Advanced Materials Research Vols. 291-294

Abstract: In order to test whether there is the change of mechanics performance cleaned by ultrasonic and deruster, the experiments on mechanics performance and sensitivity of hydrogen embrittlement have been conducted. During the experiments, 20Cr₂Ni₄A steel are selected as the materials, which endure the relatively great concussion load in the bad condition, and the gaps’ long-time permanence experiments and short-time tension and concussion experiments have been done. Through the compare of mechanics performances and the SEM analysis of tensile fracture surface of the samples, it can be proved that the mechanics performances and rupture mechanism are the same, no matter whether the materials are cleaned by ultrasonic and deruster or not. These indicate that it doesn’t bring the change of mechanics performances and hydrogen embrittlement to clean the materialss by ultrasonic and deruster.

Abstract: A series of parametric tests have been conducted to investigate the effect of curing period and cement content of the specimen on fracture energy of cement stabilized aggregate. By means of three-point bending method, the fracture energy of cement stabilized aggregate was measured. Four specimen curing periods (14 d, 28 d, 60 d and 90 d) and four different cement contents (4%, 5%, 6% and 7%) were used. The results indicate that the fracture energy of cement stabilized aggregate is increasing with the increase of specimen curing period. Besides, with the increase of cement content, there is a tendency to decrease in the fracture energy of cement stabilized aggregate. The ability of cement stabilized aggregate to resist crack propagation becomes weaker and weaker with the increase of cement content.

Abstract: The mechanics properties and fracture behaviors of 6061 aluminum alloy were investigated by the tensile shear tests and in-situ tensile shear tests with tensile shear specimen devised. The results indicate that a lot of slip bands parallel to tensile direction are produced on specimens’ surfaces. With shear strain rates increasing, the shear yield stress and shear ultimate stress of 6061 aluminum alloy remain constant basically, but the shear fracture strain decreased obviously. The grain boundaries of 6061 aluminum alloy are the weakest area and microcracks initiate at the grain boundaries parallel to tensile direction under shear stress. With shear stress increasing, the microcracks extend and coalesce. The fracture of specimens is due to coalescence or shearing between the microcracks.

Abstract: Pier concrete is vulnerable to cracking when using concrete rapid construction after long off period. In order to solve this problem, crack mechanism and effects of several temperature control measures of thin-walled structure concrete is analyzed. Through analyzing the temperature and stress time-space variation using 3D finite element method, it can be found that stress is more sensitive to controlling concrete placing temperature than other measures. It also shows that under the condition of taking other proper temperature control measures, low placing temperature can not be spared.

Abstract: In this paper, a new constitutive model for anisotropic material with isotropic damage is proposed by extending the Rousselier’s model. In this new model, the damage of anisotropic material is treated as a scalar and the Hill 1948 yield function is employed. A full-implicit integration algorithm which can be used in the finite element (FE) simulation is developed. The integration formula is coded into FE model by Abaqus/Explicit using User Material Subroutine and the fracture process is simulated by element deletion. The tensile tests of sheet metal of two different materials, 08 boiling steel and 1Cr18Ni9Ti, are taken under 3 directions. By simulations for specimen under tension, the evolutions of the damage variable are obtained. By comparing the load-displacement curve of the experiments with the simulation results, the validation of this model is verified.

Abstract: The second generation wavelet transform has shown the property of high flexibility in multiresolution analysis. Based on this powerful tool, a new finite element multiresolution method is proposed. By using this method, the equation can be resolved in the low-resolution space, and then the coarse solution can be refined by adding the detail solutions in the detail spaces gradually till the solution in a high-resolution space satisfies the expected accuracy. This method is easy to achieve self-adapting algorithm and is suited for solving the singular problems. Numerical tests demonstrate the validity of this method.

Abstract: Along with social progress, people pay attention to health. Modern people choose the gym to maintain posture and body functions well, therefore, the gym popularize everywhere. Popularity of expensive fitness equipment to bring a lot of convenience, but different users share of fitness equipment have different condition, often caused damage by use, which is the most important factor for the material fatigue damage. This study chose the exercise bike parts “self run bushing” to create a fatigue life assessment mechanism. In this study, to the fatigue analysis was conducted, by using finite element analysis according to the material S-N curve and Miner cumulative damage theory in a series of cyclic loading. To analyze fatigue life, analytical and experimental studies through mutual verification were conducted which can obtain the expectation life period of the self run bushing. The load spectrum based on different user can also be considered in this study. Based on the design frequency from different users, after the study of distribution of reliability and failure, the most appropriate time-out and the best replacement time can be obtained.

Abstract: A theoretical model is developed to account for the effects of strain rate and temperature on the deformation behavior of ultrafine-grained fcc Cu. Three mechanisms, including dislocation slip, grain boundary diffusion, and grain boundary sliding are considered to contribute to the deformation response simultaneously. Numerical simulations show that the strain rate sensitivity increases with decreasing grain size and strain rate, and that the flow stress and tensile ductility increase with either increasing strain rate or decreasing deformation temperature.

Abstract: Cold roll forming thin strip products occupy a rather large proportion of novel cold bending manufacturing. Conventional roller straightening could not obtain perfect straightening effects when the thickness of strip less than 1mm. On the basis of continuous roller stretcher straightening theory, we developed an area saved, high efficient strip straightening facility. At the same time, punching is also requested during the cold roll forming of strips. High quality productions can be achieved at high speed through the roller punching system, so the device is adaptive for high efficiency cold roll forming production.

Abstract: This study provides an engineering application of a continuum damage model to analyze the ductile tearing of axial surface cracks in X80 pipelines. Compact tension experiments were conducted to examine the behavior of large crack extension of X80 pipeline steel. The test results were used to verify the optimized parameter set of the proposed damage model. In the numerical model, progressive damage was restricted within a predetermined fracture process zone (FPZ). The material’s damage behavior in FPZ was described in terms of the Gurson–Tvergaard-Needleman (GTN) micro-mechanical damage model. The measured load versus load line displacement curve of CT specimens was numerically predicted using the damage model developed. T* integral was calculated to determine the limiting crack size in X80 pipelines. The damage model was then used to analyze the axial subcritical crack extension. It can help Leak-Before-Break (LBB) assessment.