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1.
对调质42CrMo钢进行室温下各种应力循环和对称应变循环的低周疲劳实验,揭示材料的循环软化特性,棘轮变形和低周疲劳特性以及棘轮-疲劳交互作用。结果表明,调质42CrMo钢体现出明显的循环软化;在应力幅值或平均应力较高时,试样的棘轮变形较大,其破坏形式为延性破坏,而在应力水平较低时,材料的破坏由疲劳裂纹扩展所致的脆性断裂引起;材料在应力循环下的低周疲劳寿命由于有棘轮变形的产生而受到平均应力、应力幅值、最大应力和应变比等多种因素的影响。 相似文献
2.
Brittle cracks were observed in the welded beam-to-column connections of steel frames during an earthquake. The crack propagation and accumulated damage to the connections can lead to fractures at much lower ductility ratios. Understanding the connections’ damage behavior during an earthquake is crucial for the design of steel moment frames in seismic areas. Nine full scale beam-to-column connections were tested under constant amplitude and variable amplitude cyclic loading. The effects of loading amplitude, loading history, and peak load on the connection damage were analyzed. The damage characters were studied and three damage evolution models were calibrated and validated based on test results. The damage mechanism was investigated and an effective plastic strain index was developed to evaluate connection damage based on a ductile fracture mechanism. A fatigue fracture mechanics-based model, for evaluating the damage process of beam-to-column connections under cyclic loading, was proposed. 相似文献
3.
Through the experiments of 7 T-section composite beams, steel fiber reinforced self-stressing concrete （SFRSC） as the composite beam in the composite layer was studied under the hogging bending. The tests simulated composite layer tensile strain under the hogging bending of inverted loading composite beams, giving the relationship under the different fatigue stress ratios between fatigue cycles and steel bar’s stress range, crack width, stiffness loss and damage, etc., in composite layer. This article established fatigue life equation, and analyzed SFRSC reinforced mechanism to crack width and stiffness loss. The results show that SFRSC as the composite beam concrete has excellent properties of crack resistance and tensile, can reinforce the fatigue crack width and stiffness loss of composite beams, and improve the durability and in normal use of composite beams in the hogging bending zone. 相似文献
4.
N2 and N3 are known as the transition points of the three principal stages of fatigue： initial accommodation, accretion of damage and terminal fatigue. Many experiments show that the ratios of N2/Nf and N3/Nf tend to be stable even though the specific N2 and N3 values may fluctuate widely. The primary goal of this research is to study the piezomagnetic field surrounding AISI 1018 steel specimen under repeated loads and to find the ratio values of N2/Nf and N3/Nf by analyzing 11 sets of low-cycle fatigue data. An MTS-810 testing system with a peak capacity of 222 kN was used to obtain the data which consisted of stress, strain, and piezomagnetic field. A computer program was constructed to track the evolution of the piezomagnetic field and regression analysis was carried out to determine N2 and N3 values. It was observed that there exists a consistent relationship between N2 and Nf. The apparent invariance of the ratio N2/Nf implies that N2 may be identified as an index of performance in the early loading response of a specimen that forecasts its fatigue life, Nf. It has been demonstrated that measurements of the magnetic and mechanical hysteresis can yield significant insights into the various stages of the development of a fatigue critical microstructure which culminates in complete rupture of the material. 相似文献
5.
选取两种不同规格的玻璃纤维土工格栅,首先进行大量的静载强度试验,在此基础上,进行了不同应力水平下的恒幅疲劳试验,研究玻璃纤维土工格栅的P-S-N曲线、滞回曲线以及应变与循环次数的关系。结果表明:玻璃纤维土工格栅的应力-寿命关系可以用幂函数来拟合,其疲劳性能具有明显的脆性材料的特性,疲劳寿命较低;玻璃纤维土工格栅的应变-循环比特性曲线呈现出三阶段变化规律,第一阶段为循环的20%之前,应变增加较快,第二阶段为循环的20%~80%之间,应变变化平缓,第三阶段为循环的80%之后,应变剧增直至破坏。 相似文献
6.
薄片漏斗试样的应变等效换算与Zr-4合金疲劳寿命估算 总被引：1，自引：0，他引：1
完成了Zr-4合金薄片漏斗小试样的横向等幅应变疲劳试验;提出了薄片漏斗试样细腰部与薄片等直试样疲劳损伤等效的局部损伤等效假设;基于弹塑性有限元分析,建立了Zr-4合金薄片漏斗小试样横向测试应变向轴向应变转换的应变等效转换模型,该模型考虑了几何效应和泊松效应;结合实验结果,提出了用于Zr-4合金应变疲劳寿命估算的Manson-Coffin(M-C)模型。研究表明:薄片漏斗小试样及其应变等效转换模型可以有效应用于薄片金属材料的低周疲劳试验和寿命估算;国标推荐的应变换算公式应用于薄片漏斗小试样的Zr-4合金疲劳寿命估算会带来很大安全余量。 相似文献
7.
RAHMAN M. M. ARIFFIN A. K. 《浙江大学学报(A卷英文版)》2006,7(3):352-360
INTRODUCTION Due to market pressures for improvements in productivity, reliability, ductility, wear resistance and profitability of mechanical systems, manufacturers are placing increasing demands on available materials.Economic constraints require that these materials are inexpensive and easily available. In order to enhance the surface properties of today’s materials, producers of components are turning to different surface finish and treatments. There are several techniques available … 相似文献
8.
Qiu Zhao Kongsheng Chen Meizhong Chen Bruno Briseghella Zhiyong Guo Guotao Yang 《天津大学学报(英文版)》2018,(5)
The blind-hole method is the most widely used approach to experimentally determine the distribution of residual stress. This paper aims to improve test accuracy of welding residual stress and conducts an experimental study on the strain release factors involved when using the blind-hole method for Q235 and Q345, two steels commonly used in building structures. The ranges of strain release factors A and B in the elastic stage, the effects of strain release factors on residual stress calculated values, and the plastic corrected strain release factors are analyzed considering of the effect of plastic deformation around the blind hole on measurement accuracy. Finally, a simplified calculation formula to determine strain release factors is proposed for use with the blind-hole method. Results show that in the elastic stage, strain release factor A for Q235 and Q345 ranges from-0.399 to-0.525 and strain release factor B from-0.791 to-0.960. Changing the strain release factors A and B shows that calculated residual tensile stress varies in relation to a decrease in both factor values. However, there is a increase in calculated residual compressive stress with a decrease in the strain release factor A value, but there is an decrease with a decrease in strain release factor B value. Calculated residual stress applied to elastic strain release factors is compared with that applied to amended plastic strain release factors for Q235 steel. The maximum deviation between calculated residual stress and test stress is reduced from 21.1 to 1.0%,and for Q345 steel from 26.5 to 1.2%. It is thus evident that the plastic correction formula proposed in this paper can be used in calculations when conducting a residual stress test. 相似文献
9.
为获得路用水泥混凝土在高应力比作用下其疲劳可靠度的变化规律,首先推导了包括混凝土疲劳寿命在内的单调随机变量的概率密度,然后推导了 Miner 与 Chaboche-Zhao 疲劳损伤模型的概率密度. 借助室内疲劳试验结果,获得这 2 种模型的疲劳损伤概率密度函数. 最后,将荷载作用次数代入上述函数,从而获得水泥混凝土疲劳可靠度随荷载作用次数的变化规律. 结果表明: 随着荷载作用次数的增加,相同应力比下,疲劳可靠度从 100%逐渐衰减为 0%; 无论何种应力比,在荷载作用初期,疲劳可靠度均有一个较为稳定的阶段; 随着应力比的增加,该稳定阶段逐渐缩短,且可靠度为 0%时对应的荷载作用次数也减小; 在可靠度衰减阶段,对于相同荷载作用次数,应力比越高,则混凝土可靠度越低; 此外,Miner 疲劳损伤模型比Chaboche-Zhao 疲劳损伤模型偏安全. 相似文献
10.
Fatigue tests were conducted on tapered plain concrete prism specimens under triaxial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2fc and the upper stress ranged from 0.20ft to 0.65ft. Three constant lateral pressures were 0.1fc, 0.2fc and 0.3fc respectively. Based on the results, the three-stage evolution nile of the fatigue stiffness, maximttm(minimum) longitudinal strain and damage were analyzed, and a unified S-N curve to calculate fatigue strength factors was worked out. The results show that the fatigue strength and fatigue life under triaxial constant-amplitude tension-compression cyclic loading are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing their relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures. 相似文献
11.
The aim of this research is to characterize the development of fatigue damage by means of stress-strain hysteresis. Experiments were conducted on 14 specimens made of cold-finished unannealed AISI 1018 steel. Results demonstrate that the mechanical hysteresis loop areas, when plotted as a function of the number of loading cycles, show significant variations and demonstrate the three principal stages concerning the progress of the fatigue failure--initial accommodation, accretion of damage and terminal failure. These three stages of fatigue are marked by the transitions at cycles N2 and N3. Experimental results show that although fatigue life Nf ranges from 2644 cycles to 108 992 cycles, the ratios of N2/Nf and N3/Nf tend to be stable： N2/Nf=I 0.7%, N3/Nf=91.3%. 相似文献
12.
Improving the Fatigue Performance of the Welded Joints of Ultra-Fine Grain Steel by Ultrasonic Peening 总被引：2，自引：0，他引：2
Contrast tests were carried out to study the fatigue performance of the butt joints treated by ultrasonic peening, aiming at the improvement of ultrasonic peening treatment(UPT) on welded joints of a new material. The material is a new generation of fine grain and high purity SS400 steel that has the same ingredients as the traditional low carbon steel. The specimens are in two different states:welded and ultrasonic peening conditions. The corresponding fatigue testing data were analyzed according to the regulation of the statistical method for fatigue life of the welded joints established by International Institute of Welding(IIW). Welding residual stress was considered in two different ways: the constant stress ratio R = 0.5 and the Ohta method. The nominalstress-number (σ-N) curves were corrected because of the different plate thickness compared to the standard and because there was no mismatch or angular deformation. The results indicated that: 1 ) Compared with the welded specimens, when the stress range was 200 MPa, the fatigue life of the SS400 steel specimens treated by ultrasonic peening is prolonged by over 58 times, and the fatigue strength FAT corresponding to 106 cycles is increased by about 66％; 2) As for the SS400 butt joint ( single side welding double sides molding) , after being treated by UPT, the nominal S-N curve (m = 10) of FAT 100 MPa(R =0.5) should be used for fatigue design. The standard S-N curves of FAT 100 MPa (R = 0.5, m = 10) could be used for fatigue design of the SS400 steel butt joints treated by ultrasonic peening. 相似文献
13.
通过对配置HRB600非预应力钢筋的预应力混凝土梁进行受弯试验,分析了混凝土及非预应力钢筋应变的发展规律,研究了预应力筋预应力损失的计算方法,提出了试验梁短期抗弯刚度的计算修正公式。研究结果表明:试验梁跨中截面平均应变符合平截面假定,HRB600钢筋的受力过程呈现显著的三阶段发展规律;计算预应力筋的预应力损失σ_4和σ_5时,引入时间影响系数可以有效提高准确性;通过引入综合配筋率影响系数,可以有效提升试验梁的短期刚度计算精度,配置HRB600非预应力钢筋的预应力混凝土梁在正常使用阶段满足挠度限值要求。 相似文献
14.
针对机采油井油管经常发生疲劳断裂的问题,加工了J55油管疲劳试件,通过成组多级疲劳试验法,获得了J55油管高周疲劳分组试验数据。通过疲劳寿命的参数估计和疲劳寿命的分布类型检验,获得了J55油管在不同轴向应力水平下的疲劳寿命、分布规律和P-S-N曲线。结果显示,J55油管的疲劳寿命服从对数状态分布,其S-N曲线服从一般金属的疲劳S-N曲线形式。在疲劳寿命一定时,欲获得较高的可靠性,需大幅度降低油管的疲劳应力。 相似文献
15.
FRP加固RC圆柱正截面受弯承载力计算（英文） 总被引：1，自引：0，他引：1
运用数值计算方法对FRP加固钢筋混凝土（RC）圆柱截面特性进行计算,发现截面破坏时受压区高度主要受轴压比、FRP约束强度比和纵筋配筋特征值3个主要参数影响.根据数值计算的结果进行回归,提出了受压区对应圆心角θ的计算方法.数值计算结果显示,横向约束导致的混凝土应力提高以及纵筋屈服后的强化效应使RC柱破坏时截面受弯承载力远大于规范规定值.根据理论分析和36个大比例试件实测结果提出截面破坏时受弯承载力计算方法,计算结果与试验结果吻合很好.最后,对一个典型柱变形能力进行参数分析,研究轴压比,纵筋配筋特征值和FRP约束强度比对正截面变弯承载力的影响.结果显示FRP加固圆柱破坏时受弯承载力可以比规范规定的未加固柱受弯承载力提高50%左右. 相似文献
16.
钢桥面硬沥青浇注式沥青混合料低温性能研究 总被引：6，自引：0，他引：6
通过汉堡轮辙试验 ,考察了浇注式沥青混合料的抗车辙能力 ,硬沥青浇注式沥青混合料具有良好的抗车辙能力 .通过低温弯曲试验和逐步降温的钢桥面铺装复合结构疲劳试验 ,测试与比较了使用硬沥青的浇注式混合料低温抗裂性能 .高性能聚合物改性沥青浇注式混合料具有较长的疲劳寿命和较低的断裂温度 ,可用于钢桥面浇注式沥青铺装 . 相似文献
17.
为了提高高速货运列车转向架弹簧的耐疲劳性能,对两个炉号的棒状60Si2CrVAT弹簧钢用相同工艺热处理后,在MTS880材料试验机上进行了三点弯曲疲劳寿命对比试验,实验载荷采用阶梯式增加法;用扫描电镜对弹簧钢的疲劳断口和基体组织进行观察。疲劳实验结果表明,不同炉号的弹簧钢疲劳寿命相差很大。组织分析表明,疲劳寿命较低的弹簧钢中,淬火加热前存在颗粒状碳化物,奥氏体化时未溶入奥氏体而残留在淬火组织中,并在局部聚集,导致疲劳寿命降低。 相似文献
18.
成磊 《晋城职业技术学院学报》2011,4(2):39-43
采用ANSYS有限元分析软件建立Au-Al引线键合模型考察键合区在热循环加载下的应力应变情况;并采用Coffin-Manson方程计算了在热循环加载下焊点的疲劳寿命。结果表明：随着热加载循环次数的增加,模型的应力应变将增大;施加约束后,模型的应力将减小,引线键合的寿命延长。此方法可以比较各种不同情形下Au-Al引线键合热可靠性。 相似文献
19.
钢桥面铺装体系等效轴载换算方法 总被引：2，自引：0，他引：2
通过对钢桥面铺装主要病害的研究与分类,提出了桥面铺装结构设计的指标参数体系,并应用疲劳等效的原理,推导了轴载等效换算公式.根据室内试验和理论分析,分别研究了3种典型的铺装结构对应3种不同轴载类型的受力特性,并提出了各自轴载换算公式的参数的取值.3种轴载类型包括:单轴单轮组、单轴双轮组、双轴双轮组.通过对桥面铺装的影响因素包括气候与环境、交通、受力状态等使用条件的分析,提出的轴载等效换算公式与参数取值经过现场测试数据进行修正后,可以应用于新建桥梁桥面铺装的设计和已建桥梁桥面铺装使用状况的评价. 相似文献
20.
Extensive research has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminates are particularly suitable for improving the fatigue behavior of reinforced concrete (RC) beams. This paper presents the research on flexural rigidity evolvement laws by testing 14 simple-supported RC beams strengthened with carbon fiber laminates (CFL) under cyclic load, and 2 under monotone load as a reference. The cyclic load tests revealed the peak load applied onto the surface of a supported RC beam strengthened with CFL is linear to the logarithm of its fatigue life, and the flexural rigidity evolvement undergoes three distinct phases: a rapid decrease from the start to about 5% of the fatigue life; an even development from 5% to about 99% of the fatigue life; and a succedent rapid decrease to failure. When the ratio of fatigue cycles to the fatigue life is within 0.05 to 0.99, the flexural rigidity varies linearly with the ratio. The peak load does not affect the flexural rigidity evolvement if it is not high enough to make the main reinforcements yield. The dependences of the flexural rigidity of specimens formed in the same group upon their fatigue cycles normalized by fatigue life are almost coincident. This implies the flexural rigidity may be a material parameter independent of the stress level. These relationships of flexural rigidity to fatigue cycles, and fatigue life may be able to provide some hints for fatigue design and fatigue life evaluation of RC member strengthened with CFL; nevertheless the findings still need verifying by more experiments. 相似文献