Effects Of Strain Distribution Research Articles

Thermal buckling solutions of generic metallic and laminated structures: Total and updated Lagrangian formulations via refined beam elements

The thermal buckling behavior of metallic and laminated beams/plates is investigated using a linearized stability analysis. By selecting different reference frames, two distinct types of 3 D stability equations can be generated using total and updated Lagrangian formulations (TLF and ULF). Various beam theory kinematics can be obtained within the framework of 1 D Carrera Unified Formulation (CUF) by employing an arbitrary expansion of the generalized variables. More precisely, an improved hierarchical Legendre expansion (IHLE) is used to formulate the Layer-Wise (LW) model in a robust manner. Additionally, using a finite element approximation in conjunction with CUF-IHLE, the obtained stability equations are discretized into a set of algebraic equations. The critical temperatures predicted by TLF- and ULF-based CUF-IHLE models are compared using numerical examples of beams and plates with varying boundary conditions, lamination schemes, and thickness-to-width ratios. Both models are validated for correctness using the commercial software ABAQUS. Besides, the effect of strain distribution during the pre-buckling stage is evaluated in the plate-like structure using one- and two-step analyses.

Effect of strain distribution on the evolution of α phase and texture for dual-phase titanium alloy during multi-pass forging process

Abstract The evolution of microstructure and texture of Ti-6Al-4V alloy during the multi-pass forging process were investigated in the present work. By using the integrated approaches of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD), the effect of strain distribution on texture evolution was discussed. Results show that the strain distribution has a significant effect on morphology and volume fraction of primary α phase. The microstructural homogeneity of ingot is enhanced after multi-pass forging. With the progressing of forging passes, the volume fraction of αp increases remarkably and the intensity of texture components decreases gradually. Besides, the waved-like type dislocations were found be activated preferentially during first pass forging process, and then + type dislocations were activated with the progressing of forging passes. These results ultimately contribute to understanding of the microstructure evolution behavior, favoring development of microstructure controlling technologies for dual-phase titanium alloys.

The effect of strain distribution on microstructural developments during forging in a newly developed nickel base superalloy

In the current study, the effect of strain distribution in a simple forging geometry on the propensity for recrystallization, and its impact on mechanical properties has been investigated in a newly developed experimental nickel-based superalloy. The new alloy was produced via a Powder Metallurgy (PM) route and was subsequently Hot Isostatic Processed (HIP), isothermally forged, and heat treated to produce a coarse grain microstructure with average grain size of 23–32μm. The alloy was examined by means of Electron Back-Scatter Diffraction (EBSD) to characterise the microstructural features such as grain orientation and morphology, grain boundary characteristics and the identification of potential Prior Particle Boundaries (PPBs) throughout each stage of the processing route. Results at the central region of the cross-section plane parallel to the loading direction showed significant microstructural differences across the forging depth. This microstructural variation was found to be highly dependent on the value of local strain imparted during forging such that areas of low effective strain showed partial recrystallisation and a necklace grain structure was observed following heat treatment. Meanwhile, a fully recrystallised microstructure with no PPBs was observed in the areas of high strain values, in the central region of the forging.

Analytical study on effects of strain distribution in welding start/end on welding distortion

A welding distortion prediction method based on the inherent strain concept is presented. In the proposed method, welding distortion of large-welded structures could be estimated by elastic analysis using the result of thermal-elastic–plastic analysis and the result of smaller welded joints or components. Thermal-elastic–plastic analysis is performed to calculate residual plastic strain distribution, which is the input data for the elastic analysis of welding distortion. The obtained residual plastic strain distribution is mapped to non-deformed finite element models to calculate welding distortion by elastic analysis. The mapping procedure is done in different ways for welding start/end parts and the rest of the weld length in order to take into consideration the unsteady strain distribution at the start/end of welds. For start/end parts, strain distribution used is identical with thermal-elastic–plastic analysis. For the part except start/end parts, strain distribution obtained by thermal-elastic–plastic analysis is extracted from the centre of weld length and is extruded along the welding direction. The proposed method was applied to the welding distortion prediction of joints with weld length of 900 and 1200 mm based on the thermal-elastic–plastic analysis result of a joint with weld length 600 mm. The estimated results were in good agreement with the thermal-elastic–plastic analysis results of models of corresponding weld length to show the validity of the proposed method.

The Effect of Strain Distribution on Abnormal Grain Growth in Cu Thin Films

The effect of intrinsic strain on grain growth in Cu thin films was studied by both plan-view and cross-sectional scanning ion microscope in a focused ion beam system. Significant grain growth with bimodal grain size distribution was observed during room temperature storage in the Cu films which were deposited on the Si 3 N 4 substrates by a sputter-deposition technique. In the thick Cu films, a non-uniform grain size distribution was observed along a direction normal to the film surface: the large grains were observed at the location close to the substrate surface. This grain size distribution coincided with inhomogeneous strain distribution normal to the film surface. We concluded that the grain growth in the Cu thin films was facilitated by the strain intrinsic in the Cu films deposited on the rigid substrates, and that strain (or stress) introduced in the films was a primary factor to induce the grain growth in the Cu films at room temperature.

Stress Profile Dependence of the Optical Properties in Strained Quantum Wire Arrays

The effects of strain distribution in quantum wire arrays have been analyzed using a finite-element method including both the hydrostatic and shear strain components. Their effects on the optical properties of the quantum wire arrays are assessed for various types of stress profiles by calculating the optical gain and the polarization dependence. The results show unique polarization dependency, which can be exploited either for the single polarization or the polarization-independent operation in quantum wire photonic devices.

Structural characterization of InGaAs/GaAs quantum dots superlattice infrared photodetector structures

InGaAs/GaAs quantum dots (QDs) superlattice grown by molecular beam epitaxy (MBE) at different substrate temperatures for fabricating 8–12 μm infrared photodetector were characterized by transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL). High-quality QDs superlattice can be achieved by higher growth temperature. Cross-sectional TEM shows the QDs in the successive layers are vertically aligned along growth direction. Interaction of partial vertically aligned columns leads to a perfect vertical ordering. With increasing number of bilayers, the average QDs size becomes larger in height and rapidly saturates at a certain value, while average lateral length nearly preserves initial size. This change leads to the formation of QDs homogeneous in size and of a particular shape. The observed self-organizations are attributed to the effect of strain distribution at QDs on the kinetic growth process. DCXRD measurement shows two sets of satellite peaks which corresponds to QDs superlattice and multi quantum wells formed by the wetting layers. Kinematical simulations of the wetting layers indicate that the formation of QDs is associated with a decrease of the effective indium content in the wetting layers.