Fatigue behaviour of unidirectional carbon-cord reinforced composites and parametric models for life prediction

© 2017 Taylor & Francis Group, London, UK. Unidirectional Carbon Cord reinforced HNBR composites (CF-HNBR) were prepared and fatigue tests under stress control were performed under non-relaxed tension-tension conditions. In this paper, various Constant Life Diagrams (CLD) that are based on different theoretical formulations have been applied to the measured fatigue data of the CF-HNBR composites. The results show that the predictions made by piecewise CLD and modified Harries CLD produce the most accurate results. In addition, a novel experimental set-up is described that replicates in a simplified way the real-pulley situation encountered under typical service conditions to investigate the effect of the bending curvature on the lifetime of the composite subject to coupled tension and bending conditions

Constitutive modelling of Sandvik 1RK91

A physically based constitutive equation is being developed for the maraging\ud stainless steel Sandvik 1RK91. The steel is used to make precision parts. These parts are formed through multistage forming operations and heat treatments from cold rolled and annealed sheets. The specific alloy is designed to be thermodynamically unstable, so that deformation even at room temperatures can bring about a change in the phase of face centred cubic austenite to either hexagonal closed packed martensite and/or, body centred cubic martensite. This solid state phase change is a function of the strain path, strain, strain rate and temperature. Thus, the fraction of the new phase formed depends on the state of stress at a given location in the part being formed. Therefore a set of experiments is being conducted in order to quantify the stress-strain behavior of this steel under various stress states, strain, strain rate as well as temperature. A magnetic sensor records the fraction of ferromagnetic martensite formed from paramagnetic austenite. A thermocouple as well as an infra red thermometer is used to log the change in temperature of the steel during a mechanical test. The force-displacement data are converted to stress-strain data after correcting for the changes in strain rate and temperature. These data are then cast into a general form of constitutive equation and the transformation equations are derived from Olson-Cohen type functions

From dry yarns to complex 3D woven fabrics: a unified simulation methodology for deformation mechanics of textiles in tension, shear and draping

Common methods of modelling the behaviour of fibrous materials, such as yarns and (woven) fabrics, is to treat them as continuous solids. The fibrous behaviour is then taken into account by appropriate constitutive laws. However, the development of such constitutive laws is very complex and requires several specificities (large deformations, orthotropic material behaviour, local crushing, …). Furthermore, by treating the material as a solid material important information about the micromechanics is “lost”. This presentation will show a more viable modelling methodology to simulate the deformation mechanics of fibrous materials and it is based on the use of virtual fibres. This recently developed method effectively takes the fibrous behaviour into account by modelling a yarn as a bundle of virtual fibres, see Figure 1. Each virtual fibre is modelled as a chain of truss elements in Abaqus\Explicit. The virtual fibres can realign themselves and slide relative to each other resembling the mechanics in a real yarn. The advantages of this method will be illustrated by applying it to some very complex problems such as the mechanical behaviour of 3D woven fabrics, draping behaviour of fabrics and stitching of sandwich panels

Closed form solution of the return mapping algorithm in elastoplasticity

In the present work a return mapping algorithm is discussed for small strain elastoplasticity boundary value problems with an exact closed form solution of the local constitutive equations. Nonlinear kinematic hardening rules are adopted in modelling kinematic hardening behavior of ductile materials. The local solution of the constitutive equations is expressed by only one nonlinear scalar equation which is subsequently reduced to a single variable algebraic equation. Due to the straightforward form of the nonlinear scalar equation the analytical solution of the algebraic equation is found in exact closed form. A remarkable advantage of the present approach is that no iterative solution method is used to solve the local constitutive equations in three-dimensional elastoplasticity. Numerical applications and computational results are reported in order to illustrate the robustness and effectiveness of the proposed algorithmic procedure

Wall Adhesion and Constitutive Modelling of Strong Colloidal Gels

Wall adhesion effects during batch sedimentation of strongly flocculated colloidal gels are commonly assumed to be negligible. In this study in-situ measurements of colloidal gel rheology and solids volume fraction distribution suggest the contrary, where significant wall adhesion effects are observed in a 110mm diameter settling column. We develop and validate a mathematical model for the equilibrium stress state in the presence of wall adhesion under both viscoplastic and viscoelastic constitutive models. These formulations highlight fundamental issues regarding the constitutive modeling of colloidal gels, specifically the relative utility and validity of viscoplastic and viscoelastic rheological models under arbitrary tensorial loadings. The developed model is validated against experimental data, which points toward a novel method to estimate the shear and compressive yield strength of strongly flocculated colloidal gels from a series of equilibrium solids volume fraction profiles over various column widths.Comment: 37 pages, 12 figures, submitted to Journal of Rheolog

A multiscale constitutive model for intergranular stress corrosion cracking in type 304 austenitic stainless steel

Intergranular stress corrosion cracking (IGSCC) is a fracture mechanism in sensitised austenitic stainless steels exposed to critical environments where the intergranular cracks extends along the network of connected susceptible grain boundaries. A constitutive model is presented to estimate the maximum intergranular crack growth by taking into consideration the materials mechanical properties and microstructure characters distribution. This constitutive model is constructed based on the assumption that each grain is a two phase material comprising of grain interior and grain boundary zone. The inherent micro-mechanisms active in the grain interior during IGSCC is based on crystal plasticity theory, while the grain boundary zone has been modelled by proposing a phenomenological constitutive model motivated from cohesive zone modelling approach. Overall, response of the representative volume is calculated by volume averaging of individual grain behaviour. Model is assessed by performing rigorous parametric studies, followed by validation and verification of the proposed constitutive model using representative volume element based FE simulations reported in the literature. In the last section, model application is demonstrated using intergranular stress corrosion cracking experiments which shows a good agreement