Issue 19

G. Bolzon et alii, Frattura ed Integrità Strutturale, 19 (2012) 20-28; DOI: 10.3221/IGF-ESIS.19.02 21 order to characterize the mechanical properties and to follow the evolution of the damaging phenomena leading to failure of the composite and of its constituents. A brief overview of current research activities in this field is presented in [1]. This communication focuses on the procedures implemented for the determination of the fracture properties of the thin aluminium inclusions embedded in the anisotropic paperboard composites in the cap opening areas. The sought mechanical characteristics are deduced from the results of tensile tests performed on strips of the heterogeneous material under consideration. The main information about the deformation and the damaging phenomena developing in the specimens is collected by the continuous monitoring of the region of interest by a digital camera. Snapshots are processed by Digital Image Correlation (DIC) techniques, introduced in [2], to recover quantitative data. DIC techniques permit to reconstruct the whole deformation history of the specimen in the field of view of the camera with high accuracy in contact−less mode. These interesting characteristics foster the continuous development of the methodology with the reduction of the elaboration time, the optimization of the computer algorithms and the improvement of the measurement precision. Consequently, the application field of this technique is progressively enlarged and recent contributions include metals [3], wood [4], transparent media [5] and plastics [6, 7] among others. In this investigation, the interpretation of the large amount of experimental data recovered by DIC is supported by the numerical simulation of the tests. Fracture properties are then inferred though inverse analysis tools, as illustrated in next Sections. E XPERIMENTAL PROCEDURES he mechanical response of paper–based materials is usually recovered from tensile tests, performed according to Standards [8] on strips of dimensions 15×180 mm 2 cut from the material batches to be investigated. This experimental setup has been exploited also for the characterization of the aluminium laminate inclusion shown in Fig. 1(a) in a configuration close to ultimate failure. The material under investigation consists of a thin aluminium foil (a few μm thick) coated by polymeric layers and embedded in the paperboard composite. The main mechanical degradation phenomenon of this material system consists of the separation of the aluminium foil in the laminate inclusion at the interface with the paperboard composite. The standard tensile test is carried out under displacement control. The equipment returns the load-displacement curve shown in Fig. 2, which reflects the overall behaviour of the heterogeneous specimen all along the experiment. In particular, the long plateau on the tail of the curve represents the residual load carrying capacity of the specimen due to the presence of the polymeric layers, which undergo large deformations after their separation from the stiffer aluminium foil. Figure 1: Failure of a heterogeneous specimen under tensile test (a) and the finite element simulation of the experiment (b) . T (a) (b)