Stochastic flexural buckling response of thin-walled composite strips

Thin-walled composite structures are susceptible to undergo buckling leading to undesirable structural integrity problems. This paper proposes an efficient modeling approach for determining the axial critical buckling load-carrying capacities of thin-walled composite strips. Taking advantage of the inherent geometrical features of a strip, it is modeled as a one-dimensional structure. The reduced one-dimensional (1D) strip model is developed by using the Variational Asymptotic Method (VAM). In this mathematical framework, the original 3D problem is separated into a 2D cross-section and a 1D problem along the span of the strip. Although the methodology readily provides 2D nonlinear cross-sectional stiffness, in this work we have restricted the analysis to only a linear problem. While the cross-sectional stiffness is determined analytically, the 1D prob lem is solved numerically to determine the critical buckling load using the finite element method. The buckling load results obtained from this model are validated with analytical and experimental results reported in the literature. The proposed model in this paper takes into account the non-classical parameters of the composite strip due to its inherent structural coupling properties, anisotropy, and complex geometrical attributes. Detailed parametric studies have been carried out to investigate the influence of the boundary conditions, ply angle variations, and different aspect ratios of the composite strips. The methodology is then extended to take into consideration the stochastic effects due to uncertain material proper ties at the constituent levels. The influence of these uncertainties is presented in the form of stochastic distribution of buckling load by adopting a probabilistic modeling approach. The stochastic response of delaminated composite strips is also analyzed. The stochastic distribution shows a wider response bound of critical buckling load. The presented study on the buckling behavior of healthy and delaminated thin-walled rectangular cross-section composite strips facilitates an exploration of structural stability in the presence of intricate geometric characteristics and variable material properties inherent to these composite strips

Daksha: On Alert for High Energy Transients

We present Daksha, a proposed high energy transients mission for the study of electromagnetic counterparts of gravitational wave sources, and gamma ray bursts. Daksha will comprise of two satellites in low earth equatorial orbits, on opposite sides of earth. Each satellite will carry three types of detectors to cover the entire sky in an energy range from 1 keV to >1 MeV. Any transients detected on-board will be announced publicly within minutes of discovery. All photon data will be downloaded in ground station passes to obtain source positions, spectra, and light curves. In addition, Daksha will address a wide range of science cases including monitoring X-ray pulsars, studies of magnetars, solar flares, searches for fast radio burst counterparts, routine monitoring of bright persistent high energy sources, terrestrial gamma-ray flashes, and probing primordial black hole abundances through lensing. In this paper, we discuss the technical capabilities of Daksha, while the detailed science case is discussed in a separate paper

The in-situ mechanical testing of nanoscale single-crystalline nanopillars

This article reviews recent studies on the mechanical properties of cylindrical metallic nanopillars subjected to uniaxial deformation. Remarkable strengths and very different mechanical properties arise due to the activation of unique deformation mechanisms operating in these nanoscale volumes. Effects of both size and microstructure are discussed