Papers by Keyword: Stress Relaxation

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Authors: Lu Yu Zhou, Xian Bo Li
Abstract: In order to analyze the creep properties of UHMWPE multifilament and aramid multifilament, four-element model and Matlab software were used to get creep fitting curve, the corresponding mechanical fitting equation and microscopic parameters. The creep properties of the two kinds of multifilament were discussed by microscopic parameters. At the same time, the tensile and relaxation performance of UHMWPE multifilament and aramid filament were studied. Compared with aramid multifilament, UHMWPE multifilament has higher strength, better elongation, lower creep resistance and obvious the phenomenon of stress relaxation. This article will provide some basic performance reference to the application of UHMWPE multifilament.
Authors: Taketo Sakuma, Zhang Lian Hong, Hidehiro Yoshida, Yuichi Ikuhara, Toshiyasu Nishimura, Mamoru Mitomo
Authors: Seung Min Hyun, Walter L. Brown, Richard P. Vinci
Abstract: Thin metal films often play an important role as structural elements or reflective surfaces in MEMS applications. Mechanical properties of the films are important due to their influence on the performance of MEMS devices that involve bending or stretching metal parts. In order to gain a better understanding of the mechanical behavior of thin metal films, we have developed a novel bulge system and measured mechanical properties of aluminum thin films. The thin films were prepared by e-beam evaporation of high purity Al onto 2 or 3mm ×12 mm rectangular silicon nitride membrane windows in silicon frames. N2 gas was used to pressurize and thus bulge the membranes. The bulge height was measured based on changes of capacitance between the membrane and a fixed, closely spaced electrode. This apparatus provides resolution of approximately 50 nm in bulge height at a data acquisition rate of 100/sec and provides strain rates in the membrane up to 10-5/sec. The stability of the apparatus allows stress relaxation measurements to be made to times of many hours. Time dependent elastic modulus changes of 1 m Al films were measured over periods of times under constant stress.
Authors: Jun Jie Xiao, Dong Sheng Li, Xiao Qiang Li, Ming Jin Xu
Abstract: In order to reduce the energy consumption and working procedure for manufacturing thin-walled titanium alloy components, a hot stretch-creep forming (SCF) technique via resistance heating is proposed to form the hard-to-form material. Firstly, the principle of hot SCF was introduced that the technique can manufacture titanium alloy components precisely because the residual stress relaxes in the material during the dwelling time. Secondly, the hot SCF equipment via resistance heating was developed, which makes use of electrical current for heating the titanium materials to improve their ductility. Then based on a set of optimized process parameters, including forming temperature, stretch velocity, post stretch percentage and dwelling time, a comparative experment of single curvature Ti-6Al-4V alloy sheet components was conducted via this innovative technology to examine the hot SCF equipments and the effect of creep forming. Results show that the component precision of the hot SCF is more precise than that of the hot stretch forming (SF) due to the creep in the stress relaxation period. Comparing to the as-received material, the yield strength of the material suffered hot SF decreases a little; while the strength suffered hot SCF increases a little. This novel technique shows a promising future to manufacture titanium sheet or profile components precisely as a feasible and cost-effective way.
Authors: Mahesh C. Somani, L. Pentti Karjalainen
Abstract: In recent past, a linear regression model to predict the activation energy (Qrex) and kinetics of static recrystallisation for hot-deformed austenite was developed based on stress relaxation test results of over 40 different carbon steels. The model is able to predict satisfactorily the static recrystallisation (SRX) kinetics of common carbon steel grades (including microalloyed steels) and also several special steel grades. In this study, the main effects of seven alloying elements, viz., C, Mn, Cr, Ni, Mo, Nb and V, on the activation energy of recrystallisation were further examined by using eight experimental steels based on an orthogonal Taguchi L8 matrix. All steels contained constant additions of B, Ti and Si. Even though originally intended for studies on phase transformation characteristics and hardenability under direct quenching conditions, the L8 matrix steels were suitably employed for further validation of the SRX regression model. In addition, the SRX characteristics and kinetics of a set of new steel compositions including C-Mn, C-Mn-Nb and C-Mn-Nb-Ti types were examined in the light of model equations, which further confirm the suitability of the regression model.
Authors: Ji Ho Lim, Ji Soon Kim, Kyoung Wook Paik, Y.Y. Earmme
Authors: Yannick Champion, Sophie Nowak
Abstract: Fine grained copper was studied using the stress relaxation technique and creep testing in nano-indentation, to determine the activation volume involved in the micro-mechanism of the deformation. This material exhibits a near-perfect elasto-plastic deformation, featured by a steep work-hardening, after the elastic domain, followed by flow at a constant stress. Measurements of the activation volumes in the various domains reveal the role of the dislocations and the variation in the dislocation density in the deformation mechanism. This emphasizes the importance, in the determination of the activation volume, of the deformation domain investigated as well as the testing technique used and whether in both cases, the measurement is carried out in a transient domain or condition where variation in dislocation density occurs.
Authors: Jung Jun Park, Doo Yeol Yoo, Sung Wook Kim, Young Soo Yoon
Abstract: Since ultra-high performance concrete (UHPC) is subject to large occurrence of shrinkage at early age due to its low water-to-cement ratio, the mixing of large quantities of powdered admixtures and the absence of coarse aggregates, UHPC presents large risks of shrinkage cracking caused by the restraints provided by the form and reinforcing bars. Accordingly, this study intends to evaluate the shrinkage behavior of UHPC under restrained state by performing restrained shrinkage test using ring-test. The test results reveal that increasing thickness of the inner ring increases the tensile creep at early age leading to the reduction of the average strain and residual stress of the inner ring.
Authors: Ying Xiong
Abstract: In this paper, fatigue test and numerical simulation are carried out for Q345 weld joint under constant amplitude loading at different R-ratio using the compact tension samples with 3.8mm thickness. The result indicates that fatigue crack growth rates in the base metal is not sensitive to R-ratio, but the fatigue crack growth rates increases in the weld zone with R-ratio increasing. The effect of R-ratio on fatigue crack growth is analyzed based on J-S cycle plasticity model and Jiang’s multiaxial fatigue criterion. The finite element method (FEM) is used for the stress-strain analysis with the implementation of an accurate J-S cyclic plasticity model. With the detailed stresses and strains, fatigue damage assessment is made using a Jiang’s multiaxial fatigue criterion.
Authors: Xiao Hong Yuan, Ying Jin Gan, Dong Sheng Chen, Yuan Jing Ye
Abstract: To understand the fundamental mechanical properties of lotus fiber could provide theoretical basis for developing lotus fiber fabric. This paper is focused on the mechanical properties of lotus fiber under the state of wet, dry and normal temperature, which include the single tensile properties, the repeated tensile stress properties under constant elongation, stress relaxation and creep properties, and have comparation and analysis on the cotton fiber and the viscose fiber. The conclusion shows that the lotus fiber and viscose fiber are more effect by humidity than the cotton fiber. The fibre strength of lotus fiber was the biggest than cotton fiber and viscose fiber under the normal temperature and dry state. The elongation at break of viscose fiber was the biggest than lotus fiber and cotton fiber under the state of wet, dry and normal temperature. From wet state to normal temperature state to dry state, the fiber strength of lotus fiber increase gradually, and elongation at break gradually decreased. The plastic deformation resistance ability, the stress relaxation and creep properties of bamboo pulp fiber under wet state are best, and the dry condition are the worst.
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