Fracture and Damage Mechanics V

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Authors: Young Woo Choi, Byeong Wook Noh, Jung Il Song, Sung In Bae
Abstract: The fatigue life of hexagon head and socket head bolts, attached to vehicle a wheel, is assessed and the estimation of the residual life of existing bolts in vehicle wheel is investigated. Fieldmeasured load histories were applied in this test. Tensile tests and fatigue tests were performed to evaluate the effect of tightening torque and to obtain the basic experimental data. Miner’s rule was used to predict the fatigue life of bolts. The results indicate the prediction of fatigue life of the bolts was in good agreement with the real life of vehicle wheel bolts in this test.
Authors: Jian Zhong Xia, Zhan You Luo, Wei Tang Wang, Wei Liu
Abstract: For strain-softening materials with different elastic modulus of tensile compression, two controlling parameters were introduced to take into account the different modulus and strainsoftening properties. By means of twin shear unified strength theory, unified solutions calculating stress and displacement fields of expansion of cylindrical cavity were derived. The effects caused by different elastic modulus in tensile and compression, different models and strain-softening rates on stress and displacement fields, development of plastic zone were analyzed. The results show the ultimate expansion pressure, stress and displacement fields and development of plastic zone vary with the changes of different elastic modular, different models and strain-softening properties.
Authors: Cheng Yi, Shi Zhao Shen, He Ping Xie, Chang Jun Wang
Abstract: Partially High Percentage Fiber Reinforced Concrete (PHPFRC) is a kind of cement composite in which fibers are concentrated with high volume fraction in the tension region of the component under bending. Therefore, PHPFRC possesses much higher load bearing capacity, rigidity, fatigue and fracture properties than conventional steel fiber reinforced concrete (SFRC) while its cost is similar to that of SFRC. In this paper, the fatigue test of PHPFRC is carried out to gain its flexural fatigue damage evolution rule. It is found from the test that, PHPFRC have long post-crack fatigue life and its fatigue damage is tough damage. Based on the continuum damage mechanics and fatigue behavior of the specimens, a fatigue damage variable D for PHPFRC is defined and the elementary form of damage evolution function is determined. For the specimens in which average fiber volume fraction are 1.2% and local fiber volume fraction are 10%, the function parameters and the damage threshold value are given according to the test results.
Authors: Yun Peng Jiang, Wan Lin Guo
Abstract: Based on the classic laminate theory, a progressive damage model has been incorporated into the composite structure analysis by using a commercial code, ABAQUS, via one of its user-defined subroutine, UGENS. The developed user subroutine can be applied to simulate fiber and matrix damage processes in the general composites structures. The responses of flat laminate subjected to static contact crush have been studied to verify the efficiency of the presented damage method. The predicted load-displacement relationships, damage distribution were obtained and compared with the corresponding experiments, and the results were found to be in good agreement.
Authors: Aleš Belšak, Jože Flašker
Abstract: A crack in the tooth root, which often leads to failure in gear unit operation, is the most undesirable damage caused to gear units. This article deals with fault analyses of gear units with real damages. Numerical simulations of real operating conditions have been used in relation to the formation of those damages. A laboratory test plant has been used and a possible damage can be identified by monitoring vibrations. The influences of defects of a single-stage gear unit upon the vibrations they produce are presented. Signal analysis has been performed also in concern to a non-stationary signal, using the Time Frequency Analysis tools. Typical spectrograms, which are the result of reactions to damages, are a very reliable indication of the presence of damages.
Authors: Jae Hoon Kim, Duck Hoi Kim, Young Shin Lee, Gi Gwang Kim
Abstract: This paper presented the results for experimental investigations and numerical analysis performed with the aim of studying on fatigue life of hobbed and cold forged bevel gears used in automobiles. To evaluate the bending fatigue strength improvement by cold forging process, fatigue test and analysis were performed. For the monotonic fatigue loading, bending fatigue test and analysis were carried out. To simulate the real driving condition, random fatigue loading was defined here, and the random fatigue analysis was also performed. It was concluded that fatigue life and crack initiation sites of automotive bevel gear were well agreed with the test results. Fatigue lives for hobbed and cold forged bevel gear from experimental and analytical investigation were also presented and compared.
Authors: Sung Ryul Yun, Li Jie Zhao, Nian Gui Wang, Jae Hwan Kim
Abstract: Electro-Active Paper (EAPap) materials based on cellulose are attractive for many applications because of their low voltage operation, lightweight, dryness, low power consumption, bio-degradability. The construction of EAPap actuator has been achieved using the cellulose paper film coated with thin gold electrode layers. This actuator showed a reversible and reproducible bending movement. In order to improve both force and displacement of this, efforts are made to construct hybrid EAPap actuators using cellulose paper coated with carbon nanotubes (CNT). To coat the CNT, single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) are dispersed in polyaniline (PANI) matrix, and the solution is coated on the EAPap by using a spin coater. It is expected that the use of CNT can improve the force output by enhancing the stiffness of the hybrid EAPap actuator. Furthermore, the presence of the PANI may improve the actuation performance of the EAPap material. The performance of hybrid EAPap actuators is tested in an environmental chamber in terms of free displacement, blocked force and electrical power consumption. The performance of hybrid actuators is investigated for bio-mimetic applications.
Authors: Cedric Lequesne, A. Plumier, H. Degee, Anne Marie Habraken
Abstract: The fatigue behaviour of the welded beam-to-column connections of steel moment resisting frame in seismic area must be evaluated. The cohesive zone model is an efficient solution to study such connections by finite elements. It respects the energetic conservation and avoids numerical issues. A three-dimensional cohesive zone model element has been implemented in the home made finite element code Lagamine [1]. It is coupled with the fatigue continuum damage model of Lemaître and Chaboche [2]. The cohesive parameters are identified by the inverse method applied on a three points bending test modelling.
Authors: Jin Hai Liu, Xiao Yan Hao, Guo Lu Li, Xue Bo Zhao, Gen Sheng Liu
Abstract: The influence of fatigue ratio on the low cycle fatigue damage of nodular cast iron was investigated by measuring the elastic modulus. The results indicated that the elastic modulus of nodular cast iron is a sensitive parameter to the fatigue damage at low cycle. The fatigue damage variable of nodular cast iron increases with cycle ratio. At the beginning and end period of cycling, the damage of nodular iron increases sharply, and in the range of 0.2- 0.8 cycle ratio, the fatigue damage grows gradually.
Authors: Q. Wang, X. F. Sun, Kimihiro Ozaki
Abstract: In this paper, the strength of the singular stress field near the ends of the CNTs in composites was analyzed to clarify the effects of the CNT length on stress filed in the CNT reinforced composites when studying the fracture toughness. The singular stress field was separated into two types of singularities, symmetric and skew-symmetric, near the ends of CNTs according to the deformation and loading types. The stress intensity factors of the singular stress field were calculated for these two types of singularities. The effects of the CNT length in CNT reinforced composites on these stress intensity factors were investigated.

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