Non-destructive evaluation of residual elastic properties in composite components after impact

The detection and evaluation of damage in components made by composite materials is one of the main concerns for automotive engineers. It is acknowledged that the damage of this type of components can be originated both by impact and fatigue loading. The paper is devoted to the damage due to impact loading. Long fiber-reinforced plastic represents, at the moment, one of the most interesting composite materials for automotive components in the lightening perspective that brings along reduction of fuel consumption and of Green House Gas emissions. Based on our long-lasting experience on the impact behavior of composite materials, that includes repeated impact loading conditions, we proposed an innovative simplified non-destructive methodology for the assessment of the damage sustained by composite materials. The methodology was specifically devoted to the detection and evaluation of the relevance of the sustained damage. This evaluation is made in terms of residual elastic properties and, consequently, of residual strength. The proposed methodology was applied and validated on plate specimens. A good correlation was found between the predicted and the actual residual elastic properties of the damaged composite plate. Subsequently, the methodology was applied to a composite beam, with an omega shape transverse section, that represents one of the typical beams used in the frame of a car body. With the proposed methodology, it could be possible to choose the proper maintenance activity after a damaging event: a - do not repair, since damage is not affecting the structure performance; b - repair, since damage is lightly affecting the structure performance; c - substitute, since damage is relevant and the component is no longer able to carry the characteristic service loads.