Utilisation of silicon rubber to characterise tool surface quality during die compaction

Abstract

A new methodology was developed to observe and measure tool wear and tool surface quality during the die compaction process. The newly developed method is a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die. After verification of the method, aluminium and iron alloy powders were compacted to quantify tool wear and tool surface quality with two die materials, tungsten carbide and tool steel. The tool surface quality was quantified by recording surface roughness of the die replicas on a surface profilometer.     

Investigation of the relationship between statistical characteristics of substrate surface roughness and the strength of adhesive joints

The relationship between statistical characteristics of butadiene styrene rubber (BSR) surface roughness and shear strength of adhesive joints has been investigated. The assumption of stationary normal distribution of coordinates of surface points was made to determine the statistical characteristics of surface roughness. The profile length above the selected level l ₁ (u) was introduced as a new surface roughness parameter to characterize adhesive penetration depth. The validity of simulated l ₁ (u) value was verified experimentally. A good correlation between experimental and calculated results was found. A relationship between adhesive penetration depth and the bonding pressure during adhesive joint preparation was also obtained. The dependences among lap shear joint strength, bonding pressure and roughness characteristic l ₁ (u) were determined.     

Fatigue characteristics of a co-cured single lap joint subjected to cyclic tensile loads

In this paper, the effect of bond parameters on the fatigue characteristics of a steel-composite co-cured single lap joint under cyclic tensile loads was experimentally investigated. We considered the surface roughness of the steel adherend and the stacking sequence of the composite adherend as bond parameters. A fatigue failure mechanism of the co-cured single lap joint was explained systematically by investigating the surfaces of failed specimens.     

A study of paint adhesion to polymeric substrates

In order to explore the fundamental mechanism of paint adhesion to polymer substrates the surface of polypropylene- ethylene propylene rubber (PP-EPR) blends was modified by flame or plasma treatments. The changes in surface composition and properties were investigated and discussed in light of the results of simple adhesion tests. The topography and surface properties of the PP-EPR samples were studied by employing various surface sensitive techniques. Additionally, the surface properties of the pre-treated PP-EPR were compared with the model polymers poly(methyl methacrylate) (PMMA) and polycarbonate (PC) displaying a poor and an excellent paint adhesion, respectively. Differential scanning calorimetry (DSC) measurements showed that the miscibility of the polymer substrate with paint components was an essential factor for the understanding of the adhesion mechanism. A general model of paint adhesion to polymer surfaces is proposed, where the degree of interdiffusion of the polymer chains of the substrate and paint in the interphase determines the adhesion strength.     

Failure analyses of cemented tungsten carbide extrusion die

Abstract

In this study, the failure of a cemented tungsten carbide extrusion die (WC–Co) which was designed for the production of 55 000 components but failed during production of third component has been investigated. The die is used for cold extrusion of auto parts components as sizing die. Sizes achieved by forging process are further refined to required fine tolerance. The component size is required to be controlled within ±20 μm. The investigations revealed that the failure is due to abusive machining of cemented tungsten carbide. Detail studies under different electrical discharge machining conditions have been made to investigate the formation of cracks and their morphology. The major cause of the failure is established as abusive electrical discharge machining conditions with higher pulse current, which lead to micro- to macrocracks at the machining stage. These cracks further enlarged under load conditions when extrusion was done. Based on this study experiments were performed under different machining conditions on the WC–Co material. Optimum parameters were established for machining and accordingly new die was designed and fabricated which is performing very well.     

Analysis of variable scale surface roughness on Si(111): a comparative Brewster angle,ellipsometry and atomic force microscopy investigation

Abstract

Brewster angle analysis (BAA) and single wavelength ellipsometry (SWE) were used to investigate the optical response of Si(111), exposed to subsequent 40% NH₄F etching steps, each persisting for 20 s. During native oxide layer etchback and anisotropic etching of the silicon substrate, ultrasmall variations were accurately observed. Contact mode atomic force microscopy (CM AFM) was performed to describe the scale dependence of roughness analysis and to correlate optical and micro-topographical information. It can be shown that BAA and SWE are of comparable sensitivity with respect to variations in film thickness and surface roughness. Quantitative analysis, however, leads to new insights into the information obtainable from the optical methods. BAA data, i.e. the Brewster angle and the reflectance at the Brewster angle, change each in a unique direction, if a clean and smooth surface slightly deteriorates. Ellipsometry, however, shows more complicated variations of the data depending on the concurrent presence of small and long correlation length surface roughness. A combination of both methods allows separating and quantification of these roughness contributions.     

A study on the lap shear strength of a co-cured single lap joint

In this paper, the lap shear strength of a co-cured single lap joint subjected to a tensile load was investigated by experimental analysis. Co-cured joint specimens with several different bonding parameters such as bond length, surface roughness, and stacking sequence of the composite laminate were fabricated and tested. The dependence of the lap shear strength of the co-cured joint on the bonding parameters was investigated from the experimental results. The failure mechanism of the co-cured single lap joint was partially cohesive failure. The lap shear strength of the co-cured single lap joint was significantly affected by the bond length and the stacking sequence of the composite laminate. However, the effect of surface roughness on the lap shear strength of the co-cured single lap joint was not so significant.     

Characterizing the mechanism of improved adhesion of modified wood plastic composite (WPC) surfaces

To have a better knowledge of the phenomena that affect the adhesion characteristics of wood plastic composites (WPCs) a series of surface treatments was performed. The treatments consisted of chemical, mechanical, energetic, physical, and a combination of energetic and physical WPC surface modifications. After each treatment, the composite boards were bonded using a commercial epoxy adhesive, and bond shear strength was determined according to ASTM D 905. All the surface treatments, except the mechanical one, were performed and presented in a previous paper (W. Gramlich et al., J. Adhesion Sci. Technol. 20, 1873–1887 (2006)). Mechanical treatment and surface characterization for all the treatments were performed in the present study. The surface characterization included application of thermodynamic and spectroscopic techniques. Most of the surface treatments improved the adhesive bondability of wood plastic composites and, particularly, the smoothest WPC surfaces increased the shear strength by 100% with respect to the control. Thermodynamic measurements indicate that the WPCs low surface energy of about 25 mJ/m², is likely due principally to the surface migration of a lubricant component used in the extrusion formulation. The surface energy increased over 45% with respect to the control samples after the chemical treatments. X-ray photoelectron spectroscopy analysis indicated that high oxidation levels of the WPC surfaces resulted in high surface energy and high bond shear strength.     

Tensile load-bearing capacity of co-cured double lap joints

The co-cured joining method has several advantages over the adhesively bonded joining method because both the curing and the joining processes for the composite structures are achieved simultaneously. In this study, the tensile load-bearing capacities of co-cured double lap joints were investigated experimentally and compared with the analytical results calculated by finite element analysis. Co-cured double lap joint specimens with several bond parameters such as bond length, surface roughness, and stacking sequence of the composite laminate were fabricated and tested. From the experimental results, it was found that the failure mechanism of the co-cured double lap joint was cohesive failure by delamination at the first ply of the composite laminate in the co-cured double lap joint. Finally, optimum values of several bond parameters were determined. Analytical tensile load-bearing capacities of the co-cured double lap joints were calculated by the three-dimensional Tsai-Wu failure criterion using stress distributions obtained from finite element analysis.