A new damage index to monitor the range of the penetration process in thick laminates

Abstract

A damage variable (damage degree DD) representing the ratio between the absorbed energy and the impact energy was introduced in 1998 by Belingardi and Vadori to assess damage accumulation caused by low-velocity impacts. More recently, repeated impact tests carried out on thick laminates pointed out the significance and extent of the penetration process in thick laminates, which the DD is unable to monitor as, by definition, it reaches the value of one at penetration to remain unchanged over the entire penetration process. In the present paper, a new damage variable (damage index DI) is proposed to overcome shortcomings of the DD with respect to thick laminates. By introducing the displacement of the impactor into the definition of the DI, the depth of the penetration process is taken into account. Normalization by the displacement of the quasi-static perforation test allows for a non-dimensional damage variable which is shown to reach the value of one at perforation. Validity of the approach is proven against impact data obtained for different fibre-matrix architectures and laminate thickness. Results show that the DI can effectively differentiate between penetration and perforation thresholds, increasing monotonically within the range of the penetration process. In particular, the DI is shown to increase linearly with the impact energy up to penetration and to rise quite abruptly within the range of the penetration process. Results for repeated impact tests prove that at first the DI increases quite linearly impact after impact, owing to a steady accumulation of damage. A few impacts before penetration a sudden rise in the DI value points out a change in the rate of damage accumulation.

Repeated impact response of hand lay-up and vacuum infusion thick glass reinforced laminates

“…2) and equals the friction force of the dart sliding through the penetrated specimen. For all the laminates tested in [7] the s MAX measured in perforation tests was practically equal to s QS , so that the DI reaches the value of one at laminate perforation.…”

“…Four falling heights are considered, corresponding to conditions of no perforation within test duration and to conditions of laminate perforation. The impact response is evaluated in terms of damage progression by visual observation of the impacted specimens, evolution of the peak force (maximum of the load-displacement curve) and of stiffness loss as a function of impact number, and by calculating the damage index (DI), a damage variable recently proposed by the authors [7] to monitor the penetration process in thick laminates.…”

Assessment of Residual Elastic Properties of a Damaged Composite Plate with Combined Damage Index and Finite Element Methods

“…In this paper, the detecting Damage Index (DI d ) technique was adopted for assessing the local residual elastic properties of a composite laminate. This methodology was brought in the realm of the non-destructive characterization for components made of composite material by Belingardi et al in [11][12][13][14][15]. The DI d technique consists of two sets of experimental tests: a preliminary characterization activity which is performed to identify the correlation between residual elastic properties of the material and the DI d parameter and the proper non-destructive test to estimate the local residual elastic properties of the investigated component from the DI d .…”

Dynamic response of composite laminated beams under asynchronous/repeated low-velocity impacts of multiple masses

“…Belingardi et al [31][32][33] have introduced a new damage index to assess damage accumulation for repeated impacts on thick laminated plates and used it to compare the two manufacturing techniques (vacuum infusion and hand lay-up) and measure the rate of growth of steady damage accumulation in separate researches.…”