Strain rate dependence in plasticized and un-plasticized PVC

An experimental and analytical investigation has been made into the mechanical behaviour of two poly (vinyl chloride) (PVC) polymers – an un-plasticized PVC and a diisononyl phthalate (DINP)-plasticized PVC. Measurements of the compressive stress-strain behaviour of the PVCs at strain rates ranging from 10−3 to 103s−1 and temperatures from − 60 to 100∘C are presented. Dynamic Mechanical Analysis was also performed in order to understand the material transitions observed in compression testing as the strain rate is increased. This investigation develops a better understanding of the interplay between the temperature dependence and rate dependence of polymers, with a focus on locating the temperature and rate-dependent material transitions that occur during high rate testing

Strain rate dependency of laser sintered polyamide 12

Parts processed by Additive Manufacturing can now be found across a wide range of applications, such as those in the aerospace and automotive industry in which the mechanical response must be optimised. Many of these applications are subjected to high rate or impact loading, yet it is believed that there is no prior research on the strain rate dependence in these materials. This research investigates the effect of strain rate and laser energy density on laser sintered polyamide 12. In the study presented here, parts produced using four different laser sintered energy densities were exposed to uniaxial compression tests at strain rates ranging from 10−3 to 10+3 s−1 at room temperature, and the dependence on these parameters is presented

Probabilistic estimation of the constitutive parameters of polymers

The Mulliken-Boyce constitutive model predicts the dynamic response of crystalline polymers as a function of strain rate and temperature. This paper describes the Mulliken-Boyce model-based estimation of the constitutive parameters in a Bayesian probabilistic framework. Experimental data from dynamic mechanical analysis and dynamic compression of PVC samples over a wide range of strain rates are analyzed. Both experimental uncertainty and natural variations in the material properties are simultaneously considered as independent and joint distributions; the posterior probability distributions are shown and compared with prior estimates of the material constitutive parameters. Additionally, particular statistical distributions are shown to be effective at capturing the rate and temperature dependence of internal phase transitions in DMA data

Strain rate dependency of laser sintered polyamide 12

Parts processed by Additive Manufacturing can now be found across a wide range of applications, such as those in the aerospace and automotive industry in which the mechanical response must be optimised. Many of these applications are subjected to high rate or impact loading, yet it is believed that there is no prior research on the strain rate dependence in these materials. This research investigates the effect of strain rate and laser energy density on laser sintered polyamide 12. In the study presented here, parts produced using four different laser sintered energy densities were exposed to uniaxial compression tests at strain rates ranging from 10−3 to 10+3 s−1 at room temperature, and the dependence on these parameters is presented

Dynamic behaviour of silks: Nature’s precision nanocomposites

Silk is often cited as a material worth imitating, due to its high strength and toughness. In order to produce a synthetic analogue, or enhanced natural version, the microstructural basis of these properties must be understood. Current understanding is that silk deforms through the detachment of nano-scale crystallites, in the manner of a damaged composite. This picture forms the basis for constitutive models, but validation data is limited to low strain-rates. Here we present a programme of research in which high-rate behaviour is studied through ballistic impact experiments. These have been applied to the silk of the Bombyx mori moth, as harvested from cocoons, and to the major ampullate thread of the golden orb weaver spider Nephila edulis. Longitudinal wave-speeds, and air drag coefficients, have been calculated for selected cases. Differences between the response of various silks and a similar synthetic fibre, nylon, are discussed, and future plans are presented

Dynamic behaviour of silks: Nature’s precision nanocomposites

Silk is often cited as a material worth imitating, due to its high strength and toughness. In order to produce a synthetic analogue, or enhanced natural version, the microstructural basis of these properties must be understood. Current understanding is that silk deforms through the detachment of nano-scale crystallites, in the manner of a damaged composite. This picture forms the basis for constitutive models, but validation data is limited to low strain-rates. Here we present a programme of research in which high-rate behaviour is studied through ballistic impact experiments. These have been applied to the silk of the Bombyx mori moth, as harvested from cocoons, and to the major ampullate thread of the golden orb weaver spider Nephila edulis. Longitudinal wave-speeds, and air drag coefficients, have been calculated for selected cases. Differences between the response of various silks and a similar synthetic fibre, nylon, are discussed, and future plans are presented

What is binding? An examination of the bond of marriage in face of the pastoral crisis of broken marriages in the Catholic Church in England and Wales

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN013651 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Mechanical behaviour of polymers at high rates of strain

The stress-strain behaviours of polycarbonate (PC) and polyvinylidene difluoride (PVDF) have been measured over a range of strain rates at room temperature and a range of temperatures at high strain rate. Both materials show an approximately bilinear dependence of yield stress on strain rate over the rates examined. The experiments at different temperatures allow the high strain rate glass and $\beta$ transitions to be identified in PC, and the melting point and glass transition to be identified in PVDF. These can be confirmed by comparison to Dynamic Mechanical Analysis (DMA) measurements on the materials. Applying a time-temperature superposition to the data shows that these transitions are the cause of the bilinearity in the strain rate dependence of the materials. The behaviour of nominal (or engineering) stress in PC is also examined

Deformation behaviour of stainless steel microlattice structures by selective laser melting

Recent developments in selective laser melting (SLM) have enabled the fabrication of microlattice structures with periodic unit cells: a potential sandwich core material for energy dissipation. In this study, a full scale 3D finite element (FE) model was developed to investigate the macroscopic deformation of microlattice structures and the microscopic stress and strain evolution in the solid struts of the microlattice. The constitutive behaviour of SLM stainless steel 316L, the parent material of microlattice, was accurately characterised using non-contacting imaging techniques and input to the developed FE model, which was then validated by uniaxial compression experiments. It was found that local plastic stress and strain evolve near the nodal joint, thus forming a plastic hinge, whilst the majority of the strut remains elastic. The localised plastic stress/strain and the volume of plastic zone increase with the compression of the microlattice, resulting in the nearly plateau region with slight linear hardening in the stress−strain curve. The final densification process is dominated by the self-contact interaction among struts in the microlattice. Finally, the FE predictions reveal that the deformation of a microlattice is significantly affected by applied boundary conditions and constitutive properties of SLM parent materials such as Young׳s modulus

Experimental characterisation of the strain rate dependent failure and damage behaviour of 3D composites

Two through-thickness angle-interlock (TTAIL) 3D weaves especially designed to minimise crimp and with different binder volume fraction (3% and 6%), but otherwise identical architecture, have been characterised at quasi-static and dynamic loading. The aim of this work was to assess the suitability of different experimental techniques to investigate the effect of through thickness reinforcement on failure and damage behaviour of thin 3D reinforced composite plates, providing data that ultimately can be used to validate a numerical modelling strategy. It was found that there was little difference between the materials in terms of in-plane properties; however, the impact resistance of the 6% material was significantly increased. Furthermore, a noticeable difference between the interlaminar shear behaviour in warp and weft direction was observed. Therefore, it can be concluded that for a given weave architecture, a higher binder tow size (in this case 6%) can be used without compromising the in-plane response