裂面不远处有一条横裂纹,裂纹长40ram,裂纹中间有小孔洞存在。分析结果表明：4Cr13模具组织中有大量共晶碳化物是导致裂纹产生的主要原因。通过改进4Cr13钢的冶炼、浇注,锻造工艺,减少钢锭中碳化物量,可以消除4Cr13模具中共晶碳化物缺陷,使其裂纹发生率降低。关键词：4Cr13模具;共晶碳化物;裂纹中图分类号：TF764．1文献标识码：B文章编号：1672—9994（2013）03—0013一03 相似文献
7.
本文主要研究了铸造A356铝合金的拉伸性能以及断口的形态和产生断口的原因,从不同位置处观察和分析并进行了相关试验.铸造A356铝合金的拉伸屈服强度随离浇道口平面距离的增加而减小,断裂强度则是先减小然后再增大,而延伸率随高度变化不明显.其断口有着孔洞、杂质、氧化膜和铸造缩孔等缺陷,表面也存在由C、O、Fe、Mg、Al和Si元素形成的复合粒子,并对其进行了分析及研究. 相似文献
8.
该文的主要目的是利用英国剑桥S250MK-Ⅱ扫描电镜,对高温多轴疲劳试样的断口形貌特征进行系统地扫描观察。结果表明,裂纹萌生于试件缺口根部最外层,起始于材料缺陷,试样加工刀痕,以及材料组织内部的脆性颗粒等附近,并呈现萌生裂纹的多源性;疲劳裂纹扩展区疲劳条纹为沿圆周方向被撕断的、不连续的条纹,而不是疲劳条带,并伴随着二次疲劳裂纹的出现;在瞬间断裂区,随着非比例度的增加,在瞬间断裂时韧窝逐渐加深,且撕裂面逐渐加大,且晶内第二相强化粒子Ni3Al是产生韧窝的主要根源。 相似文献
9.
通过对圆柱体直前缘表面裂纹在循环拉伸与循环扭转载荷共同作用下的扩展规律进行实验研究,分析了不同载荷曲线相位差、以及拉扭应力幅度对表面裂纹扩展路径、疲劳寿命和裂纹扩展速率的影响。结果表明:不同的相位差对裂纹扩展行为有着非常重要的影响。初始阶段的裂纹扩展主要受到剪应力幅度的影响,后继扩展则依赖于轴向应力幅度。拉应力和剪应力的增加均会增加裂纹扩展速率,但轴向应力幅度变化的影响大于剪切应力幅度。 相似文献
10.
本篇文章研究了影响铝合金疲劳性的多种因素,其中着重论述了分析了加载路径对试件疲劳性能的影响机理.另外此研究表明:不同加载路径下断口特征以有明显的碳化区,其裂纹主要是从试件内部夹杂物处产生;另外此研究还发现加载路径不同,位错密度越大,位错结构不同,抗变形能力越强,疲劳寿命越短.其中椭圆形的位错密度小于矩形小于正方形小于圆形. 相似文献
11.
李红英 《雁北师范学院学报》2011,27(1)
提出了金属拉伸试样断口分析方法,讨论了试样在拉伸试验中的应力分布、断裂过程以及影响断口形貌的因素,为断裂形态分类和断裂原因分析提供了重要依据。 相似文献
12.
13.
Fatigue and fracture behavior of nickel-based superalloy Inconel 718 up to the very high cycle regime 总被引：2，自引：0，他引：2
Xian-feng Ma Zheng Duan Hui-ji Shi Ryosuke Murai Eiichi Yanagisawa 《浙江大学学报(A卷英文版)》2010,11(10):727-737
The fatigue and fracture behavior of nickel-based superalloy Inconel 718 was investigated up to the very high cycle regime under rotary bending tests at room temperature. It was found that this superalloy can still fracture after exceeding 107 cycles. Fractographic analysis revealed that there was a transition from fatigue crack initiation at multi-sites to single initiation with decreasing stress levels. The fracture surface can be divided into four areas according to the appearance, associated with fracture mechanics analysis of the corresponding stress intensity factors. The fracture mechanism dominant in each area was disclosed by scanning electron microscope examination and analyzed in comparison with those obtained from the crack growth tests. Subsequently, life prediction modeling was proposed by estimating the crack initiation and propagation stage respectively. It was found that Chan （2003）＇s model for initiation life and the Paris law for growth life can provide comparable predictions against the experimental life. 相似文献
14.
Probabilistic analysis of linear elastic cracked structures 总被引：1，自引：0，他引：1
AKRAMIN M.R.M ALSHOAIBI Abdulnaser HADI M.S.A. ARIFFIN A.K. MOHAMED N.A.N. 《浙江大学学报(A卷英文版)》2007,8(11):1795-1799
This paper presents a probabilistic methodology for linear fracture mechanics analysis of cracked structures. The main focus is on probabilistic aspect related to the nature of crack in material. The methodology involves finite element analysis; sta- tistical models for uncertainty in material properties, crack size, fracture toughness and loads; and standard reliability methods for evaluating probabilistic characteristics of linear elastic fracture parameter. The uncertainty in the crack size can have a significant effect on the probability of failure, particularly when the crack size has a large coefficient of variation. Numerical example is presented to show that probabilistic methodology based on Monte Carlo simulation provides accurate estimates of failure prob- ability for use in linear elastic fracture mechanics. 相似文献
15.
The fracture processes of concrete were described by a cohesive crack model based on initial toughness criterion. The corresponding analytical method to predict the instability state was proposed. In this model, the initial toughness was adopted as the crack propagation criterion and the weight function method was used to calculate the stress intensity factor and the crack opening displacement caused by the cohesive stress. The unstable toughness can be easily obtained using the proposed method without measuring parameters at the critical state that was necessary in traditional methods. The proposed method was verified by existing experimental data of wedge splitting specimens with different grades of concrete and the sensitivity of the results on the tensile softening curve was discussed. The results demonstrate that the proposed method can well predict the peak load, the critical effective crack length, and the unstable toughness of concrete specimens. Moreover, the calculated unstable toughness is not sensitive to the tensile softening curve. 相似文献
16.
熊焰 《武汉工程职业技术学院学报》2011,(3):37-39
用光学金相显微镜等分析手段,对30MnSi钢筋镦头断裂原因进行了分析。结果表明：断裂钢筋中存在的表面缺陷、夹渣以及成分偏析是导致钢筋断裂的主要原因。 相似文献
17.
18.
Calculation Model of Equivalent Strength for Induced Crack Based on Double-K Fracture Theory and Its Optimizing Setting in RCC Arch Dam 总被引：2，自引：0，他引：2
By means of fracture testing on roller-compacted concrete (RCC) three-point bending beams with two different specimen sizes, the P-CMOD complete curve for RCC was gained. Furthermore, by applying double-K fracture theory, KIC^ini,KIC^un, as well as the critical effective crack length and the critical crack tip opening displacement, were evaluated. Based on the double-K fracture parameters above, the calculation model of equivalent strength for induced crack was established, thus the calculation method on its initiation, stable propagation and unstable fracture was ascertained. Moreover, the finite element simulation analysis of stress field in ShaPai arch dam and the on-site observational splaying points of induced crack at different altitudes validated the reliability of the model. Finally, crack inducer‘s optimal setting in RCC arch dam was studied. It improves the design level of induced crack in RCC arch dam and satisfies the necessity of engineering practice. 相似文献
19.
A newly developed pure rolling fatigue test rig with three contact points for bearing balls was used to perform rolling contact fatigue (RCF) tests. The fatigue properties of GCr15 steel balls and two kinds of Si3N4 ceramic balls (GSN-200 and NBD-200) produced with different technologies were compared. Ball surfaces were examined after failure with optical microscope and scanning electron microscope (SEM). It was identified by tests that the failure mode of ceramic balls was surface spall. The main factor of ceramic ball failure was principal tensile stress. Life tests data, summarized in accordance with the Weibull theory, showed that the life of GSN-200 balls was close to that of GCr15 balls, whereas the life of NBD-200balls was much longer than those of GSN-200 and GCr15. Under the same working condition, the temperature rise of all ceramic balls was lower than that of steel balls, and their crack propagation rates were slower than that of steel balls. 相似文献