The effects of porosity on the matrix-dominated mechanical properties of unidirectional carbon fiber-reinforced plastic composites were evaluated using X-ray computed tomography and mechanical testing. Carbon fiber-reinforced plastic plates of four porosity levels were manufactured by implementing different curing cycles. Porosity was detected by X-ray computed tomography tests, conducted on samples taken from the plates, and quantified by analyzing the computed tomography scans using the VGStudio Max software. Four different types of mechanical tests were conducted; namely, transverse tension, V-notched rail shear, three-point bending, and short-beam shear tests. The porosity analysis showed that with increasing the porosity volume fraction, the number of pores decreases, their volume increases while their shape changes from spherical or ellipsoidal to a needle-shape. The results from mechanical tests reveal that the presence of pores reduces all matrix-dominated material properties of the UniDirectional (UD) carbon fiber-reinforced plastic material. The reduction in strength is greater than the reduction in the elastic properties. Moreover, the reduction in the in-plane shear and interlaminar properties is greater than the tensile properties of the UD carbon fiber-reinforced plastic material. Between porosity contents of similar volume fraction, the one with the few large pores proved more severe than the one with the many small pores. The large standard deviation observed for some of the tests is attributed to the non-uniform dispersion of pores.

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<p class="Abstract"><span lang="EN-US">In this work, the additive manufacturing process selective laser melting is analysed with the aim of realising a complex piece for aerospace applications. In particular, the effect of the manufacturing process and of the following thermal treatments on the dimensions of the workpiece is evaluated. The study is based on a hybrid approach including a simulation of the whole manufacturing process by advanced software packages and the dimensional measurements of the realised pieces taken by a coordinate measuring machine (CMM). The integrated use of simulation and measurements is carried out with the aim of validating the simulation results and of identifying the operational limits of both approaches; this analysis is based on metrological evaluation of the results of both the simulation and the tests, taking into account the uncertainty of the data. In addition, the main causes of uncertainty for the simulation activity and the experimental data have been identified, and the effects of some of them have also been experimentally evaluated. Based on the experimental validation, the simulation seems to predict the absolute displacement of the supports of the piece in a satisfactory way, while it is unable, in the actual configuration, to assess the conformity of the surface to its very tight shape tolerances. Conformity assessment of the surface should be carried out by CMM measurement. Integrated use of simulation and experimental results is expected to strongly improve the accuracy of simulation results for the effective and accurate design and control of the additive manufacturing process, including dimensional control and thermal treatments to mitigate induced thermal stresses.</span></p>

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