Topic
Creep
About: Creep is a research topic. Over the lifetime, 48630 publications have been published within this topic receiving 772872 citations.
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01 Sep 1979
TL;DR: In this article, a nonlinear damage relation, containing the axial strain history and a time integral over the stress history, is proposed for the case of one-dimensional time dependent tensile stress.
Abstract: : A nonlinear damage relation, containing the axial strain history and a time integral over the stress history, is proposed for the case of one-dimensional time dependent tensile stress. Nonlinear steady and transient creep terms are included in the axial strain relation, and elastic and creep Poisson's ratios are introduced into the lateral strain relation. Using these relations, complete damage solutions are obtained for the constant stress rate, step stress, relaxation and constant load tests. Observations are made concerning the associated rupture times. (Author)
21 citations
TL;DR: In this paper, a simple kinetic model was proposed to explain the shape of the creep curves of germanium single crystals loaded in tension and in bending, in which the dislocations are generated by (surface) sources and move with a uniform velocity over their glide planes.
21 citations
TL;DR: In this paper, the authors developed the viscoplasticity theory based on overstress (VBO) that can model unusual deformation behaviors in metallic alloys and polymers at ambient and elevated temperatures.
Abstract: Transient tests are used to demonstrate unusual or even paradoxical deformation behaviors in metallic alloys and polymers at ambient and elevated temperatures. Included are repeated relaxation tests and creep tests of short duration. It is shown that creep rate need not increase with a stress increase and that, at the same stress level, creep rate can be different on loading and unloading. Also, a stress magnitude increase can be found during relaxation. Once steady inelastic flow is reached, the relaxation rate is nearly independent of the stress and strain at which relaxation starts; it depends mainly on the preceding prior inelastic strain rate. These phenomena can be modeled using an overstress (effective stress) dependence of inelastic rate of deformation and a proper evolution law for a single state variable, the equilibrium stress (back stress) within the context of a “unified” state variable theory. The author and his students have developed the viscoplasticity theory based on overstress (VBO) that can model these unusual behaviors.
21 citations
TL;DR: In this article, a four-decade drop in insulation resistance between adjacent leads with visible bridging of corrosion products was measured between adjacent lead with an MFG exposure of 10 days, and corrosion products were found to be copper salts.
Abstract: This paper describes tests and analysis of creep corrosion on plastic encapsulated electronic components with Ni/Pd or Ni/Pd/Au plated copper leadframes. Samples were subjected to three standard mixed flowing gas (MFG) tests to simulate corrosion effects in an accelerated manner, which included Telcordia Outdoor, and Battelle Class III Telcordia Indoor MFG environments. With an MFG exposure of 10 days, creep corrosion was observed over the plastic molding compound surface in the first two of the test environments. The formation and thickness of creep corrosion products on molding compound surface were characterized by microscopic observation. A four-decade drop in insulation resistance was measured between adjacent leads with visible bridging of corrosion products. Energy dispersive spectroscopy (EDS) was used to assess the elemental composition of corrosion products on both the component leads and the molding compound surfaces, and corrosion products were found to be copper salts. Sample pre-conditions, including surface cleaning, mold compound surface roughness, additional lead scratches, and applied voltage biases, were evaluated, and found to have no significant effects on the creep corrosion process. Conformal coating of the components was found to be an effective mitigation strategy to eliminate creep corrosion on packages with noble metal pre-plated leadframes.
21 citations
Journal Article•
TL;DR: In this article, a fundamental model of mat stress relaxation was developed based on the compressive stress relaxation of wood flakes and Poisson distribution of flake overlaps formed in the mat.
Abstract: To improve our understanding of the wood composite hot-pressing process, viscoelastic consolidation of wood flake mats was investigated in terms of constituent flake properties and mat formation. A fundamental model of mat stress relaxation was developed based on the compressive stress relaxation of wood flakes and Poisson distribution of flake overlaps formed in the mat. Both stress relaxation and creep of wood flakes and flake mats at ambient condition were experimentally tested and analyzed. The results showed that the stress relaxation of wood flakes at different levels of compression follows linear double logarithmic relationships with varying slopes or rates of stress relaxation. The mat stress relaxation model was validated by comparing the model predictions with the experimental data. Like stress relaxation, creep of flakes also varies with the level of compression. Due to porosity difference, creep of flake mats is not quantitatively comparable to creep of flakes in terms of relative creep strain. Instead, relative creep compaction ratio of mats is comparable to that of wood flakes.
21 citations