Vladislav Laš

Progressive Damage of Unidirectional Composite Panels

This work focuses on the numerical simulation of damage and fracture of unidirectional fiber-reinforced composite structures using the finite element method. A computational model is presented which can predict initial failure and is capable of the simulation of the subsequent process of local material damage up to final fracture. This procedure also known as progressive failure analysis originally combines Pucks failure criterion for the prediction of local failure and an innovative stiffness degradation approach for the simulation of resulting damage. The performance of the proposed model is demonstrated on examples of tensile tests of single-ply fiber-reinforced panels having different fiber orientations with and without stress concentrators. The numerical simulation is performed both as quasi-static and transient analysis and it involves identification and repetitive adjustment of material properties. The comparison of the results from experiment and from the simulation yields satisfactory agreement.

Improved nonlinear stress-strain relation for carbon-epoxy composites and identification of material parameters

This study focuses on the comparison of selected nonlinear stress—strain relations for unidirectional continuous fiber carbon—epoxy composites and the identification of their parameters under tensile loading. Simple tensile tests of thin strips with various fiber orientations are performed. One linear relation, two types of nonlinear stress—strain relations taken from literature, and one improved relation are analyzed and used within the identification process. All the relationships are deduced from polynomial expansion of complementary energy density. The process, using a combination of the mathematical optimization method and finite element analysis, is described with the necessary details. Failure analysis for the determination of the first failure using Puck’s action plane concept is also performed. The tensile and shear strengths are investigated. The comparison of the results obtained from the identified material parameters with the results obtained using the material parameters given by manufacturer is included.

Experimental and Numerical Investigation of Response of Sandwich Composite Beam Subjected to Low-Velocity Impact

This paper deals with the progressive failure analysis of sandwich composite beam loaded with transversely low-velocity impact. A user defined material model was used for modeling of the non-linear orthotropic elastic behavior of composite skin. The non-linear behavior of foam core was modeled using Low-Density Foam material model. The numerical model was validated using performed experiment and the results in terms of deflection and contact force time dependencies are mutually compared.

Stress-Controlled Fatigue Testing of E-Glass Epoxy Composite: Monitoring of Micro-Damage

The paper deals with progressive and fatigue damage of long fiber E-glass epoxy composite, its residual stiffness degradation and corresponding transverse matrix crack density induced by load-controlled tension. Constant-amplitude fatigue tests in repeated tension of plain [±60]S; [±30]S; [0]8 and [0/902/±45/90]S samples were performed. Sudden onset of transverse matrix cracking and consequent gradual increase of its density has been observed in off-axis plies. The crack density increases with increasing number of cycles or load. Consequently, residual stiffness of the laminate decreases. It has been concluded that progressive/fatigue damage of the laminate is not a continuous homogenous process but the series of discrete sudden events emerging at ply level.

Numerical Simulation of the Impact on Wide Composite Sandwich Beam

This paper is focused on the development of a finite element model describing the behaviour of sandwich structure with composite skins and low density foam core in case of low-velocity transverse impact load. The material properties of foam core and composite skins were determined using tensile tests. The non-linear elastic behaviour of composite skins was implemented into the commercial finite elements software using material subroutine. The identification process combining finite element simulations and mathematical optimization method was used for the determination of material parameters of the composite skins. The foam core was modelled using Abaqus Low-density Foam material model considering the non-linear behaviour in case of tension.