Papers by Keyword: Cyclic Plasticity

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Authors: Kyriakos I. Kourousis
Abstract: Advanced light metals have recently attracted the interest of the aerospace and automotive industry. The need for accurate description of their cyclic inelastic response under various loading histories becomes increasingly important. Cyclic mean stress relaxation and ratcheting are two of the phenomena under investigation. A combined kinematic isotropic hardening model is implemented for the simulation of the behavior of Aluminum and Titanium alloys in uniaxial mean stress relaxation and ratcheting. The obtained results indicate that the model can perform well in these cases. This preliminary analysis provides useful insight for the evaluation of the models capabilities.
Authors: Yan Luo
Abstract: Based on the characteristic of cyclic softening of the quenched and tempered Carbon steel 45, a cyclic plastic constitutive model was proposed to describe the cyclic behavior under symmetrical and unsymmetrical strain cycling with different strain amplitudes. In this model, the phenomenon of the decrease of the up yield limit stress with the increase of strain in the initial 1/4 cycle was taken into account. The proposed evolution equations of the yield size and backstress can simulate the cycling softening under symmetrical and unsymmetrical strain cycling well. The results indicated that either the simulated shape of the cyclic softening hysteresis loops or the evolution of stress amplitude with the increase of the cyclic number during the low cycle fatigue coincides with the experimental ones very well.
Authors: Jiri Protivinsky, Martin Krejsa
Abstract: Aseismic design of modern structures imposes a new requirement on structural engineers. Structural systems should withstand even very huge earthquakes. This goal cannot be achieved by standard design methods applying a linear elastic approach. An advanced aseismic design applies energy dissipating anti-seismic devices. During seismic event, these devices are exposed to a large plastic strain. The code EN 15129 is the standard on anti-seismic devices applicable in Europe. Mentioned standard defines a special material requirement imposed on devices working as energy absorbers. Material verification is possible only experimentally. In compliance with the instructions contained in the code EN15129, several cyclic tests of the materials S235 and DD11 have been used. Evaluation of the previous research and the current test results have proved that structural steel S235 is not applicable to the anti-seismic devices. As an alternative, steel DD11 has been suggested for this application. The test results have shown that the steel DD11 is applicable in specified range of target strain amplitudes.
Authors: Mouaad Brik, Malek Chabane Chaouche, Lakhdar Taleb
Abstract: The study presented in this paper uses a multi-mechanism model (MM) in order to simulate the cyclic behavior of an anisotropic aluminum alloy 2017A subjected to complex loading. Two sets of parameters were used. The first set is proposed in [1]; it is identified considering cyclic tests performed under strain control following proportional and non-proportional paths. The second set of parameters has been identified recently on a larger database [2]. In this work, we propose to evaluate the capability of the according to the set of parameters under consideration. Note that the identification process in both cases was performed using strain controlled experiments while the evaluation of the model uses stress controlled experiments.
Authors: Aaron Alejandro Aguilar Espinosa, Neil Fellows, Oscar Portillo
Abstract: The numerical simulation of crack closure is employed to assist on the prediction of crack growth rate. Under fatigue load, the stress-strain response of metals is altered due to cyclic loading. For this reason, the material properties characterization is of prime concern as an input parameter to obtain reliable results. From numerical simulations, it was observed that simple material models do not provide accurate data for long crack lengths. In this paper, the effect that different hardening models have on the opening response of a cracked component when it is subject to variable amplitude loading is analyzed. The interaction effects (crack arrest/acceleration) for long crack length simulation are specially highlighted. For this purpose, a 6082-T6 aluminium alloy was analyzed experimentally and numerically in order to measure crack closure, and then, those data were used to predict fatigue crack growth rate under different patterns of overload. The Paris equation and the Elber crack closure concept were employed. The results showed that small variations in the opening stresses obtained from different material models produce high overestimated simulations of crack growth rate. Also, it was proved that the crack closure mechanism is able to take into account interaction effects due to variable amplitude loading.
Authors: Yusuke Tomizawa, Takehito Suzuki, Katsuhiko Sasaki, Ken-Ichi Ohguchi, Daisuke Echizenya
Abstract: Recently, Halt (Highly accelerated limit test) is widely employed for evaluation of reliability of electronic products. Halt condition is quite severe. The tested products are subjected to mechanical impacts, thermal shock, and vibration at same time. However, there has not been a reasonable and accurate evaluation method for Halt yet. To construct an accurate evaluation method of Halt, basic deformation mechanism of parts of the electronic products should be clarified from both experimental and theoretical points of view. In this paper, focusing on solder joints of circuit boards of electronic products, ratchetting deformation, especially, biaxial ratchetting deformation of solder joints is revealed from both experimentally and theoretically. The authors have already conducted biaxial ratchetting test combining axial and torsional cyclic loading using a tubular specimen of Type 304 stainless steel. However, as for solders, it is difficult to make tubular specimen. Since size of the solder joints is micron, a small size joint specimen of copper tube and solder is employed in this paper. First, to confirm the quality of the joint specimen such as boundary between copper and solder, both the tensile and cyclic loading tests are conducted at several temperatures using Sn-3Ag-0.5Cu. The basic characteristic of tensile and fatigue failure is obtained from these tests. After the confirmation of the accuracy of the joint specimen, biaxial ratchetting tests are conducted superposing the tensile load on cyclic torsion. The biaxial ratchetting tests are conducted using a biaxial loading testing machine developed for the joint specimens of solder and copper.
Authors: Justus Medgenberg, Thomas Ummenhofer
Abstract: The paper presents background information and experimental results regarding the assessment of fatigue damage in welded steel structures by thermographic investigations of thermomechanical coupling effects. The results confirm the high potential of specialized thermographic methods for the experimental characterization of all stages of fatigue damage in welded and un-welded components. The technique provides a new experimental mean to investigate early inhomogeneous fatigue damage as mesoplasticity and cracks in the weld toe. The method has been successfully applied during fatigue testing of welded components and allows detecting localized damage as early as 10% to 20% of the total fatigue lifetime of the tested specimens.
Authors: Masafumi Akamatsu, Nobutada Ohno, H. Takahashi, Takashi Kawakami
Authors: Seyed Behzad Behravesh, Hamid Jahed, Steve B. Lambert, Mi Chengji
Abstract: Fatigue testing was conducted on AZ31B-H24 magnesium alloy in strain-control condition. An unusual asymmetric shape of the hysteresis loop was the key feature of the cyclic behavior. A continuum-based cyclic plasticity model was developed to follow the asymmetric hardening behavior of wrought magnesium alloys. The proposed model was implemented in a UMAT subroutine to run with Abaqus/Standard. It was demonstrated that the UMAT was able to follow the cyclic hardening behavior of AZ31B under uniaxial loading. An energy-based damage parameter was proposed for estimating the fatigue crack initiation life. The developed UMAT along with the proposed damage parameter were used for fatigue modeling of an automotive substructure made of magnesium. It was shown that the proposed asymmetric model was more promising than a symmetric model.
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