Effect of Co60 gamma ray irradiation for carbon fibre on interfacial properties in epoxy resin composites

Abstract

In order to improve the interfacial adhesion between carbon fibre and resin matrix in composite materials, it is necessary to treat the surface of the carbon fibre. In this paper, γ-ray irradiation technique was used to modify polyacrylonitrile based carbon fibre. Laser Raman spectrum and X-ray photoelectron spectroscopy were used to investigate and analyse the structure and chemical composition near the surface of the carbon fibre. The influence of irradiation parameters on the interlaminar shear strength (ILSS) of carbon fibre reinforced epoxy composite materials and the bundle tension strength of carbon fibre was studied. The interfacial adhesion behaviour of composites was characterised using torsional braid analysis. The results show that after irradiation the ILSS of the composite was increased by 20%, while the glass transition peak of the specimen, determined from torsional braid analysis, shifts towards a higher temperature compared with an unirradiated specimen. The value of the glass transition temperature T _g is increased from 416.8 to 424.3 K. After irradiation there was no apparent change in the bundle tensile strength of carbon fibre. Investigations indicate that after irradiation the decrease of microcrystal size, the increase of surface free energy of carbon fibre surface and the active chemical function group formed from unsaturated carbon atoms improve the interface adhesion between the carbon fibre and the matrix in the composites.     

Microstructure and abrasive wear behaviour of iron base hardfacing

Abstract

The influence of the composition and heat treatment of overlays on the abrasive wear resistance of iron base hardfacing alloy overlays is reported. Overlays were deposited using a shielded metal arc (SMA) welding process on structural steel using two commercial hardfacing electrodes, i.e.Fe – 6%Cr – 0.7%C (H₁) and Fe – 32%Cr – 4.5%C (H₂). Abrasive wear resistance of overlays in as welded and heat treated conditions was tested using a pin on disc system against a 300 grade waterproof SiC polishing paper at different normal loads (1 – 4 N) and constant sliding speed 2.0 m s^-1. Optical microscopy was used to study the microstructure of overlays in as welded and heat treated conditions. SEM studies of wear surfaces were carried out to analyse wear mechanisms. It was found that the wear resistance of the high Cr – C coating is better than the low Cr – C hardfacing under identical conditions. Significant variation in hardness was noticed across the interface, indicating the effect of dilution. Hardness of the coating adjacent to the interface was found to be comparatively lower than the coating further away from the interface. Post-weld heat treatment enhanced the abrasive wear resistance.     

Overload failure behaviour of dissimilar thickness resistance spot welds during tensile shear test

Abstract

Resistance spot welding is the dominant process for joining sheet metals in automotive industry. Even thickness combinations are rarely used in practice; therefore, there is clearly a practical need for failure behaviour investigation of uneven thickness resistance spot welds. The aim of the present paper is to investigate the failure mode and failure mechanism of dissimilar thickness low carbon steel resistance spot welds during tensile shear overload test. Microstructural investigations, microhardness tests and tensile shear tests were conducted. Mechanical properties of the joints were described in terms of peak load, energy absorption and failure mode. In order to understand the failure mechanism, micrographs of the cross-sections of the spot welded joints during and after tensile shear are examined by optical microscopy. It was found that for well established weld nuggets, the final solidification line is located in the geometrical centre of the joint. In pull-out failure mode, failure is initiated by necking of the base metal at the thinner thickness sheet. Finally, it was concluded that weld nugget size, weld penetration and the strength of the thinner sheet are the main controlling factors of the peak load and energy absorption of dissimilar thickness spot welds.     

Laser surface alloying of 1045 AISI steel using Ni–CrB2 powder

Abstract

Laser surface alloying is a process whose purpose is to improve the surface properties by incorporating alloying elements into the surface. The advantages of using laser for surface treatment are: formation of a non-equilibrium or amorphous phase as well as homogenisation and refinement of the microstructure, all without affecting the substrate properties. Powder (50 wt-%Ni–50 wt-%CrB₂) was injected into a melt pool created by a CW–CO₂ laser on AISI1045 steel plates. In order to alloy the entire surface, the sample was scanned at scan speeds in the range of 600–6000 mm min^–1 and the laser power was in the range of 1750–2500 W. The powder feed rate was 1·6 g min^–1, the laser beam was 2 mm in diameter, with 60% overlap between successive laser paths. Metallographic cross-sections were made of the samples. For each sample the following properties were characterised: layer depth, microhardness (HV), layer microstructure and composition. It has been found that the scan speed and the laser power affect the depth of the melt pool, the microstructure, the hardness and the treated layer composition. The laser boronised surface exhibits better wear resistance than D2 tool steel hardened to 59 ± 1 HRC. This will be discussed based on numerical analysis of the laser/material interaction.     

Microstructural evolution an dmechanical properties of Rapidsteel 2.0

Abstract

At present, the research on rapid tooling by the selective laser sintering (SLS) method is mainly focused on the production of parts with high accuracy and definition. Very little effort has been devoted to the microstructural evolution and mechanical properties of this material. This paper gives detailed information about microstructural development and mechanical behaviour of Rapidsteel material after subsequent heat treatment cycles for binder removal, partial sintering, and liquid phase infiltration.

The microstructure of SLS samples heated to 1120°C for 3 h in 30H₂-70N₂ atmosphere at 2 K min^-1 consisted of a mixture of austenite, M₂₃C₆, and Cr₂N phases. Subsequent infiltration of the above sample with bronze at 1050°C for 2 h in 30H₂-70N₂ atmosphere at 2 K min^-1 produced similar phases together with an additional α(Cu-Sn) phase. The mechanical tensile fracture strength of the partially sintered part increased ten times after infiltration with bronze. However, the fracture behaviour is found to be different between the samples subjected to various heat treatment cycles. The sample heated after the first cycle showed fracture along the necks between stainless steel particles, whereas the infiltrated sample showed fracture along the bronze infiltrant.     

Effect of MnS powder additions and vibratory ball peening on corrosion resistance of sintered 316LSC stainless steels

Abstract

As sintered parts are to be machined after sintering, the MnS powder is usually added to improve the machinability. Vibratory ball peening is used for deburring and improving the surface finish of sintered components in local PM industries. The effect of the MnS powder content and vibratory ball peening on the corrosion resistance of the sintered 316LSC alloys was investigated. Experimental results show that the addition of MnS powder slightly decreases the sintered density. The weight loss rate of the sintered specimens immersed in the 10%FeCl₃ corrosion test solution increases slightly with increas- ing MnS content, but decreases with increasing sintering temperature. Vibratory ball peening effec- tively decreases the weight loss rate of the sintered stainless steels. The chromium atoms actively migrate across the phase boundary and diffuse into the MnS particles during sintering. This intensive chromium diffusion affects the corrosion performance of the sintered alloys with MnS added. The surface morphology of the as sintered and the ball peened specimens before and after the corrosion test were studied with a SEM.     

Design criteria for rolling contact fatigue resistance in back-up rolls

Abstract

This research centres on surface initiated damage on back-up rolls whereby rolling contact fatigue cracks can propagate into the rolls potentially reaching the internal stress fields and leading to catastrophic failure and has sought to establish design criteria for avoiding such failures. The project objectives have been achieved by examining field evidence, determining the loading and tribological conditions at the work roll/back-up roll interface and investigating both theoretically and experimentally the mechanisms involved in rolling contact fatigue in this case. The presented rolling contact, fatigue and fracture mechanics model includes criteria for crack branching either upwards (i.e.relative safety) or downwards (i.e.potentially catastrophic) and the link between these two cases is related, quantitatively, to the properties of the roll material. After linking mechanics to microstructure, the influence of work roll test disc surface roughness on both the surface wear of and the interaction between wear and rolling contact fatigue at the surface of back-up roll test discs has been quantified using the results obtained from experimental simulations carried out on a rolling–sliding testing machine. Finally practical quantitative recommendations are made for the mechanical and microstructural design of bainitic back-up roll materials, back-up roll redressing procedures and the surface roughness of both work rolls and back-up rolls presented to the mill.     

Flux shielded arc butt welding of concrete reinforcing steel

Abstract

The present paper reports on a new variant of flux shielded arc butt welding without the addition of a filler material, applied to steel bars for concrete reinforcement. The welding process is described, including the arc ignition and forcing together of the workpieces, via the application of a mechanical force, to form an upset. A new portable machine is described, using which it is possible to apply flux shielded arc welding on site. Experiments were carried out, from which optimum welding parameters such as welding current, weld time, and upsetting force were found. The strength properties of the welded joints obtained were determined via mechanical testing, i.e. a bend test, a tensile strength test, and an impact toughness test. Macroscopic sections of the welded joints were also produced. A quality analysis of the butt welded joints showed that the mechanical properties of the joints were equivalent or even superior to the properties of the parent metal.     

Fracture toughness of structural aluminium alloy thick plate joints by friction stir welding

Abstract

The fracture toughness in a friction stir welded joint of thick plates of structural aluminium alloy type A5083-O is investigated. A joint between two 25 mm thick plates is fabricated by one sided, one pass friction stir welding. The Charpy impact energy and critical crack tip opening displacement (CTOD) in the friction stir weld are much higher than those in the base metal or heat affected zone, whereas mechanical properties such as stress–strain curve and Vickers hardness are not conspicuously different. The effects of the microstructure on crack initiation and propagation are studied in order to clarify the difference in fracture toughness between the stir zone and base metal. The analyses of the fracture resistance curves and the diameters of dimples in the fracture surface after both tensile and bending tests show that the fine grained microstructure in the stir zone helps to increase ductile crack initiation and propagation resistance. It is found that the high fracture toughness value in the stir zone is affected by the fine grained microstructure in friction stir welds.     

Development of high quality thermal spraying process by shielding control

Abstract

The shielding controlled plasma spraying process was investigated to improve corrosion resistance of metal surfaces. In this process, a shielding nozzle that covered only spraying area was attached in front of the tip of a commercial plasma spray gun nozzle, and the environment surrounding the plasma jet was controlled by nitrogen flow. When the oxygen concentration in the shielding nozzle was maintained at 0·5%, the metal oxide contents in CoNiCrAlY coating and the porosity of the coating reduced to 0·2 and 0·3% at optimal spray particle size respectively. The corrosion potential in an acid solution including chloride ions was almost constant for 1000 h for CoNiCrAlY coating deposited by shielding controlled plasma spraying. On the other hand, those obtained by atmospheric plasma spraying process decreased in the corrosion potential largely after 10 h. Thus, it can be concluded that the shielding controlled plasma spraying process improves the corrosion resistance of the metal.