The Experts below are selected from a list of 1926 Experts worldwide ranked by ideXlab platform
Martyn J Pavier - One of the best experts on this subject based on the ideXlab platform.
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the effect of cold expansion on fatigue crack growth from open holes at room and high temperature
International Journal of Fatigue, 2001Co-Authors: V Lacarac, David J Smith, Martyn J PavierAbstract:Abstract In this paper a series of residual stress measurements and fatigue crack growth tests have been carried out using aluminium alloy 2650 specimens containing cold expanded and non cold expanded holes. Residual stress measurements have been done after cold expansion and after various Loading and temperature conditions. In order to measure an angular variation of residual stresses, X-ray and a new technique called the Garcia–Sachs method have been employed. Results revealed that residual stress relaxation occurred as a result of exposure at 150°C. The magnitude of relaxation was shown to be dependent on the level and the sign of Externally Applied Load. Fatigue crack growth tests have been carried out at 20°C and 150°C for both cold expanded and non-cold expanded conditions. Fatigue crack growth rates in specimens containing cold expanded fastener holes were affected significantly by elevated temperature exposure. Depending on the exposure time and Loading conditions the fatigue life improvement was found to be between one and greater than 10 for tests at 20°C.
David J Smith - One of the best experts on this subject based on the ideXlab platform.
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a combined experimental and modelling approach to elastic plastic crack driving force calculation in the presence of residual stresses
Experimental Mechanics, 2016Co-Authors: Harry Coules, David J Smith, Paulo Orrock, Abburi K Venkata, Thilo PirlingAbstract:Since all residual stress measurement methods have inherent limitations, it is normally impractical to completely characterise a three-dimensional residual stress field by experimental means. This lack of complete information makes it difficult to incorporate measured residual stress data into the analysis of elastic–plastic fracture without resorting to simplified methods such as the Failure Assessment Diagram (FAD) approach. We propose a technique in which the complete residual stress field is reconstructed from measurements and used in finite element analysis of the fracture process. Residual elastic strains and stresses in three-point bend fracture specimens were measured using neutron diffraction and an iterative method was used to generate a self-consistent estimate of the complete residual stress field. This enabled calculation of the J contour integral for a specimen acted on by both residual stress and an Externally-Applied Load, allowing the interaction between residual and Applied stress to be observed in detail.
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the effect of cold expansion on fatigue crack growth from open holes at room and high temperature
International Journal of Fatigue, 2001Co-Authors: V Lacarac, David J Smith, Martyn J PavierAbstract:Abstract In this paper a series of residual stress measurements and fatigue crack growth tests have been carried out using aluminium alloy 2650 specimens containing cold expanded and non cold expanded holes. Residual stress measurements have been done after cold expansion and after various Loading and temperature conditions. In order to measure an angular variation of residual stresses, X-ray and a new technique called the Garcia–Sachs method have been employed. Results revealed that residual stress relaxation occurred as a result of exposure at 150°C. The magnitude of relaxation was shown to be dependent on the level and the sign of Externally Applied Load. Fatigue crack growth tests have been carried out at 20°C and 150°C for both cold expanded and non-cold expanded conditions. Fatigue crack growth rates in specimens containing cold expanded fastener holes were affected significantly by elevated temperature exposure. Depending on the exposure time and Loading conditions the fatigue life improvement was found to be between one and greater than 10 for tests at 20°C.
Jerry H Qi - One of the best experts on this subject based on the ideXlab platform.
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two way reversible shape memory effects in a free standing polymer composite
Smart Materials and Structures, 2011Co-Authors: Kristofer K Westbrook, Patrick T Mather, Vikas Parakh, Martin L Dunn, Qi Ge, Jerry H QiAbstract:Shape memory polymers (SMPs) have attracted significant research efforts due to their ease in manufacturing and highly tailorable thermomechanical properties. SMPs can be temporarily programmed and fixed in a nonequilibrium shape and are capable of recovering the original undeformed shape upon exposure to a stimulus, the most common being temperature. Most SMPs exhibit a one-way shape memory (1W-SM) effect since one programming step can only yield one shape memory cycle; an additional shape memory cycle requires an extra programming step. Recently, a novel SMP that demonstrates both 1W-SM and two-way shape memory (2W-SM) effects was demonstrated by one of the authors (Mather). However, to achieve two-way actuation this SMP relies on a constant Externally Applied Load. In this paper, an SMP composite where a pre-stretched 2W-SMP is embedded in an elastomeric matrix is developed. This composite demonstrates 2W-SM effects in response to changes in temperature without the requirement of a constant external Load. A transversal actuation of ~ 10% of actuator length is achieved. Cyclic tests show that the transversal actuation stabilizes after an initial training cycle and shows no significant decreases after four cycles. A simple analytic model considering the programming stress and actuator dimensions is presented and shown to agree well with the transverse displacement of the actuator. The model also predicts that larger actuation can be achieved when larger pre-stretch of 2W-SMP is used. The scheme used for this polymer composite can promote the design of new shape memory composites at micro- and nano-length scales to meet different application requirements.
V Lacarac - One of the best experts on this subject based on the ideXlab platform.
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the effect of cold expansion on fatigue crack growth from open holes at room and high temperature
International Journal of Fatigue, 2001Co-Authors: V Lacarac, David J Smith, Martyn J PavierAbstract:Abstract In this paper a series of residual stress measurements and fatigue crack growth tests have been carried out using aluminium alloy 2650 specimens containing cold expanded and non cold expanded holes. Residual stress measurements have been done after cold expansion and after various Loading and temperature conditions. In order to measure an angular variation of residual stresses, X-ray and a new technique called the Garcia–Sachs method have been employed. Results revealed that residual stress relaxation occurred as a result of exposure at 150°C. The magnitude of relaxation was shown to be dependent on the level and the sign of Externally Applied Load. Fatigue crack growth tests have been carried out at 20°C and 150°C for both cold expanded and non-cold expanded conditions. Fatigue crack growth rates in specimens containing cold expanded fastener holes were affected significantly by elevated temperature exposure. Depending on the exposure time and Loading conditions the fatigue life improvement was found to be between one and greater than 10 for tests at 20°C.
Pierreyves Hicher - One of the best experts on this subject based on the ideXlab platform.
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micromechanical modelling for effect of inherent anisotropy on cyclic behaviour of sand
International Journal of Solids and Structures, 2010Co-Authors: Zhenyu Yin, Ching S Chang, Pierreyves HicherAbstract:Abstract The inherent anisotropy more or less exists in sand when preparing samples in laboratory or taking from field. The purpose of this paper is to model cyclic behaviour of sand by means of a micromechanical approach considering inherent anisotropy. The micromechanical stress–strain model developed in an earlier study by Chang and Hicher (2005) is enhanced to account for the stress reversal on a contact plane and the density state-dependent dilatancy. The enhanced model is first examined by simulating typical drained and undrained cyclic tests in conventional triaxial conditions. The model is then used to simulate drained cyclic triaxial tests under constant p ′ on Toyoura sand with different initial void ratios and different levels of p ′, and undrained triaxial tests on dense and loose Nevada sand. The applicability of the present model is evaluated through comparisons between the predicted and the measured results. The evolution of local stresses and local strains at inter-particle planes due to Externally Applied Load are discussed. All simulations have demonstrated that the proposed micromechanical approach is capable of modelling the cyclic behaviour of sand with inherent and induced anisotropy.
