Variable Block Loading Research Articles

Fatigue Performance of Hybrid Steel Samples with Laser Sintered Implants

Laser sintering metal has recently been used in the manufacture of metallic structural hybrid components comprising two different materials obtained by two distinct technological processes. This process allows to obtain productivity gains reducing sintering time and hence the cost. In current study it was used a machined substrate in which it is built by sintering the remaining part. The purpose of present work was to study the effect of the substrate material and interface microstructure on the fatigue performance under constant and variable block loadings. The sintering laser parts were manufactured in maraging steel AISI 18Ni300, while the substrates of hybrid specimens were produced alternatively in two materials: the steel for hot work tools AISI H13 and the stainless steel AISI 420. Fatigue strength will be quantified in terms of S - N curves. The results show that tensile properties of sintered specimens and of the hybrid parts was similar. Fatigue strength for short lives, of the sintered specimens and hybrid parts was quite similar. However, the fatigue strength of hybrid parts tends to decrease, for long lives, when compared with single sintered specimens. The fatigue tests under block loadings leads to indicate that the application of Miner's law is adequate to predate fatigue life in hybrid components with sintered implants, despite having been observed a tendency to be conservative for long life.

Fatigue life evaluation for carbon/epoxy laminate composites under constant and variable block loading

This paper presents the results of current research on the fatigue life prediction of carbon/epoxy laminate composites involving twelve balanced woven bidirectional layers of carbon fibres and epoxy resin manufactured by a vacuum moulding method. The plates were produced with 3 mm thickness and 0.66 fibre weight fraction. The dog bone shape specimens were cut from these plates with the load line aligned with one of the fibre directions. The fatigue tests were performed using load control with a frequency of 10 Hz and at room temperature. The fatigue behaviour was studied for different stress ratios and for variable amplitude block loadings. The damage process was monitored in terms of the stiffness loss. The fatigue life of specimens submitted to block loading tests was modelled using Palmgren–Miner’s law and taking in to account the stress ratio effect. The estimated and experimental fatigue lives were compared and good agreement was observed.