Characterising delamination in composite materials : a combined genetic algorithm - finite element approach

A novel delamination identification technique based on a low-population genetic algorithm for the quantitative characterisation of a single delamination in composite laminated panels is developed, and validated experimentally The damage identification method is formulated as an inverse problem through which system parameters are identified. The input of the inverse problem, the central geometric moments (CGM), is calculated from the surface out-of-plane displacements measurements of a delaminated panel obtained from Digital Speckle Pattern Interferometry (DSPI). The output parameters, the planar location, size and depth of the flaw, are the solution to the inverse problem to characterise an idealised elliptical flaw. The inverse problem is then reduced to an optimisation problem where the objective function is defined as the L2 norm of the difference between the CGM obtained from a finite element (FE) model with a trial delamination and the moments computed from the DSPI measurements. The optimum crack parameters are found by minimising the objective function through the use of a low-population real-coded genetic algorithm (LARGA). DSPI measurements of ten delaminated T700/LTM-45EL carbon/epoxy laminate panels with embedded delaminations are used to validate the methodology presented in this thesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Determination of constitutive parameters from a Taylor test using inverse analysis

Identification of material constitutive parameters is critical for accurate representation of the mechanical behavior of materials at high strain rates. However, customary characterization procedures based on curve fitting of stress-strain curves, in some cases, are not accurate when the mechanical response exhibits strain rate dependency. In this paper, an inverse characterization technique based on the Taylor impact test is proposed. The technique uses a data reduction operator based on line moments and genetic algorithm optimization to determine the optimum constitutive parameters. Material parameters for a low carbon steel associated with the Plastic Kinematic model were determined using the proposed method.La identificación de los parámetros constitutivos del material es fundamental para representar con precisión el comportamiento mecánico de los materiales a altas velocidades de deformación. Sin embargo, los procedimientos habituales de caracterización basados en el ajuste de curvas de tensión-deformación, en algunos casos, no son precisos cuando la respuesta mecánica presenta dependencia de la velocidad de deformación. En este trabajo se propone una técnica de caracterización inversa basada en el ensayo de impacto de Taylor. La técnica utiliza un operador de reducción de datos basado en momentos de línea y la optimización mediante algoritmos genéticos para determinar los parámetros constitutivos óptimos. Mediante el método propuesto se determinaron los parámetros del material para un acero de bajo carbono asociados al modelo cinemático plástico

Material model for modeling clay at high strain rates

Modeling clay is a soft malleable material made from oils and waxes. This material is fundamental for ballistic evaluation of body armors because it is used as backing material in ballistic tests. After a ballistic impact, a back-face indentation is measured to assess performance of the armor. Due to the important role of modeling clay in this particular application, its mechanical characterization and comprehension of penetration mechanics are essential for development of new personal protection systems. This paper presents a two-step computational methodology to calibrate parameters of a Cowper-Symonds material model for modeling clay at characteristic strain rates up to 1.8×104 s-1. In the first stage, a high-speed camera is used to record the penetration of a gas-gun launched cylindrical mass with a hemispherical cap into a block of clay. Image-processing software is used to capture the tail of the projectile as it penetrates into the clay. These data are then used to sample the penetration depth as function of time. In the second stage, an in-house developed model of penetration, based on both the spherical cavity expansion theory and the Tate penetration equation, is used to determine, by inverse analysis, the parameters of the Cowper-Symonds clay model. The proposed constitutive relationship for clay and the determined material parameters can be applied accurately to problems involving high strain rates

Behavior Of Oil-based Modeling Clay At Medium Strain Rates

The modeling clay is an oil-based soft, flowable, and pliable material made from waxes and oils. Besides its primary use for making sculptures, the modeling clay is commonly used to evaluate bulletproof vests and simulate metal manufacturing processes by conformation. In ballistic tests, the clay is used to retain the deformation of the rear face of body armors; and in the study of metal forming processes, it is used as a physical model to provide information on the plastic flow. However, its mechanical dynamic behavior is not entirely understood. In this study, Plastilina Roma No. 1 modeling clay was mechanically characterized using the power-law constitutive model at medium strain rates (Formula presented.). The material parameters were determined using a penetration model based on the Cavity Expansion Theory and an inverse technique involving the comparison of the model with experimentation. The optimum set of constitutive parameters was found by reducing the difference of the calculated penetration profile and the measurements from a drop test. This optimization process was programmed on the MATLAB–Simulink environment. The determined material parameters were validated by comparing the results from a computational model with three test set-ups. Finite element model results show good concordance with experimental measurements

The Response of Manicaria saccifera Natural Fabric Reinforced PLA Composites to Impact by Fragment Simulating Projectiles

This chapter presents the impact behavior of a recently developed green composite material made of Manicaria saccifera natural fabric reinforced Poly-Lactic Acid (PLA). Composite coupons made of PLA and Manicaria saccifera fabric were produced by compression molding using the film stacking method. The composite ballistic limit (V50) was determined by subjecting PLA/Manicaria coupons, of varying lay-ups and thicknesses, to ballistic impact loading using fragment simulating projectiles (FSPs) according to the MIL-STD-662F standard. It was found that coupons with areal densities between 0.2 and 0.3 g/cm2 displayed a V50 between 50 and 70 m/s. Also, it was found that the V50 increased nonlinearly as a function of coupon thickness, but it does not depend on the composite stacking sequence. Finally, the energy absorbed by the material at impact on complete penetrations is uniform and independent of the striking velocity, whereas for partial penetrations increases exponentially.En este capítulo se presenta el comportamiento ante el impacto de un material compuesto ecológico recientemente desarrollado a base de tejido natural de Manicaria saccifera reforzado con ácido poliláctico (PLA). Los cupones de material compuesto hechos de PLA y tejido de Manicaria saccifera se produjeron mediante moldeo por compresión utilizando el método de apilamiento de películas. El límite balístico del material compuesto (V50) se determinó sometiendo los cupones de PLA/Manicaria, de distintas composiciones y espesores, a cargas de impacto balístico utilizando proyectiles de simulación de fragmentos (FSP) de acuerdo con la norma MIL-STD-662F. Se comprobó que los cupones con densidades de área entre 0,2 y 0,3 g/cm2 mostraban una V50 entre 50 y 70 m/s. Además, se comprobó que el V50 aumentaba de forma no lineal en función del grosor del cupón, pero no depende de la secuencia de apilamiento del material compuesto. Por último, la energía absorbida por el material en el momento del impacto en las penetraciones completas es uniforme e independiente de la velocidad de impacto, mientras que en las penetraciones parciales aumenta exponencialmente

Development and Characterization of Rice Husk and Recycled Polypropylene Composite Filaments for 3D Printing

Nowadays the use of natural fiber composites has gained significant interest due to their low density, high availability, and low cost. The present study explores the development of sustainable 3D printing filaments based on rice husk (RH), an agricultural residue, and recycled polypropylene (rPP) and the influence of fiber weight ratio on physical, thermal, mechanical, and morphological properties of 3D printing parts. Thermogravimetric analysis revealed that the composite’s degradation process started earlier than for the neat rPP due to the lignocellulosic fiber components. Mechanical tests showed that tensile strength increased when using a raster angle of 0° than specimens printed at 90°, due to the weaker inter-layer bonding compared to in-layer. Furthermore, inter layer bonding tensile strength was similar for all tested materials. Scanning electron microscope (SEM) images revealed the limited interaction between the untreated fiber and matrix, which led to reduced tensile properties. However, during the printing process, composites presented lower warping than printed neat rPP. Thus, 3D printable ecofriendly natural fiber composite filaments with low density and low cost can be developed and used for 3D printing applications, contributing to reduce the impact of plastic and agricultural waste

Bioactive Poly(lactic acid)–Cocoa Bean Shell Composites for Biomaterial Formulation: Preparation and Preliminary In Vitro Characterization

The unique lignocellulosic and solvent-extractive chemical constituents of most natural fibers are rich in natural polymers and bioactive molecules that can be exploited for biomaterial formulation. However, although natural fibers’ main constituents have been already incorporated as material reinforcement and improve surface bioactivity of polymeric materials, the use of the whole natural fibers as bioactive fillers remains largely unexplored. Thus, we put forward the formulation of natural fiber filling and functionalization of biomaterials by studying the chemical composition of cocoa bean shells (CBS) and proposing the fabrication and characterization of polylactic acid (PLA) and CBS-based composite by solvent-casting. As was expected from previous studies of agro-industrial wastes, the main components of CBS were to cellulose (42.23 wt.%), lignin (22.68 wt.%), hemicellulose (14.73 wt.%), and solvent extractives (14.42 wt.%). Structural analysis (FTIR) confirms the absence of covalent bonding between materials. Thermal degradation profiles (DSC and TGA) showed similar mass losses and thermal-reaction profiles for lignocellulosic-fibers-based composites. The mechanical behavior of the PLA/CBS composite shows a stiffer material behavior than the pristine material. The cell viability of Vero cells in the presence of the composites was above 94%, and the hemolytic tendency was below 5%, while platelet aggregation increased up to 40%. Antioxidant activity was confirmed with comparable 2,2-diphe-277 nyl-1-picryl-hydrazyl-hydrate (DPPH) free-radical scavenging than Vitamin C even for PLA/CBS composite. Therefore, the present study elucidates the significant promise of CBS for bioactive functionalization in biomaterial-engineering, as the tested composite exhibited high biocompatibility and strong antioxidant activity and might induce angiogenic factors’ release. Moreover, we present an eco-friendly alternative to taking advantage of chocolate-industry by-products

The frequencies and molecular profiles of CD16+ monocyte subsets in patients with systemic lupus erythematosus, primary antiphospholipid syndrome and antiphospholipid syndrome with lupus, identify specific clinical features of these diseases

International audienc

The frequencies and molecular profiles of CD16+ monocyte subsets in patients with systemic lupus erythematosus, primary antiphospholipid syndrome and antiphospholipid syndrome with lupus, identify specific clinical features of these diseases

International audienc