Pasqualino Corigliano

Experimental and numerical analysis of fillet-welded joints under low-cycle fatigue loading by means of full-field techniques

The welded structures used in the naval field are generally subjected to fluctuating stress over time. In some structural welded details, due to changing loading conditions, significant elastic-plastic deformation can arise, which may lead to the failure of the structure after a relatively low number of cycles. The aim of this scientific work was to investigate the behavior of welded T-joints under low-cycle fatigue using full-field techniques: digital image correlation and infrared thermography. Low-cycle fatigue tests were carried out on welded “small-scale” specimens with the aim of obtaining loading and boundary conditions similar to those that occur in “large-scale” components in their real operating conditions. A nonlinear finite element analysis was also performed. The material curves, relative to different zones (base material, heat-affected zone, weld), were obtained by hardness measurements, which were done by means of a fully automated hardness scanner with high resolution. This innovative technique, based on the ultrasonic contact impedance method, allowed to identify the different zones (base material, heat-affected zone, weld metal) and to assess their cyclic curves, which were considered in the finite element model. Finally, the finite element model was validated experimentally comparing the results with the measurements obtained using the digital image correlation technique. The applied procedure allows providing useful information to the development of models for the prediction of fracture and fatigue behavior of the welded joints under the low-cycle fatigue loading.

Experimental investigation on Iroko wood used in shipbuilding

The paper deals with investigations about mechanical properties of Iroko, a hardwood species used for structures in shipbuilding as glued laminated timber. Experimental tests have been carried out to assess strength, stiffness and density of Iroko in accordance with current EN Standards. All the results obtained by tensile and three-point bending tests, along with the statistical analyses performed to define the characteristics values of some mechanical properties, are reported in the paper. These values allowed to assign the strength class, reported in EN 338 Standard, to the investigated Iroko wood population. The experiments have taken into account both solid timber strips and scarf-jointed strips, in order to evaluate the influence of such a type of joint, which is widely used in wooden shipbuilding on strength and stiffness. Eventually, peculiar investigations have been carried out to analyse the failure mode of some test pieces through special experimental techniques: three-dimensional computed tomography and infrared thermography.

Fatigue assessment of Ti-6Al-4V titanium alloy laser welded joints in absence of filler material by means of full-field techniques

The aim of this research activity was to study the fatigue behavior of laser welded joints of titanium alloy, in which the welding was performed using a laser source and in the absence of filler material, by means of unconventional full field techniques: Digital Image Correlation (DIC), and Infrared Thermography (IRT). The DIC technique allowed evaluating the strain gradients around the welded zone. The IRT technique allowed analyzing the thermal evolution of the welded surface during all the fatigue tests. The fatigue limit estimated using the Thermographic Method corresponds with good approximation to the value obtained from the experimental fatigue tests. The obtained results provided useful information for the development of methods and models to predict the fatigue behavior of welded T-joints in titanium alloy.