A. Chrysanthou

The effect of different metallic counterface materials and different surface treatments on the wear and friction of polyamide 66 and its composite in rolling–sliding contact

Original article can be found at: http://www.sciencedirect.com/science/journal/00431648 Copyright Elsevier B. V. DOI: 10.1016/S0043-1648(03)00054-1

Fretting wear in self-piercing riveted aluminium alloy sheet

Abstract Fretting wear in aluminium alloy AA5754 joined by self-pierce riveting (SPR), a relatively new fastening technique increasingly used in vehicle structures, has been investigated in this paper. Surface damages have been induced when a joint experienced a sinusoidal cyclic tension–tension load. Various degradation zones have been characterised in the contact surfaces between the aluminium sheets, as well as the rivet and the locked sheet. Subsequent examination of the fretting scars at the contact surfaces and through the cross-section has been carried out using optical and scanning electron microscopies. The fretting patterns in the self-piercing riveted joints have been identified. It was noted that fretting wear was initially patchy and layers of compacted debris were created as fretting continued. An energy dispersive X-ray (EDX) analysis of the fretting debris from the interface between the rivet and the aluminium sheet revealed the presence of Al, Fe, Si, C and O so that it is suggested that intimate mixing of debris from the aluminium alloy and the steel rivet had occurred. The effects of testing conditions such as the load magnitude and the number of loading cycles on the fretting wear patterns were also studied. Metallographic examination has shown that these fretting zones are critical with respect to fretting crack nucleation. The test results have shown that joint fracture initiates at these critical zones.

An Evaluation of NDT for Self-pierce Riveting

An evaluation of Non-Destructive-Testing (NDT) technique based on ultrasonic inspection for selfpiercing riveted (SPR) joints was conducted. A riveted joint is inspected by an ultrasonic continuous wave through a differential piezoelectric transducer operated at a predetermined frequency. The joint quality is evaluated by monitoring variations in the electrical impedance of the transducer represented by both the phase and the amplitude displayed in the complex impedance plane. A range of SPR joints were tested using the NDT technique and the NDT results were compared with laboratory sectioning of samples. It was observed that for some of the aluminium joints with two or three layers, the NDT technique could arguably detect sound and bad joints. The work has also shown that for joints involving very thin aluminium sheets and steel panels, the sensitivity of the technique needs to be improved.

Self-Pierce Riveting: A New Way for Joining Structures

Self-pierce riveting is a relatively new joining technique that is attracting interest for various engineering applications. The process does not require a pre-drilled hole and this can eliminate the alignment problem encountered by conventional mechanical fastening. A range of materials covering similar or dissimilar materials can be joined with multiple layers by such means. The study showed that the strength and fatigue behaviour of self-piercing rivets is affected by selecting a suitable rivet and anvil design as well as suitable sheet materials. Fretting scars were observed to occur at the contact of the joined sheets near the rivet. This observation has not been reported by previous studies. It was shown that fretting leads to crack initiation and fatigue failure of the joints.© 2002 ASME

Chord line force versus displacement for thin shallow arc pre-curved bimetallic strip

A pre-curved bimetallic strip that is applied with a force in an axial orientation, i.e. along its chord line, exhibits nonlinear force–displacement characteristics. For thin bimetallic strips, whereby the radius of curvature is large compared to the thickness of the strip, the non-linearity tends to be tangent related. The new theoretical formula introduced here was correlated to the results of a set of force–displacement tests, and a good overall fit of the theory to the test data was achieved. The formula put forward in this work enables the evaluation of large chord line displacements but is limited to the permissible stress limits of the material. This work can also be directly applied to thin shallow arc beams of a single material. The application of this work is in the field of bimetallic force–displacement actuators.

The effect of setting velocity on the static and fatigue strengths of self-piercing riveted joints for automotive applications

In order to reduce vehicle weight to increase fuel efficiency and reduce C02 emission, more and more automotive manufacturers are now using lightweight materials, such as aluminium, to build part of or the whole body-in-white structure. Due to the advantages over other joining techniques, self-piercing riveting (SPR) is a main joining technique for aluminium structures. In this paper, the effect of setting velocity/force on the joint quality and performance was studied. It was found that in the range studied, the increase of setting velocity increased the static lap shear strength but reduced the static T peel strength of the SPR joints. The results also suggested that the setting velocity did not have significant influence on the lap shear fatigue strength, but the T peel fatigue strength of the joints was increasing with the increase of setting velocity until it reached certain value. An increase in the setting velocity led to a decrease in the rivet head height and an increase in the interlock. In this study, the results showed that the static lap shear strength of SPR joints increased after corrosion and the setting velocity in the range studied did not have obvious influence on the change of lap shear strength after corrosion.

Effect of Pulsed Electric Current Treatment on the Corrosion and Strength of Reinforcing Steel

The study was carried out in order to evaluate the effect of the pulsed electric current (PEC) treatment on the corrosion as well as on static strength of Polish reinforcing steel. As-received St3SX was used for investigations. Two kinds of specimens were manufactured by turning from 20 mm diameter re-bars: cylinders of 10 mm diameter and 28 mm length for corrosion tests and standard cylindrical specimens of 6 mm diameter and 30 mm length for static tension tests. Corrosion tests was performed according to the ASTM B117-97 standard. As-received steel tensile specimens and the specimens after PEC treatment were tested using a servo-hydraulic universal testing machine at the strain rate of 10-2 s-1.

A two-stage approach of manufacturing FeAl40 iron aluminides by self-propagating synthesis and pressureless sintering

ABSTRACT A two-stage sintering process was successfully used to sinter FeAl to densification levels of just above 95% at a temperature of 1300°C. In the first stage, mixed iron and aluminium powders were synthesised at 750°C via self-propagating high-temperature synthesis (SHS) to form brittle and porous Fe2Al5. Then the pellets were crushed and milled to various sizes and mixed with iron powders in the nominal composition of FeAl40 and pressurelessly sintered at a higher temperature to obtain a higher densification by taking advantage of the less violent exothermic reaction of Fe2Al5 and Fe. The intermediate and end products in SHS and sintering were characterised by SEM/EDX and XRD. The porosity level of the final FeAl40 product was controlled by the heating rate and powder size, which was also strongly influenced by the temperature, holding time and the ratio of the two powders.

Effect of pulsed magnetic treatment on the corrosion of titanium

ABSTRACT Results of corrosion tests of titanium in the initial state and after treatment using pulsed magnetic field are presented. It is shown that samples after treatment have better corrosion resistance due to the formation of denser and finer corrosion products with better adhesion to the substrate. Samples after treatment have more homogeneous microstructure due to a substantial increase of dislocations which are uniformly distributed. Mechanisms of dislocation multiplication and a model explaining the effect of the treatment on the corrosion are discussed. This paper is part of a themed issue on Materials in External Fields.

Effect of Plastic Deformation on Compliance Curve Based Crack Closure Measurement

Fatigue crack growth depends heavily on near tip stress-strain behavior controlled by many micromechanical and microstructural factors. Crack closure is widely used to rationalize crack growth behaviour under complex loading conditions. Reliable crack closure measurement is essential for enhanced damage tolerance design and remains a challenge to the industry. This paper focuses on the effect of plastic deformation ahead of a notch/crack on the non-linearity of compliance curves of 6082-T651 aluminium alloy specimens to highlight a potential issue in the conventional compliance curve based crack closure measurement technique. Experimental and numerical simulation results demonstrate that plastic deformation ahead of the notch will introduce non-linear stress-strain behavior in the absence of crack closure. It is proposed that the effect of crack tip plasticity on the non-linearity of the compliance curve be separated to obtain reliable crack closure measurement.