Tailored metal matrix composites for high-temperature performance

A multi-objective tailoring methodology is presented to maximize stiffness and load carrying capacity of a metal matrix cross-ply laminated at elevated temperatures. The fabrication process and fiber volume ratio are used as the design variables. A unique feature is the concurrent effects from fabrication, residual stresses, material nonlinearity, and thermo-mechanical loading on the laminate properties at the post-fabrication phase. For a (0/90)(sub s) graphite/copper laminate, strong coupling was observed between the fabrication process, laminate characteristics, and thermo-mechanical loading. The multi-objective tailoring was found to be more effective than single objective tailoring. Results indicate the potential to increase laminate stiffness and load carrying capacity by controlling the critical parameters of the fabrication process and the laminate

A unified creep-plasticity model suitable for thermo-mechanical loading

An experimentally based unified creep-plasticity constitutive model was implemented for 1070 steel. Accurate rate and temperature effects were obtained for isothermal and thermo-mechanical loading by incorporating deformation mechanisms into the constitutive equations in a simple way

Investigating the time-dependent behaviour of Boom clay under thermo-mechanical loading

Among the various laboratory studies to investigate the Thermo-Hydro-Mechanical (THM) behaviour of Boom clay, relatively few were devoted to the time dependent behaviour, limiting any relevant analysis of the long-term behaviour of the disposal facility. The present work aims at investigating the time-dependent behaviour of Boom clay under both thermal and mechanical loading. High-pressure triaxial tests at controlled temperatures were carried out for this purpose. The tests started with constant-rate thermal and/or mechanical consolidation and ended with isobar heating and/or isothermal compression at a constant stress rate or by step loading. Significant effects of temperature as well as of compression and heating rates were observed on the volume change behaviour. After being loaded to a stress lower than the pre-consolidation pressure (5 MPa) at a low temperature of 25\degree C and at a rate lower than 0.2 kPa/min, the sample volume changes seemed to be quite small, suggesting a full dissipation of pore water pressure. By contrast, after being subjected to high loading and heating rates (including step loading or step heating), the volume changes appeared to be significant, particularly in the case of stresses much higher than the pre-consolidation pressure. Due to low permeability, full consolidation of Boom clay required a long period of time and it was difficult to distinguish consolidation and creep from the total volume change with time

Thermo-mechanical loading of intact rock and discontinuities

Coupled thermo-mechanical processes present challenges in a number of areas of geological understanding. Thermal loading can occur due to the natural geothermal gradient or the introduction of an anthropogenic heat source in a rock mass. In this study the thermo-mechanical behaviour of intact rock and discontinuities is investigated through both laboratory experiments and their numerical simulations. A new method was devised for creating synthetic discontinuous specimens with representative discontinuity topography suitable for thermo-mechanical triaxial testing. Different synthetic compositions were trialled to achieve a composition representative of a sedimentary lithology. Whilst synthetic discontinuities could repeatedly be created with representative topography, a synthetic composition with mechanical characteristics of a sedimentary lithology could not be created. Following testing of synthetic specimens, thermo-mechanical triaxial experiments were then performed on intact specimens of sandstone at temperatures up to 100°C. Additionally these experiments were repeated under the same thermo-mechanical conditions on specimens with a single pre-existing discontinuity running through the specimens at 30° from the vertical, allowing shearing to occur on the discontinuity under triaxial conditions. Laboratory results of testing on sandstone showed a reduction of up to 15% peak strength with increasing thermal loading between ambient temperature and 100°C for intact specimens, whereas specimens with discontinuities present an initial increase in discontinuity peak shear strength with increasing thermal loading to 50°C, before a reduction in peak shear strength thereafter. The laboratory experiments were replicated using thermo-mechanically coupled discrete element method grain based models. The grain based models highlight the build up of thermally induced localised stresses within the intact specimens due to grain scale heterogeneity of thermal properties, resulting in the initiation and accumulation of tensile thermal micro-cracks, causing reduced strength. When a discontinuity is introduced to the models, the discontinuity allows room for thermal expansion resulting in thermal closure, until maximum thermal closure is reached. Thermal micro-cracking then occurs as observed in the intact specimens, causing a reduction in strength. These findings offer new contributions to the understanding of the thermo-mechanical behaviour of intact rock and discontinuities

Finite Strain Constitutive Modelling of Shape Memory Alloys Considering Partial Phase Transformation with Transformation-Induced Plasticity

This paper presents a unified modelling effort to describe partial phase transformation during cyclic thermo-mechanical loading in Shape Memory Alloys (SMA). To this purpose, a three-dimensional (3D) finite strain constitutive model considering TRansformation-Induced Plasticity (TRIP) is combined with a modified hardening function to enable the accurate and efficient prediction of partial transformations during cyclic thermo-mechanical loading. The capabilities of the proposed model are demonstrated by predicting the behavior of the material under pseudoelastic and actuation operation using finite element analysis. Numerical results of the modified model are presented and compared with the original model without considering the partial transformation feature as well as with uniaxial actuation experimental data. Various aspects of cyclic material behavior under partial transformation are analyzed and discussed for different SMA systems

Calculation of a lower bound ratchet limit part 2 : Application to a pipe intersection and dissimilar material join

In an accompanying paper in this issue a lower bound method based on Melan's theorem was derived and implemented into the Linear Matching Method ratchet analysis procedure. This paper presents a ratchet analysis of a pipe intersection subject to cyclic thermo-mechanical loading using the proposed numerical technique. This work is intended to demonstrate the applicability of the lower bound method to a structure commonly seen in industry and also to better understand the behaviour of this component when subjected to cyclic loading. The pipe intersection considered here has multiple materials with temperature dependent properties. Verification of the results is given via full elastic-plastic analysis in Abaqus

Metal Matrix Laminate Tailoring (MMLT) code: User's manual

The User's Manual for the Metal Matrix Laminate Tailoring (MMLT) program is presented. The code is capable of tailoring the fabrication process, constituent characteristics, and laminate parameters (individually or concurrently) for a wide variety of metal matrix composite (MMC) materials, to improve the performance and identify trends or behavior of MMC's under different thermo-mechanical loading conditions. This document is meant to serve as a guide in the use of the MMLT code. Detailed explanations of the composite mechanics and tailoring analysis are beyond the scope of this document, and may be found in the references. MMLT was developed by the Structural Mechanics Branch at NASA Lewis Research Center (LeRC)

An investigation of the crack propagation in tool steel X38CrMoV5(AISI H11) in SET specimens

An approach is proposed for the evaluation of surface fatigue damage of hot forming tools that undergo severe thermo mechanical loading. Fatigue crack propagation in a hot work tool steel X38CrMoV5-47HRC is investigated using single-edge cracked tension specimens with 3 different thicknesses (2.5, 1, 0.6 mm) and two R-values. The stress intensity factor is evaluated with ABAQUS®. Paris curves are established for the crack propagation experiments

Методика и результаты исследования влияния смешанных мод дефформирования на характеристики статической трещиностойкости теплоустойчивых сталей с учетом предварительного термомеханического нагружения

It is set that the component of longitudinal shear diminishes the "positive effect of PTS", i.e. increase of fracture toughness as a result of preliminary thermo mechanical loading. It is shown that during determination of fracture toughness KIIIc at the loading of prismatic specimen of eventual thickness by a longitudinal shear, on front of crack displacement will be realized as in transversal (mode II) so in longitudinal (mode III) directions