J.D. Costa

Analysis of fatigue and damage in glass-fibre-reinforced polypropylene composite materials

Abstract This paper concerns fatigue studies of polypropylene/glass-fibre thermoplastic composites produced from a bi-directional woven cloth of co-mingled E-glass fibres and polypropylene fibres with a fibre volume fraction V f of 0.338. The effect of lay-up design and load conditions on fatigue performance were investigated. The S-N curves, the rise in the temperature of the specimens, and the loss of stiffness during the tests, are discussed. Fatigue tests were performed in controlled displacement mode and in an imposed stress range. Similar results were obtained for both load conditions. The loss of stiffness was used as a damage parameter and related to the rise of temperature. The results show that the damage parameter E present a nearly linear relationship with the rise in temperature. A small deviation was probably caused by the stress release observed in the first period of fatigue life. ©

Effect of notch and test conditions on the fatigue of a glass-fibre-reinforced polypropylene composite

This paper is concerned with fatigue studies of polypropylene/glass-fibre thermoplastic composites produced from a bidirectional woven cloth of commingled E-glass and polypropylene fibres (the latter becoming the matrix after the application of heat and pressure). This composite was manufactured with a fibre volume fraction of 0.338. The effects of frequency, stress ratio, temperature and stress concentration on the fatigue performance were considered. The stress concentration was induced by circular holes in specimens loaded in tension. Stress/life fatigue curves, the rise in temperature of the specimens during the tests and the loss of stiffness were obtained and are discussed.

Static and fatigue behaviour of glass-fibre-reinforced polypropylene composites

Abstract This paper is concerned with fatigue of polypropylene/glass-fibre thermoplastic composites produced from a bi-directional woven cloth mixture of E glass fibres and polypropylene fibres. The latter becomes the matrix after the application of heat and pressure. This composite was manufactured with a fibre volume fraction Vf of 0.338. The effect of layer design on the static and fatigue performance was investigated. The S–N curves, the rise in the temperature of the specimens during the tests and the loss of stiffness, were obtained and discussed. The loss of stiffness was related to the rise of temperature and stress release observed in the material. The effect of load rate on the static properties was also studied and discussed accordingly.

Fatigue life prediction in AlMgSi1 lap joint weldments

The fatigue behaviour of an AlMgSi1 alloy lap welded joint and the improvement in fatigue strength due to post-weld heat treatment were investigated. Two series of fatigue tests were performed: one in as-welded specimens and another in heat-treated specimens. The prediction of crack initiation life under a plane strain condition was made based on the local strain approach using Morrows modified equation. The local inelastic stresses and strains at the weld toe were calculated for the heat-treated specimens using three methods: Neuber, Glinka and finite element analysis. The accuracy of the different methods were evaluated and discussed.

Fatigue and fretting fatigue of ion-nitrided 34CrNiMo6 steel

Abstract This work is concerned with the surface treatment (ion nitriding) of fretting fatigue and fatigue resistance of 34CrNiMo6. Tests are made on a servo-hydraulic machine under tension for both treated and non-treated specimens. The test parameters involve the applied displacements δ ±80–±170 μm; fretting pressure σ n =1000–1400 MPa; fatigue stress amplitude σ a =380–680 MPa and stress ratio R =−1. The ion nitriding process improves both fatigue and fretting fatigue lives. Subsurface crack initiation from internal discontinuities was found for ion-nitrided specimens.

Fracture assessment of PMMA/Si kitchen sinks made from acrylic casting dispersion

Abstract Acrylic casting dispersion is used to fabricate kitchen sinks made of PMMA/Si which stands for poly-methyl methacrylate mixed with a fine dispersion of silica. The composite is suited for sanitary wares that are subjected to severe temperatures, giving rise to high thermal stresses. This leads to failure by cracking in the region near the drain hole. Such conditions are investigated by determining the mechanical and fracture properties for two different chemical compositions of PMMA. They are referred to by trade marks from ICI as Asterite and Amatis. Data are obtained for temperatures from 0 to 95 °. Extensometry data are also obtained to the thermal stresses around the drain hole subjected to alternating flow of cold and hot water. Critical crack lengths are determined from the critical stress intensity factor and maximum local tensile stresses based on measured data. They are estimated to be 1.5 mm and 4.0 mm, respectively, for the Asterite and Amatis composites. These results confirm with practice where the cracking of the former was observed while the latter did not crack.

Fatigue behaviour of 42Cr Mo4 steel with PVD coatings

This paper presents results concerning the fatigue strength for 42Cr Mo4 steel coated by physical vapour deposition (PVD). The raw material is compared with the material coated with W, WN, WTi and WTiN coatings. Fatigue tests were performed by three point bending under repeated loading cycle at room temperature using a sinusoidal wave loading with frequency of 25 Hz. From the experimental results, it can be concluded that the fatigue lifetime of specimens coated by PVD compared with uncoated specimens only increases for the region of low stress amplitudes and for the WTi film coating. For high stress amplitudes and for other coatings the life of coated specimens did not increase when compared with the uncoated specimens. In general crack initiation in the substrate near flaws in the coating film was observed.

Fatigue life predictions in polymer particle composites

Abstract This paper presents a study on fatigue life predictions in three polymer particle composites with different volume fractions of filler and different particle sizes. Central hole notched specimens were analysed using a fracture mechanics approach. A solution for the stress intensity factor of corner cracks at a hole was obtained using the finite element method and considering quarter-circular and quarter-elliptical cracks of different sizes. The solution was compared with a literature solution and significant differences were found. Fatigue crack propagation tests were performed at room temperature and constant loading amplitude, for stress ratios R=0 and R=−0.75. Finally, fatigue lives, crack shape evolution and final crack length were predicted assuming an initial crack size and considering that the crack maintains a quarter-elliptical shape. The comparison with experimental fatigue lives indicated the presence of initial defects larger than the silica particles; however, these large sizes can be explained by the residual stresses measured near the hole.

Morphology of Copper Coatings Electroplated in an Ultrasonic Field

This paper reports the study of ultrasonic effects on some physicochemical properties of electroplated copper on iron subtracts from an acid sulphate bath. The bath efficiency for three stirring processes has been also studied as a function of the time and the current density applied. The bath efficiency, the hardness, the brightness and the adherence of the electrodeposits increase with the ultrasonic agitation, in comparison with the same coatings produced from still or magnetic stirred baths. Scanning electron microscopy (SEM) analysis has revealed a compact and more order structure in the coatings performed under ultrasonic waves at high current densities, conversely to free and dusty obtained with still bath.

Influence of spectrum loading on fatigue resistance of AA6082 friction stir welds

Purpose – Welded components are often subjected to variable amplitude service loads, increasing the uncertainty of fatigue life due to material strength, notch geometries, defect content and residual stresses. In the case of friction stir welding (FSW) of aluminium alloys no data were found available concerning fatigue behaviour under variable amplitude loading. The purpose of this paper is to determine the fatigue strength of friction stir welds in AA6082‐T6 under constant and variable amplitude loading and analyse the validity of Miners rule for these specific welding conditions.Design/methodology/approach – Fatigue tests were carried out in a servo‐hydraulic testing machine using a stress ratio of R=0. Typified Gassner amplitude spectra were considered, using four shape exponent values. Microhardness tests were performed to characterize the Vickers hardness profile in the vicinity of the weld area. Relatively to the base material (BM), the FSW process leads to a decrease of the static mechanical prope...