Ronald Guillén

Evolution of internal stresses in rolled Zr702α

Internal stresses due to anisotropic thermal and plastic properties were investigated in a rolled Zirconium-α. The thermal stresses induced by a cooling process were predicted using a self-consistent model and compared with experimental results obtained by X-ray diffraction. The study of the elastoplastic response during uniaxial loading was performed along the rolling and the transverse direction of the sheet, considering the influence of the texture and the thermal stresses on the mechanical behaviour. We used an elastoplastic self-consistent formulation and the predicted results are compared with mechanical tests. The role of twinning and slip on the development of internal stresses is also discussed.

A Hygroelastic Self-consistent Model for Fiber-reinforced Composites

Stress analyses are performed in unidirectional fiber-reinforced composites, exposed to ambient fluid, by extending a classical self-consistent model to hygroelastic solicitations. Constitutive laws are given for the macroscopic elastic properties and Coefficients of Moisture Expansion (CME) by considering a jump in moisture content between the fiber and the matrix. Inverse forms for the unknown CME of the constituent matrix are proposed. The macroscopic (ply) and local (fiber and matrix) internal stress states are evaluated for various moisture content ratios between the matrix and the ply. The macroscopic stresses are calculated by using continuum mechanics formalisms and the local stresses are deduced from the scale transition model.

Effect of plastic shearing on damage and texture on Zircaloy-4 cladding tubes : experimental and numerical study

Abstract Experimental evaluation of plastic shearing due to cold rolling Zircaloy-4 (Zy4) cladding tubes has been performed. An experiment design was used to evaluate the influence of three parameters on the shear stress: the feeding, the frequency of rolling steps, and the type of internal lubricant. Calculation and experimental analysis have shown a good correlation between a cumulative damage factor (CDF) and depth of defects in cold-pilgered tubes. The CDF depends strongly on the shear strain e zr . Texture simulations, using a visco-plastic self-consistent (VPSC) model, have been performed and compared with experimental pole figures (PF) obtained by X-ray diffraction. A very good agreement is obtained between experimental and simulated pole figures, specially in radial and axial directions (RD–AD) plane. Results have shown that a shear component in the strain rate tensor is necessary, and that the critical resolved shear stresses (CRSS) must be changed during pilgering to take into account the real pilgering conditions.

On an analytical self-consistent model for internal stress prediction in fiber-reinforced composites submitted to hygroelastic load

The aim of this work is to demonstrate a fully explicit analytical micromechanical self-consistent approach dedicated to mechanical states prediction in both the fiber and the matrix of composite structures submitted to a transient hygroelastic load. The analytical forms obtained are applied to the case of carbon-epoxy composites. Rigorous continuum mechanics formalisms are used for the determination of the required time and space-dependent macroscopic stresses. The reliability of the new approach is checked through a comparison between the local stress states calculated in both the resin and the fiber according to the new closed-form solutions and the equivalent numerical model.

Determination of single-crystal elasticity constants in a cubic phase within a multiphase alloy: X-ray diffraction measurements and inverse-scale transition modelling

The scope of this work is the determination of single-crystal elastic properties from X-ray diffraction stress analysis performed on multiphase polycrystals. An explicit three-scale multiphase inverse self-consistent model is developed in order to express the single-crystal elasticity constants of a cubic phase as a function of its X-ray elasticity constants. The model is verified in the case of single-phase materials. Finally, it is applied to a two-phase (α+β) titanium-based alloy (Ti-17) and, as a result, the Ti-17 β-phase single-crystal elasticity tensor is estimated.

Mesoscopic residual stresses of plastic origin in zirconium: interpretation of X-ray diffraction results

Complementary methods have been used to analyse residual stresses in a heat-treated Zr702 sheet which had undergone uniaxial plastic deformation: X-ray diffraction and self-consistent models. The elastoplastic self-consistent model has been used to simulate the experiments and exhibits agreement with experimental data. X-ray diffraction analysis in the rolling direction shows opposite stress values for {[10\bar{1}4]} and {[20\bar{2}2]} planes, respectively. The measured strains were generated by an anisotropic plastic deformation. The comparison between ∊ϕψ versus sin2ψ and simulations confirms that prismatic slip is the main active deformation mode. Plastic incompatibility stress in X-ray measurements should be taken into account in order to make a correct interpretation of the experimental data.

Extension of Mori-Tanaka Approach to Hygroelastic Loading of Fiber-reinforced Composites - Comparison with Eshelby-Kroner Self-consistent Model

The scale transition model historically proposed by Mori and Tanaka to predict the average and local elastic behavior of heterogeneous structures is extended to hygro-elastic load for the first time. Explicit constitutive laws satisfying the fundamental assumptions of the model are given for the determination of the effective macroscopic coefficients of moisture expansion (CME) in composite structures by considering a jump in moisture content between the fiber and the matrix. Explicit forms are also given for the calculation of local (fiber and matrix scale) internal stress states from the localization of the macroscopic hygro-mechanical states (ply scale). Comparisons for several compositions of composite structures (volume fraction of the constituents, i.e., the epoxy matrix and the reinforcing fibers) are performed between the numerical predictions given by the Mori-Tanaka model extended to hygro-elastic load and the recently proposed Eshelby-Kroner self-consistent hygro-elastic model. Discrepancies in the calculations appearing with an increase of the reinforcing fiber volume fraction are extensively discussed to conclude on the limitations of the micro-mechanical approach developed in the present work.

Determining Ti-17 β-Phase Single-Crystal Elasticity Constants through X-Ray Diffraction and Inverse Scale Transition Model

The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray diffraction lattice strains measurements performed on multi-phase polycrystals submitted to mechanical load through a bending device. An explicit three scales inverse self-consistent model is developed in order to express the SEC of a cubic phase, embedded in a multi-phase polycrystal, as a function of its X-ray Elasticity Constants. Finally, it is applied to a two-phases (α+β) titanium based alloy (Ti-17), in order to estimate Ti-17 β-phase unknown SEC. The purpose of the present work is to account the proper microstructure of the material. In particular, the morphologic texture of Ti-17 a-phase, i.e. the relative disorientation of the needle-shaped grains constituting this phase, is considered owing to the so-called Generalized Self-Consistent model.

Texture and residual-stresses analysis in Zircaloy-4 cylindrical samples

Texture and residual-stress analysis using X-ray diffraction have been carried out on cylindrical Zircaloy-4 samples in cold-worked and finished state. The (00.2) pole figure of finished tubes shows an important asymmetry in the tangential direction (TD) not observed on unrolled tubes. This asymmetry vanishes at a 5-μm depth. A noticeable variation of the texture index J has been pointed out within the first micrometers from the surface of the tubes. Strain measurements in tangential and longitudinal directions have been carried out on the (10.4) and (20.2) planes. In the tangential (hoop) direction, compressive stress on the outer surface decreases rapidly in the first layers and remains constant at the analysed depth. Axial stress analysis shows the opposite sign for the two different diffracting planes on the cold-worked tubes, indicating the existence of second-order stresses.

Interpretation of X‐Ray Stress Measurement and Evaluation of Internal Residual Stresses in Rolled α‐Ti40 Using Self‐Consistent Models

Internal stresses due to anisotropic thermal and plastic properties were investigated in rolled α-titanium. The thermal stresses induced by a cooling process were predicted using a self-consistent model and compared with experimental results obtained by X-ray diffraction. A study of the elastoplastic response after uniaxial loading was performed along the rolling and the transverse direction of the sheet. Using an elastoplastic self-consistent model, the predicted results were compared with X-ray diffraction and mechanical tests. Theoretical and experimental results agree in their tendencies. The comparison between e Φψ versus sin 2 ψ and simulations confirms that prismatic slip is the main active deformation mode.