Journal of Multiscale Modelling

Residual stresses and stress concentrations induced by impact-damage may shorten the fatigue life and cause premature failure of aeronautical components. Under cyclic loading, fatigue cracks may initiate at the points where high tensile stresses occur and propagate to failure. In this work, an experimentally validated finite element model was used to assess the stress state in impact-damaged 7075-T6 hourglass specimens subjected to rotating bending. In the first simulation step, the finite element method was used to model residual stresses in the specimens for various impact cases, with different masses of impacting objects and impact speeds and angles. In the subsequent simulation step, the damaged specimens were subjected to rotating bending. The total stresses in the impact region were obtained through the superposition of the residual stresses caused by the impact and the stresses due to the rotating bending load. The design of experiments was applied to the obtained finite element results to identify which impact parameters mostly influence the stress distribution in the damaged specimens. The analysis showed that the most significant parameter is the impact speed, followed by the material and the size of the impacting object while the influence of the impact angle is low.

The fatigue strength of components is affected by loading and environmental conditions, their geometry, the material and the manufacturing process adopted for their production. As a consequence of local stress concentrations, fatigue cracks can propagate to failure from the defects created by the manufacturing processes or introduced during the service life, as occurs in impact-damage. Ti6Al4V titanium alloy is commonly used in the aeronautical sector and other engineering applications due to its high specific strength. The study of the fatigue behavior of Ti6Al4V is therefore critical for designing reliable and durable structures. The work reports a synthesis of the results present in the literature for the fatigue behavior of Ti6Al4V in inert and aggressive environments, in the presence of a deposited coating, in the case of impact-damage, when components are produced by additive manufacturing and in the absence of solution treatment and over-aging.

The FE-based structural design of components made of rubber materials requires an experimental characterization to calibrate a proper hyperelastic material model. A strain energy density (SED) parameter is typically adopted to describe the hyperelastic behavior of isotropic rubbers. This can be written as a function of the strain tensors, the strain invariants or the stretch ratios and proper material parameters. The latter must be calibrated on experimental data generated by testing rubber materials under different loading conditions, typically two among uniaxial tension, pure shear and biaxial tension. In this context, the mechanical behavior of Ethylene–Propylene–Diene Monomer (EPDM) rubbers, both in the dense and expanded configurations, which are typically employed to manufacture automotive seals, has been investigated. First, uniaxial tension tests have been performed. Afterwards, a new fixture has been developed to perform equi-biaxial tension tests using a uniaxial testing machine. The fixture has been adopted to test EPDM cruciform specimens under equi-biaxial tension loading. Finally, both uniaxial and equi-biaxial data have been employed to fit a Mooney–Rivlin material model for each tested EPDM rubber, which has been validated by comparing the results of FE simulations with the experimental ones.

Modern planetary rovers are based on aluminum chassis, but thanks to carbon fiber composites, the weight of such mobility platforms can be dramatically lowered. This paper describes the design of a 6-wheeled rover with a rocker-bogie suspension, adopting carbon fiber laminates and short-fiber-reinforced polymers. This last feature is an innovative approach that fits well with the use of additive manufacturing, allowing for both highly optimized parts and rapid fabrication of spares in future manned missions on the Lunar surface. The structural design was validated against a set of boundary conditions (static analyses) and requirements of launch and space environments (dynamic analyses) as prescribed by European Cooperation for Space Standardization standards. The composite rover was designed to lighten the structure itself and increase the payload-to-total-mass ratio: the composite solution offers a ratio three times higher than the typical rover (ratio from 0.12 to 0.38).