Contact force history and dynamic response due to the impact of a soft projectile

A series of ballistic impact tests on several different instrumented targets was performed to characterize the dynamic contact force history resulting from the impact of a compliant projectile. The results show that the variation of contact force history with impact velocity does not follow the trends predicted by classical impact models. An empirical model was therefore developed to describe this behavior. This model was then used in a finite-element analysis to estimate the force history and calculate the resulting dynamic strain response in a transversely impacted composite laminate

The distribution of asteroids: evidence from Antarctic micrometeorites

The relative abundances of types amongst 550 AMMs are reported. These suggest that C-type asteroids vary from petrologic type 1 to 3.2 and that the majority of S-type asteroids are chondrule-rich

A High-Order Kernel Method for Diffusion and Reaction-Diffusion Equations on Surfaces

In this paper we present a high-order kernel method for numerically solving diffusion and reaction-diffusion partial differential equations (PDEs) on smooth, closed surfaces embedded in $\mathbb{R}^d$. For two-dimensional surfaces embedded in $\mathbb{R}^3$, these types of problems have received growing interest in biology, chemistry, and computer graphics to model such things as diffusion of chemicals on biological cells or membranes, pattern formations in biology, nonlinear chemical oscillators in excitable media, and texture mappings. Our kernel method is based on radial basis functions (RBFs) and uses a semi-discrete approach (or the method-of-lines) in which the surface derivative operators that appear in the PDEs are approximated using collocation. The method only requires nodes at "scattered" locations on the surface and the corresponding normal vectors to the surface. Additionally, it does not rely on any surface-based metrics and avoids any intrinsic coordinate systems, and thus does not suffer from any coordinate distortions or singularities. We provide error estimates for the kernel-based approximate surface derivative operators and numerically study the accuracy and stability of the method. Applications to different non-linear systems of PDEs that arise in biology and chemistry are also presented

Dynamic delamination crack propagation in a graphite/epoxy laminate

Dynamic delamination crack propagation in a (90/0) 5s Graphite/Epoxy laminate with an embedded interfacial crack was investigated experimentally using high speed photography. The dynamic motion was produced by impacting the beamlike laminate specimen with a silicon rubber ball. The threshold impact velocities required to initiate dynamic crack propagation in laminates with varying initial crack positions were determined. The crack propagation speeds were estimated from the photographs. Results show that the through the thickness position of the embedded crack can significantly affect the dominant mechanism and the threshold impact velocity for the onset of crack movement. If the initial delamination is placed near the top of bottom surface of the laminate, local buckling of the delaminated plies may cause instability of the crack. If the initial delamination lies on the midplane, local buckling does not occur and the initiation of crack propagation appears to be dominated by Mode II fracture. The crack propagation and arrest observed was seen to be affected by wave motion within the delamination region

A High-Order Radial Basis Function (RBF) Leray Projection Method for the Solution of the Incompressible Unsteady Stokes Equations

A new projection method based on radial basis functions (RBFs) is presented for discretizing the incompressible unsteady Stokes equations in irregular geometries. The novelty of the method comes from the application of a new technique for computing the Leray-Helmholtz projection of a vector field using generalized interpolation with divergence-free and curl-free RBFs. Unlike traditional projection methods, this new method enables matching both tangential and normal components of divergence-free vector fields on the domain boundary. This allows incompressibility of the velocity field to be enforced without any time-splitting or pressure boundary conditions. Spatial derivatives are approximated using collocation with global RBFs so that the method only requires samples of the field at (possibly scattered) nodes over the domain. Numerical results are presented demonstrating high-order convergence in both space (between 5th and 6th order) and time (up to 4th order) for some model problems in two dimensional irregular geometries.Comment: 34 pages, 8 figure

Microbial D/H fractionation in extraterrestrial materials: application to micrometeorites and Mars

High D/H terrestrial alteration of micrometeorites is described and suggested to be a result of microbial isotopic fractionation by methanogens. Applications to other planetary materials, including martian meteorites, are also considered

Gendering Pensions: Making Women Visible

This paper argues that the UK pension system is gender blind and is structured around a heteropatriarchal experience. It does so by analysing two key pieces of UK pension policy: the New Flat Rate State Pension and Auto-Enrolment. Since the 1980s the value of the British state pension has fallen, and it is now worth half what it was in 1979. This presents a particular disadvantage for women who not only tend to be lower paid, but because of a gendered occupational life course, also tend to work part-time hours, and thus also fail to work the number of qualifying years for the full state pension. Traditionally, this results in a pension penalty for women. It is argued that the New Flat Rate State Pension and Auto-Enrolment will counteract this disadvantage, and political discourses used by policymakers claim that they will also create a fairer society. The argument presented here seeks to demonstrate that this claim is problematic by exposing how (i) gender blindness prevents gender equality in pension provision delivery, and (ii) how the formulation of these policies are actually reinforced by a heteropatriarchal welfare system, which fundamentally undermines the contribution made by women to the economy