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2 Journal of Achievements in Materials and Manufacturing Engineering

2 2009

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Simplified and advanced models of a valve system used in shock absorbers

Czop P., Sławik D., Śliwa P., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

2009

Vol. 33, nr 2

173-180

Purpose: The aim of this paper is to develop a model of a valve system applicable for strain and stress prediction. Design/methodology/approach: The analytical and numerical approaches are presented to provide an overview for available methods and prediction accuracy. Findings: An equivalent numerical model of a disc valve system of different complexity was developed and discussed. Research limitations/implications: It is important to provide a model functionality allowing for calculation of disc stacks supported by a coil spring and stack settings having the opening limiter. Disc stack stress and opening characteristics vs. applied pressure may be determined with simplified analytically derived model and full 2D model including almost all significant forces and moments in a stack of circular plates. An advantage of a simplified disc stack model is possibility of its implementation in an environment supporting matrix operations, e.g. Matlab. Practical implications: A valve system has to withstand the cyclic pressure load across the piston. The number of discs, their diameters and thicknesses directly affect durability of a valve system. Damper force and valve durability expressed in life-cycles are the optimization criteria considering during selection and tuning of a valve system. Originality/value: A new valve system was developed in two versions, i.e. simplified and advanced. The model allows durability prediction at the design stage reducing the testing costs of low-performance valve systems.

Experimental and numerical study of damage initiation mechanism in elastomeric composites

Silva Botelho T. D., Bayraktar E.

Journal of Achievements in Materials and Manufacturing Engineering

2009

Vol. 36, nr 1

65-70

Purpose: Experimental and Finite Element Analysis (FEA) of the damage initiation mechanisms in elastomeric composites were carried out under static loading at room temperature. Double Cantilever Beam (DCB) specimens from natural rubber (NR) vulcanised and reinforced with other materials such as carbon black, silica, fibres and textiles or metals (rubber composites). Design/methodology/approach: Very huge experimental results were compared with that of the Finite Element Analysis (FEA). Damage mechanism has been described with a threshold criterion to identify damage. The damage was evaluated just at the beginning of the tearing by assuming large strain. A typical type of specimen geometry of Double Cantilever Beam (DCB) specimens was considered under static tensile tests conducted on the notched specimens with variable depths. Findings: In this stage of this research, a finite element analysis (FEA) has been applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results. The numerical modelling is a representation of a previous experimental study. The specimen is stretched more than once its initial size, so that large strains occur. A hyper elastic Moonley-Rivlin law and a Griffith criterion are chosen. The finite elements analysis was performed with ABAQUS code (V.6.4.4). Practical implications: A damage criterion was suggested in the case of simple tension conditions by assuming large strain levels. an effective finite elements model has been developed to evaluate notch size effects on the load-displacement elastic response of 3D-DCB type specimen. Originality/value: This study proposes a threshold criterion for the damage just at the beginning of the tearing for Double Cantilever Beam (DCB) specimens from rubber composites and gives a detail discussion for explaining the damage mechanisms. Comparison of FEA results with those of experimental studies gives many facilities for the sake of simplicity in industrial applications.