Interdependence of Distortion and Residual Stress Relaxation of Cold-Rolled Bearing Rings During Heating

This article discusses the distortion behavior during heating of bearing rings produced by cold rolling. The residual stress relaxation was characterized intensively and correlated to the distortion behavior. In the initial state, the rings show compressive residual stresses in tangential and axial direction with almost no variations along the circumference. Because of the cold-rolling process, the entire cross section is affected by residual stresses. The rings present a characteristic size change between the soaking temperatures 773 K and 823 K (500 °C and 550 °C), which can be correlated with the macroresidual stress relaxation in the core of the rings. Changes in roundness deviation were found, but the amplitude of oval and triangular shape increases continuously until austenitizing temperature is reached. As the macrostress relaxation is already completed at 873 K (600 °C), another mechanism should be responsible for these distortions. A correlation between amplitude of the oval shape and decrease of full width at half maximum seems to be present. This may indicate that inhomogeneous recrystallization happens along the circumference of the rings. A triangular shape may result from the influence of the loading tool used as rings are positioned on three contact points during the stress relief treatment.     

Evaluation of Strain Hardening During Uniaxial Tensile Loading Followed by Stress Relaxation and Reloading

Metallurgical and Materials Transactions A - The estimation of strain hardening during uniaxial tensile loading followed by stress relaxation and reloading is required to quantify the strain aging...     

多轴非对称循环下材料的循环特性

在不同应变比下,按照总应变控制等幅循环阶梯加载方式,测定了材料在拉-压、拉-拉及扭转循环下相应的循环载荷-变形曲线,得出了材料的循环应力及应力比随应变比的变化关系。     

The Effect of Aging on the Relaxation of Residual Stress in Cast Aluminum

Most cast aluminum-engineered components are water quenched after the solution-treatment cycle of the casting process. This rapid water quenching has the potential to induce high residual stresses in regions of the castings. Reducing the amount of residual stress can have a promising effect on the life of the component. This study was conducted to quantify how aging affects the amount of residual stress in an aluminum casting. An engineered high residual stress test sample and quenching technique has been developed, and a relaxation study has been completed. The study focused on four different temperatures: 463 K, 493 K, 513 K, and 533 K (190 °C, 220 °C, 240 °C, and 260 °C) and a range of aging times (0.3 to 336 hours). The aging data were used to verify a stress relaxation model. The results indicated that as the aging temperature increased, the amount of relaxation of the residual stress increased.     

Behavior of Railroad Ballast under Monotonic and Cyclic Loading

A relatively new method for mechanized maintenance of railroad ballast (stoneblowing) puts a layer of single size stone between the ballast and each tie creating a two-layer gravel support. To get a better understanding of the behavior of this arrangement series of large diameter, triaxial tests have been carried out on single size and layered specimens. A new method of quantifying particle breakage during testing has been developed, and a conceptual model used to explain the combined effects of shearing and breakage on observed specimen behavior.     

局部加载拉应力对圆柱薄壳焊接残余应力场分布的影响

采用有限元模拟技术,从理论上论证了通过局部加载减小焊接残余应力技术路线的可行性.比较了焊接过程中拉伸与焊后拉伸降低应力在机理上的不同,研究表明,焊接过程中拉伸远比焊后拉伸效果好.200 MPa外力拉伸时,焊后拉伸残余应力最大值由常规焊条件下的235 MPa降至90 MPa左右,焊接过程中拉伸残余应力最大值可降至30 MPa左右.     

Residual Performance of FRP-Retrofitted RC Columns after Being Subjected to Cyclic Loading Damage

Numerous recent research findings evidenced the success of retrofitting existing RC columns using fiber-reinforced plastic (FRP) jacketing. However, little is known about the residual performance of FRP-retrofitted RC columns following limited seismic damage. In this paper, the residual performance of FRP-retrofitted columns damaged after simulated seismic loading is studied. Eight model columns with a shear aspect ratio of 5.0 were tested first under cyclic lateral force and a constant axial load equal to 20% of the column gross axial load capacity. The main parameters considered were the type of FRP jacket and peak drift ratio where the lateral loading was interrupted. Glass fiber-reinforced plastic (GFRP) and carbon fiber-reinforced plastic (CFRP) were both used for retrofitting. Five of the model columns were subjected to long-term axial loading after being subjected to limited damage by lateral cyclic loading. From the results of long-term loading test, it was found that FRP-retrofitted columns had much smaller creep deformation than the counterpart as-built model. The deformation of retrofitted columns under long-term axial loading depended on the previous damage intensity and the modulus of elasticity of FRP. The effective creep Poisson’s ratios of the retrofitted columns were much smaller than the as-built column but identical for GFRP and CFRP retrofitted columns. Under the testing conditions of this study, the long-term axial deformation of retrofitted columns tends to be sufficiently stable, despite the simulated earthquake damage.     

Stress Deformation and Fluid Pressure of Bone Specimens under Cyclic Loading

Cyclic loading has been known to induce fluid flow and thus mechanotransduction in bones. In the past, four-point bending tests have been used exclusively in studying fluid flow in bones. In order to better understand the mechanism of deformation and fluid flow under loading, compression tests were done on trabecular bone specimens under drained and undrained conditions. In the drained tests, the volume change was observed, whereas in the undrained tests, excess pore fluid pressure was measured. Cyclic loading tests were conducted in addition to monotonic loading tests to observe the permanent volume change or excess pore fluid pressure with loading cycles. A fast loading rate gave a sharp rise in the excess fluid pressure compared to a slow loading rate. The strength and stiffness of the specimens appeared to deteriorate with an increased speed of loadings, but there was no appreciable difference between the results obtained from drained and undrained tests. The drained and undrained tests as described allowed a better understanding of bone behavior under loadings for a coupled stress-flow analysis.     

Experimental and Numerical Study of Railway Ballast Behavior under Cyclic Loading

This paper presents the results of the influence of frequency on the permanent deformation and degradation behavior of ballast during cyclic loading. The behavior of ballast under numerous cycles was investigated through a series of large-scale cyclic triaxial tests. The tests were conducted at frequencies ranging from 10–40 Hz, which is equivalent to a train traveling from 73 km/h to 291 km/h over standard gauge tracks in Australia. The results showed that permanent deformation and degradation of ballast increased with the frequency of loading and number of cycles. Much of breakage occurs during the initial cycle; however, there exists a frequency zone of 20?Hz ? f ? 30?Hz where cyclic densification takes place without much additional breakage. An empirical relationship among axial strain, frequency and number of cycles has been proposed based on the experimental data. In addition, discrete-element method (DEM) simulations were carried out using PFC2D on an assembly of irregular shaped particles. A novel approach was used to model a two-dimensional (2D) projection of real ballast particles. Clusters of bonded circular particles were used to model a 2D projection of angular ballast particles. Degradation of the bonds within a cluster was considered to represent particle breakage. The results of DEM simulations captured the ballast behavior under cyclic loading in accordance with the experimental observations. Moreover, the evolution of micromechanical parameters such as a distribution of the contact force and bond force developed during cyclic loading was presented to explain the mechanism of particle breakage. It has been revealed that particle breakage is mainly due to the tensile stress developed during cyclic loading and is located mainly in the direction of the movement of ballast particles.     

In-Situ TEM Observation of Twinning and Detwinning During Cyclic Loading in Mg

In-situ transmission electron microscopy (TEM) is used to directly observe twin evolution in Mg under tension and compression. Twins grow during tensile loading. Upon load reversal, the first-generation twin detwins by nucleation and growth of a second-generation twin within its volume. This mechanism for detwinning is different from the more traditional mechanism of detwinning by reverse motion of a twin boundary. Reloading in tension causes the second-generation twin to recede, leaving behind residual features. In compression, the second-generation twin re-nucleates in the area of this debris, and grows. Interactions between dislocations and twin boundaries change the character of the observed dislocations. Direct observation of such behavior aids in clearer understanding of the observed microstructures from post-mortem TEM.     

TC4合金应力松弛行为及微观组织观察

钛合金因其高的比强度和耐腐蚀性而在航空、航天、化工等各个领域受到人们的青睐 ,受到广泛的应用[1～ 3 ] 。钛合金的重要的力学性能之一为应力松弛性能。应力松弛是热校形的理论基础[4 ] ,同时也是消除应力退火的理论基础[5] 。另一方面 ,有许多弹性元件为了减轻本身的重量而采用比强度高的钛合金进行制造 ,应力松弛往往是这些元件失效的原因 ;在一些先进的飞机上 ,钛合金紧固件被广泛采用 ,应力松弛往往导致一些事故。要有效地防止因应力松弛导致钛合金弹性件和紧固件失效 ,就要了解钛合金应力松弛机理。基于以上两方面的应用背景 ,研究…     

Behavior of a Semiintegral Bridge Abutment under Static and Temperature-Induced Cyclic Loading

This paper presents the results of an experimental study of semiintegral bridge abutments. Primary interests were to investigate (1) potential problems with the particular detail tested; (2) rotational characteristics of the semiintegral abutments; and (3) ability of the specimens to withstand cyclic loading induced by temperature variations during the expected life of the bridge. Sixteen experiments were conducted on three large-scale specimens. The results of the tests have shown that semiintegral abutments can significantly reduce the moments transferred from the superstructure to the foundation piles. Test results have also shown that semiintegral abutments can tolerate the number of displacement cycles that a bridge will experience during the course of its economic life.     

Texture Evolution and Residual Stress Relaxation in a Cold-Rolled Al-Mg-Si-Cu Alloy Using Vibratory Stress Relief Technique

Over the last half century, vibratory stress relief (VSR) has come to be recognized as a technique with several unique benefits, and it has found applications in various industries. However, the mechanisms involved remain unclear, and the textures corresponding to residual stress relaxation were rarely reported in the existing literature. The purpose of this study is to discuss the texture evolution and residual stress relaxation in a cold-rolled Al-Mg-Si-Cu alloy using VSR technique. All the residual stress measurements were performed using a standard X-ray diffraction (XRD) technique. Measurement of texture was performed on the specimen surface using conventional pole figure (PF) as well as orientation distribution functions (ODFs) methods. Results indicate that the VSR technique can be applied to weaken the α-fiber and cause the residual stress of the rolled samples to gradually approach uniformity in XRD analysis. The best relaxation of the compressive residual stress reaches about 52.6 pct, but relaxation of the tensile residual stress is less than 10 pct. After the VSR process for 20 minutes, the texture intensities of PFs (200) and (220) as compared to those in nonvibration are nearly homogeneously distributed. Furthermore, the texture of (111) PF perpendicular to normal direction (ND), which is affected by vibratory force parallel to ND, almost disappears.     

Effect of Solute Clusters on Stress Relaxation Behavior in Cu-Ni-P Alloys

In this study, the ultrafine structures in Cu-P and Cu-Ni-P alloys have been characterized using a three-dimensional atom probe (3DAP) and transmission electron microscopy (TEM), and the stress relaxation behavior of these alloys has been explored. The results show that low-temperature annealing greatly improved the stress relaxation performance, especially in the Cu-Ni-P alloys. The presence of Ni-P clusters in the Cu-Ni-P alloys has been revealed. The overall improvement in properties has been analyzed in terms of variations in the dislocation density and solute atom cluster density within these materials. It is shown that clusters with small average spacing give rise to significant improvements in the stress relaxation performance, without requiring significant change in the dislocation density.     

Bond Behavior of Near-Surface Mounted CFRP Laminate Strips under Monotonic and Cyclic Loading

Near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminate strips are used to increase the load-carrying capacity of concrete structures. This is done by inserting the CFRP strips into slits made in the concrete cover of the elements to be strengthened and gluing the strips to the concrete with an epoxy adhesive. In several cases the NSM technique has substantial advantages when compared with externally bonded laminates. To assess the bond behavior between the CFRP and concrete under monotonic and cyclic loading, an experimental program was carried out based on a series of pullout-bending tests. The influence of the bond length and loading history on the bond behavior was investigated. In this work the details of the tests are described and the obtained results discussed. Using the experimental data and an analytical-numerical strategy, a local bond stress-slip relationship was determined. A finite-element analysis was performed to evaluate the influence of the adhesive on the global response observed in the pullout-bending tests.     

Microscopically-Determined Static Recrystallization of Copper During Holding Without Stress or with Stress Relaxation After Hot Working

Abstract

After deformation to 0.15 in the range 450–540°C and 1.8 × 10^?3 to 1.8 s^?l in compression or torsion, the recrystallization of ETP Cu determined microscopically is compared to the restoration measured mechanically during intervals of holding at the deformation temperature under both stress-free and stress-relaxation conditions. Recrystallization is initially much slower than softening, the difference being due to recovery, but finally they become equal at about 85%. TEM substructures sharpen considerably during intervals up to 100 s. Recovery and recrystallization occur more rapidly as strain rate and temperature rise in both modes of holding, but in stress relaxation the former is slowed down and as a result the latter is speeded up.     

Effects of Loading Frequency on Fatigue Behavior,Residual Stress,and Microstructure of Deep-Rolled Stainless Steel AISI 304 at Elevated Temperatures

Metallurgical and Materials Transactions A - The effects of loading frequency on the fatigue behavior of non-deep-rolled (NDR) and deep-rolled (DR) austenitic stainless steel AISI 304 were...     

Combined Shear and Flexural Behavior of Hybrid FRP-Concrete Beams Previously Subjected to Cyclic Loading

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) were initially proposed for bridge substructures in corrosive environments in the early 1990s. Systematic studies have since demonstrated the feasibility and merits of CFFTs with or without internal mild steel reinforcement. However, the experimental database in this field is still quite limited. This paper enhances the test database through a series of monotonic bending tests on one control RC specimen and five CFFT specimens previously subjected to reverse cyclic loading. Although the control RC specimen suffered shear-flexural cracks, specimens with carbon fibers experienced flexural failure by longitudinal splitting of the FRP tube in tension and its crumpling in compression. Specimens with glass or hybrid (glass/carbon) fibers, on the other hand, all failed by local buckling of FRP with either burst crushing or crumpling cracks. The specimen with hybrid fibers had higher normalized initial stiffness primarily because of its higher FRP/concrete stiffness ratio. The tests showed that the ductility of CFFT increases with FRP rupture strain. Further synthesis of flexural strength with FRP and mild steel reinforcement indexes reveals the existence of an optimized overall reinforcement index to achieve a design moment without overconfining concrete. Finally, the study confirms that shear failure is not critical for CFFT specimens at short shear span-to-depth ratios, even with internal mild steel reinforcement, as long as the FRP architecture is designed properly.