Phuong Tran

Three-dimensional modelling of auxetic sandwich panels for localised impact resistance

Sandwich panels with auxetic lattice cores confined between metallic facets are proposed for localised impact resistance applications. Their performance under localised impact is numerically studied, considering the rate-dependent effects. The behaviour of the composite structure material at high strain rates is modelled with the Johnson-Cook model. Parametric analyses are conducted to assess the performance of different designs of the hybrid composite structures. The results are compared with monolithic panels of equivalent areal mass and material in terms of deformations and plastic energy dissipation. Design parameters considered for the parametric analyses include the auxetic unit cell effective Poisson’s ratio, thickness of the facet, material properties and radius of the unit cell’s struts. Significant reduction in computational time is achieved by modelling a quarter of the panel, with shell elements for facets and beam elements for the auxetic core. With projectile impacts up to 200 m/s, the auxetic composite panels are found to be able to absorb a similar amount of energy through plastic deformation, while the maximum back facet displacements are reduced up to 56% due to localised densification and plastic deformation of the auxetic core.

Effects of architecture on ballistic resistance of textile fabrics: Numerical study:

Composite textiles composed of materials such as Kevlar, Dyneema and Zylon are extensively used in many force/impact protection applications, such as body armor, and automobile and airplane engine fragment resistant containment. Significant effort has been devoted to ballistic testing of composite fabrics made from various manufacturing processes and designs. Performing comprehensive ballistic and impact tests for these composite textiles is a very time-consuming and costly task. Numerical models are presented in this research, thereby providing predictive capability for the manufacturer and designer to minimize field testing, as well as shedding light on to the damage mechanisms of composite fabrics subjected to ballistic impact. Several representative composite fabric architectures (such as plain weave, basket weave and knitted fabrics) are generated for finite element analysis. Numerical investigation is conducted on these fabric structures of the same mass per unit area subjected to projectile impacts. Failure patterns of woven and knitted fabrics obtained from numerical simulations are compared with those observed experimentally. Performances of the representative textile structures are evaluated based on the resultant velocity of the projectile, as well as various energy components. The influences of yarn–yarn and yarn–projectile friction properties on the ballistic performance of various textile structures are presented. To highlight the effects of projectile geometry and angular rotation on the fracture of woven and knitted fabrics, a series of simulations are also performed with three distinctive projectiles of the same mass and impact energy.

Dynamic delamination of patterned thin films

We investigate laser-induced dynamic delamination of a patterned thin film on a substrate. Controlled delamination results from our insertion of a weak adhesion region beneath the film. The inertial forces acting on the weakly bonded portion of the film lead to stable propagation of a crack along the film/substrate interface. Through a simple energy balance, we extract the critical energy for interfacial failure, a quantity that is difficult and sometimes impossible to characterize by more conventional methods for many thin film/substrate combinations.

Comparison of dynamic and quasi-static measurements of thin film adhesion

Adhesive failure and the attendant delamination of a thin film on a substrate is controlled by the fracture energy required to propagate a crack along the interface. Numerous testing protocols have been introduced to characterize this critical property, but are limited by difficulties associated with applying precise loads, introducing well-defined pre-cracks, tedious sample preparation and complex analysis of plastic deformation in the films. The quasi-static four-point bend test is widely accepted in the microelectronics industry as the standard for measuring adhesion properties for a range of multilayer thin film systems. Dynamic delamination methods, which use laser-induced stress waves to rapidly load the thin film interface, have recently been offered as an alternative method for extracting interfacial fracture energy. In this work, the interfacial fracture energy of an aluminium (Al) thin film on a silicon (Si) substrate is determined for a range of dynamic loading conditions and compared with values measured under quasi-static conditions in a four-point bend test. Controlled dynamic delamination of the Al/Si interface is achieved by efficient conversion of the kinetic energy associated with a laser-induced stress wave into fracture energy. By varying the laser fluence, the fracture energy is investigated over a range of stress pulse amplitudes and velocities. For lower amplitudes of the stress wave, the fracture energy is nearly constant and compares favourably with the critical fracture energy obtained using the four-point bend technique, about 2.5 J m−2. As the pulse amplitude increases, however, a rate dependence of the dynamic fracture energy is observed. The fracture energy increases almost linearly with pulse amplitude until reaching a plateau value of about 6.0 J m−2.

Nonlinear dynamic response and vibration of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) shear deformable plates with temperature-dependent material properties and surrounded on elastic foundations

ABSTRACT Based on Reddy’s third-order shear deformation plate theory, the nonlinear dynamic response and vibration of imperfect functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates on elastic foundations subjected to dynamic loads and temperature are presented. The plates are reinforced by single-walled carbon nanotubes which vary according to the linear functions of the plate thickness. The plate’s effective material properties are assumed to depend on temperature and estimated through the rule of mixture. By applying the Airy stress function, Galerkin method and fourth-order Runge–Kutta method, nonlinear dynamic response and natural frequency for imperfect FG-CNTRC plates are determined. In numerical results, the influences of geometrical parameters, elastic foundations, initial imperfection, dynamic loads, temperature increment, and nanotube volume fraction on the nonlinear vibration of FG-CNTRC plates are investigated. The obtained results are validated by comparing with those of other authors.

Nonlinear dynamic response and vibration of imperfect shear deformable functionally graded plates subjected to blast and thermal loads

ABSTRACT Based on Reddys higher-order shear deformation plate theory, this article presents an analysis of the nonlinear dynamic response and vibration of imperfect functionally graded material (FGM) thick plates subjected to blast and thermal loads resting on elastic foundations. The material properties are assumed to be temperature-dependent and graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. Numerical results for the dynamic response and vibration of the FGM plates with two cases of boundary conditions are obtained by the Galerkin method and fourth-order Runge–Kutta method. The results show the effects of geometrical parameters, material properties, imperfections, temperature increment, elastic foundations, and boundary conditions on the nonlinear dynamic response and vibration of FGM plates.

Nonlinear vibration and dynamic response of imperfect eccentrically stiffened shear deformable sandwich plate with functionally graded material in thermal environment

This paper presents an analytical approach to investigate the nonlinear dynamic response and vibration of shear deformable imperfect eccentrically stiffened sandwich plate with functionally graded material (FGM) on elastic foundation using both of the first-order shear deformation plate theory and stress function with full motion equations (not using Volmirs assumptions). The thick sandwich plates are assumed to rest on elastic foundation and subjected to mechanical loads in thermal environment. Numerical results for dynamic response of the eccentrically stiffened thick sandwich plates are obtained by Runge–Kutta method. The results show the influences of geometrical parameters, material properties, imperfections, the elastic foundations, eccentric stiffeners, mechanical loads and temperature on the nonlinear dynamic response and nonlinear vibration of functionally graded sandwich plates. The numerical results in this paper are compared with the results reported in other publications.

Composite Materials for Next Generation Building Façade Systems

Composite materials, such as glass fibre reinforced polymers (GFRPs), possess the advantages of high strength and stiffness, low density, as well as manufacturing flexibility; therefore, their potential in replacing conventional materials (such as concrete, aluminium and steel) in building construction has become attractive. One of the major issues that hinder the extensive use of composite structures in high-rise building technology is related to their fire resistance performance. Significant efforts have been devoted to develop better material systems and composite manufacturing technologies to comply with various building construction safety codes, while maintaining the architectural aesthetic appeal. This paper presents the potential use of fibre reinforced polymer composites (FRPCs) in modern facade systems, with a special focus on their fire performance. A case study relating to the fire performance of glass fibre reinforced polymers is also presented. This case study is based on the numerical model established for glass fibre reinforced polyester, vinyl ester, epoxy and phenol without flame retardants.

Impact Resistance and Failure Analysis of Plain Woven Curtains

Blast and impact-resistant curtains are increasingly utilized for various applications in critical infrastructures to retrofit or enhance energy absorption and fragments capturing capabilities. Investigation of the impact resistance and failure mechanisms of the protective curtains are therefore critical. Understanding the energy absorption and failure mechanisms of fabrics impacted by potential debris of medium to low striking speeds could thus lead to improvements in designing spall linings system as well as bullet-proof combat uniforms against fragmentations. This paper aims at investigating the deformation and damage mechanisms of woven fabrics subjected to low velocity impact. Gas-gun experiments are conducted to investigate the ballistic resistance of the fabrics. A mesoscale modelling approach is developed and validated with the experiment to simulate the ballistic events for various projectile striking velocities ranging between 50–150 m/s. Parametric studies and comparisons are then carried out to examine the primary energy components: strain, kinetic, and friction energy, and their associated distribution within the fabric. The decoupling of the energy absorbed by the fabric provides an insight into the interaction of the yarns, as well as the significance of the energy components during the different stages of the impact event. The studies suggest the importance of the inter-yarn friction in a low speed impact scenario.

Effect of Textile Architecture on Energy Absorption of Woven Fabrics Subjected to Ballistic Impact

Woven fabrics are widely used in various protective applications. The effects of different woven architectures (such as plain, basket, twill and satin) on impact resistance performance have not been adequately studied. In this work, high-speed impact testing on single layer plain weave structures has been carried out using a gas gun experimental setup. Ballistic resistance performance of the woven fabric is evaluated based on the resultant velocity of the projectile, as well as the post-mortem failure analysis. Finite element computational models are presented in this research, thereby providing predictive capability for the manufacturer and designer in order to minimise field testing, as well as shedding light on to the damage mechanisms of composite fabrics subjected to ballistic impact. The numerical model is validated with the experimental results in terms of dissipated energy and resultant velocity. Numerical investigation is conducted on other woven structures of identical areal density for comparison, revealing the importance of fabric architecture. The influences of yarn-yarn and yarn-projectile friction properties on the ballistic performance of various textile structures are also presented.