Abstract
A wide variety of hyperelastic rubber-like materials, exhibiting strong nonlinear stress–strain relations under large deformations, is applied in various industrial mechanical systems and engineering applications involving shock and vibration absorbers. An optimal design procedure of an elevator chassis crashing on a hyperelastic shock absorber in a fail scenario, applicable in large-scale mechanical systems or industrial structures of high importance under strong nonlinear dynamic excitation, is presented in this work. For the characterization of the hyperelastic absorber, a Mooney–Rivlin material model was adopted, and a series of in-lab compression quasi-static tests were conducted. Applying a fully parallelizable state-of-the-art stochastic model updating methodology, coupled with robust, accurate and efficient Finite Element Analysis (FEA) software, the hyperelastic behavior of the shock absorber was validated under uniaxial large deformation, in order to tune all material parameters and develop a high-fidelity FE model of the shock absorber system. Next, a series of in situ full-scale experimental trials were carried out using a test-case elevator chassis, representing the crash scenario on the buffer absorber system, after a controlled free fall. A limited number of sensors, i.e., triaxial accelerometers and strain gauges, were placed at characteristic points of the real structure of the elevator chassis recording experimental data. A discrete Finite Element (FE) model of the experimentally tested arrangement involving the elevator chassis and updated buffer absorber system along with all boundary conditions was developed and used in explicit nonlinear analysis of the crash scenario. Steel material properties and the characterized updated Mooney–Rivlin material model were assigned to the elevator chassis and buffer, respectively. A direct comparison of the numerical and experimental data validated the reliability and accuracy of the methodology applied, whereas results of the analysis were used in order to redesign and optimize a new-design elevator chassis, achieving minimum design stresses and satisfying serviceability limit states.
Highlights
The advancement of technology in new rubber-like elastomer materials, exhibiting strong nonlinear stress–strain relations under large deformations, has increased in recent years and gained the attention of researchers in the area of continuum mechanics, leading to the development of products and applications implemented in various industrial mechanical systems and engineering problems involving shock and vibration absorbers
Compared to computationally faster gradientfree local optimizers such as Nelder-Mead simplex direct search algorithm available in MATLAB fminsearch function, CMA-evolutionary strategies (ES) is suitable in finding the global optimum, avoiding being trapped at local optima, and has demonstrated rapid convergence capabilities, when searching for a global optimum compared to other evolution algorithms
The phenomenon known as the Mullins effect [28,29], where the softening of the stress–strain curve of the examined rubber-like material depends on the sequence and level of eaIc1h=loλa1d2 i+ngλ2c2y+cleλ,32is not considered
Summary
The advancement of technology in new rubber-like elastomer materials, exhibiting strong nonlinear stress–strain relations under large deformations, has increased in recent years and gained the attention of researchers in the area of continuum mechanics, leading to the development of products and applications implemented in various industrial mechanical systems and engineering problems involving shock and vibration absorbers. The material properties of the specific polyurethane elastomer shock absorber structure are classified and tuned reconciling experimental data to equivalent numerical (FE) model computations This is achieved using residuals based on the experimental and numerical time histories of displacements [11,12]. Combining results from an in-lab experimental arrangement involving the unknown part, along with the implementation of the above computational tool, the mechanical characteristics and material properties of the applied elastomer were tuned and validated, developing a high-fidelity FEM model of the shock absorber. Parameter estimation is based on response time history measurements of displacements This formulation has the advantage of applicability over both linear and non-linear systems; it compares the measured raw data of the experimental arrangement to the equivalent predictions of the numerical model. It is worthwhile to mention that during the experimental measurements, the loading under which the buffer is excited is recorded, and the displacement responses and the measured force is introduced as excitation in the FE model
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