Robert Zemčík

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.

Stereophotogrammetry of the perineum during vaginal delivery.

To analyze deformation of the perineum during normal vaginal delivery in order to identify clinical steps that might be beneficial when executing manual perineal protection.

High-Performance 4-Node Shell Element with Piezoelectric Coupling

The paper focuses on the topic of smart and adaptive structures using embedded piezoelectric sensors and actuators. A new high-performance degenerated continuum based solid piezoelectric shell element is developed herein. It is an isoparametric 4-noded quadrilateral layered element based on the Reissner-Mindlin theory of plates with piezoelectric coupling. It assumes linear elasticity and small displacements, rotations and strains theories. The element is free of both membrane and transverse shear locking effects, and it has fully ranked stiffness matrix. This is ensured by a carefully selected combination of the Enhanced Assumed Strain, Discrete Shear Gap, and Drilling Rotations approaches. The element was implemented into ANSYS 7.1 and named SHELL10X. The pure-mechanical and static behavior is tested, e.g., using the standard set of test problems—patch tests—proposed by Harder and MacNeal. Furthermore, an experimental measurement has been carried out on a steel beam with applied piezoelectric patches. The harmonic response of the beam was studied to test the piezoelectric behavior and to show the reliability of the element. Good agreement between the measured and calculated data was achieved.

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.

Experimental Identification of Material Properties of Piezoelectric Patch Transducer

This work is focused on identification of material properties of piezoelectric patch transducers used e.g. for structural health monitoring before attaching to the substrate structure. Two experimental methods were concerned. At first two piezoelectric patches were supplied with a pair of collocated strain gauge rosettes. Both transducers were actuated with the same periodical signal. Significant difference in the results for two transducers was found, however it was claimed to be within tolerance by the producer. As an alternative method a measurement in an optical microscope was chosen. The patch was clamped at one side and actuated by a voltage signal. The displacement of the free end was captured by the microscope and processed in a graphical editor. Finally, a finite element model of the transducer was created and its material data were obtained by calibration with experimental data.

Strength Analysis of Carbon Fiber-reinforced Plastic Coupling for Tensile and Compressive Loading Transmission

The design and production of high strength composite/metal joint is generally a challenging task. This work focuses on joints that can be produced using filament winding technology. The main principle in this case is that the fibers of the composite are wrapped directly around the shape of a metal component, for example a pin. It allows the creation of a joint, where the load is transferred directly from the metal part into the composite structure without cutting fibers. Therefore, high performance in strength can be achieved. The composite part of the joint can also constitute flexible coupling between two metal components. The investigation of mechanical behavior of a carbon fiber-reinforced plastic coupling under tension, compression, and bending is carried out. Performed experiments are compared with three-dimensional finite element simulations where adjusted LaRC04 failure criterion is used. The influence of the coupling concept and its geometry on the joint strength is investigated.