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Constant Amplitude Loading (constant + amplitude_loading)

Distribution by Scientific Domains

Polymers and Materials Science	80%

Selected Abstracts

Influences of the Process Chain on the Fatigue Behavior of Samples with Tension Screw Geometry,

ADVANCED ENGINEERING MATERIALS, Issue 4 2010
Marcus Klein
To analyze the influence of the material batch, the structure of the manufacturing process chain, and the process parameters, four different material batches of the quenched and tempered steel SAE 4140 were used to manufacture samples with tension screw geometry. Five different, manufacturing process chains, consisting of the process steps heat treatment, turning, and grinding, were applied. After selected process steps, light and SEM micrographs as well as fatigue experiments were performed. The process itself as well as the process parameters influences the properties of the surface layers and the fatigue behavior in a characteristic manner. For example the variation of the feed rate and cutting speed in the hard-turning process leads to significantly different mechanical properties of the surface layers and residual stress states, which could be correlated with the fatigue behavior. The cyclic deformation behavior of the investigated components can be benchmarked equivalently with stress,strain hysteresis as well as high precision temperature and electrical resistance measurements. The temperature and electrical resistance measurements are suitable for component applications and provide an enormous advantage of information about the fatigue behavior. The temperature changes of the failed areas of the samples with tension screw geometry were significantly higher, a reliable identification of endangered areas is thereby possible. A new test procedure, developed at the Institute of Materials Science and Engineering of the University of Kaiserslautern, with inserted load-free-states during constant amplitude loading, provides the opportunity to detect proceeding fatigue damage in components during inspections. [source]

Analysis of temperature distribution near the crack tip under constant amplitude loading

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2008
K. N. PANDEY
ABSTRACT An analytical/numerical method has been developed to find the temperature rise near the crack tip under fatigue loading. The cyclic plastic zone ahead of the crack tip is assumed to be the shape of the source of heat generation and some fraction of plastic work done in cyclic plastic zone as heat generation. Plastic work during fatigue load was found by obtaining stress and strain distribution within the plastic zone by Hutchinson, Rice and Rosengren (HRR) crack tip singularity fields applied to small scale yielding on the cyclic stress strain curve. A two-dimensional conduction heat transfer equation, in moving co-ordinates, was used to obtain temperature distribution around the crack tip. Temperature rise was found to be a function of frequency of loading, applied stress intensity factor and thermal properties of the material. A power,law relation was found between the rise in temperature at a fixed point near the crack tip and range of stress intensity factor. [source]

Fretting fatigue under variable loading below fretting fatigue limit

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2006
Y. KONDO
ABSTRACT The fatigue limit diagram provides the critical condition of non-failure against fatigue under constant amplitude loading. The fatigue limit diagram is usually considered to give the allowable stress if every stress component is kept within the fatigue limit diagram. In the case of variable amplitude fretting fatigue, however, this study showed that fatigue failure could occur even when all stresses were within the fatigue limit diagram. An example of such a condition is a repeated two-step loading such as when the first step stress is R=,1 and the second step stress has a high mean value. The reason why such a phenomenon occurs was investigated. A non-propagating crack was formed by the first step stress even when well below the fatigue limit. The resultant non-propagating crack functioned as a pre-crack for the second step stress with a high mean value. Consequently, fatigue failure occurred even when every stress was within the fatigue limit diagram of constant amplitude loading. The fatigue limit diagram obtained in constant amplitude fatigue test does not necessarily guarantee safety in the case of variable amplitude loading in fretting fatigue. [source]

Fatigue behaviour and life prediction of fibre reinforced metal laminates under constant and variable amplitude loading

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2002
X. R. WU
ABSTRACT Fatigue crack growth of fibre reinforced metal laminates (FRMLs) under constant and variable amplitude loading was studied through analysis and experiments. The distribution of the bridging stress along the crackline in centre-cracked tension (CCT) specimen of FRMLs was modelled numerically, and the main factors affecting the bridging stress were identified. A test method for determining the delamination growth rates in a modified double cracked lap shear (DCLS) specimen was presented. Two models, one being fatigue-mechanism-based and the other phenomenological, were developed for predicting the fatigue life under constant amplitude loading. The fatigue behaviour, including crack growth and delamination growth, of glass fibre reinforced aluminium laminates (GLARE) under constant amplitude loading following a single overload was investigated experimentally, and the mechanisms for the effect of a single overload on the crack growth rates and the delamination growth rates were identified. An equivalent closure model for predicting crack-growth in FRMLs under variable amplitude loading and spectrum loading was presented. All the models presented in this paper were verified by applying to GLARE under constant amplitude loading and Mini-transport aircraft wing structures (TWIST) load sequence. The predicted crack growth rates are in good agreement with test results. [source]

Fatigue crack initiation in naval welded joints: experimental and numerical approaches

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008
D. Thevenet
This work deals with the fatigue behavior of welded joints. The proposed strategy can be split into two stages: the structure shakedown study and the fatigue crack initiation study. Firstly, stabilized elastic stress,strain cycles are obtained in any point of the welded joint by a finite element analysis, taking constant or variable amplitude loadings into account. The second part of this work is the calculation of the fatigue crack initiation period. Under the assumption of a fast elastic shakedown, a recent approach, proposed by Lemaitre et al., based on damage mechanics, can be used to predict the fatigue crack initiation life in a structure subjected to variable and complex loadings. This strategy is used as a post,treatment of the shakedown finite element calculation for the studied welded specimen. As a validation, four,point bending fatigue tests under constant amplitude loading were carried out on welded specimens provided by DCNS group. Good correlations between experimental and calculated fatigue crack initiation lives have been established. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]