Laser-deposit welding, by using Nd-YAG, is a mould repairing process, which has the advantages relatively to the traditional methods of achieving a less change of the metal composition around the repaired zone and permitting a very accurate deposition of a small volume of the filler material in the area chosen at the work-piece surface. This paper presents a fatigue study in specimens of two base materials used in mould production (AISI H13 and P20). Filler material as well as welding parameters were analysed in order to obtain better fatigue strength. The tests were carried out under constant amplitude loading, with two stress ratios R = 0 and R = 0.4. Welded specimens were prepared with V notches and filled with laser welding deposits. The fatigue results are presented in the form of S-N curves obtained in welded and non-welded conditions. Complementary measurements of hardness profiles and SEM analysis were carried out to understanding the fatigue behaviour and failure sites. The laser-deposit material was the weaker region in both steels, due to a high level of tensile residual stresses and also to some planar defects that are potential failure sites. Fatigue crack initiation is therefore reduced and the fatigue propagation life is enhanced. A significant mean stress effect in the base material was also observed in both mould steels.

Aluminized glass fiber composites in a polyester matrix were used in this work in an attempt to study their fatigue resistance under both dry and water saturated ambient conditions (compared to conventional glass fiber composites). These composites, containing specially modified fibers, exhibit increased thermal and electrical conduction properties whilst still being potentially adequate for many structural applications. The fatigue tests were performed in tension at ambient temperature and a frequency of 10 Hz. The fatigue damage of aluminized composites are described and evaluated in under environmental conditions and compared to the performance of uncoated fiber composites.

This paper presents a fatigue study in Nd-YAG laser surface repairing welded joints in specimens of two base materials used in mould production. The tests were carried out in a servo-hydraulic machine in tension, under constant amplitude loading, with two stress ratios R = 0 and R = 0.4. Welded specimens were prepared with U notches and filled with laser welding deposits. The fatigue results are presented in the form of S-N curves obtained in welded and non-welded conditions. Complementary measurements of hardness and residual stresses profiles were carried out along the surface of laser welded specimens to understand the observed fatigue behaviour. The melted material was the weaker region, with lower values of hardness and higher tensile residual stresses, presenting also a high number of defects that are potential failure sites. The presence of such defects can explain the relatively poor fatigue strength of the laser repairing joints in comparison to base materials.

a b s t r a c tLaser deposit welding based on modern ND-YAG lasers is a new mould repair process with advantages relatively to the traditional methods (micro-plasma and TIG methods), namely deposition of small volumes of the filler material without distortion. Residual stresses play a major role on the fatigue and thermal-mechanical fatigue behaviour of welds. This paper presents the experimental results and numerical predictions of the residual stresses in joints manufactured with two hot-working tool steels: X.40.CrMoV.5.1 and 40.CrMnNiMo.8.6.4, in the laser-deposited layer and in the heat-affected zone. Welded specimens were prepared with U notches and filled with ND-YAG laser welding deposits. Trough-depth residual stresses evaluation after laser deposit welding were performed in order to analyse the influence of the residual stress state on fatigue behaviour of mould steels. Both X-ray diffraction sin 2 c method (XRD) and incremental hole-drilling technique (IHD) were used in residual stress measurement. Numerical predictions of the residual stress distributions were obtained for several values of the technologic parameters, compared with experimental results and discussed based on the assumptions stated.

Aluminized glass fiber composite with epoxy and polyester matrix were used in this work in order to study fatigue properties and its comparison to conventional glass fiber composites. Until now aluminized glass fiber materials have been only used as decoy flares in military applications. The innovative advantages of these composites, using modified fibers, are potentially the improvement of thermal and electrical conduction. The main objective of this work was to study the fatigue damage of coated fiber materials using stiffness loss and potential drop techniques. The failure mechanisms were analyzed using microscopy. Fiber contents and the resin effects in the fatigue strength were also tested and discussed.