John C. Betts

A Progressive Failure Analysis Applied to Fiber-Reinforced Composite Plates Subject to Out-of-Plane Bending

The ability to predict the structural response of composites offers a significant advantage to design engineers and provides the possibility of identifying structurally efficient composite assemblies. Various analytical and numerical models are possible, but care has to be taken to ensure that the appropriate structural performance and failure criteria are used. In particular, modeling the progressive failure of composite laminas requires robust and validated failure algorithms that are not only computationally efficient, but are also able to predict the load–deformation characteristics and to ultimately establish the failure load appropriately. This study looks into different progressive failure macromechanical algorithms applied to e-glass-fiber-reinforced composite plates subject to out-of-plane bending. The influence of different boundary conditions of the plates, ranging from fully clamped to simply supported ones, on their ultimate failure load is also investigated. The results are validated by experimental data found in the literature and show that boundary conditions have a significant influence on the predicted ultimate failure load. The study also shows that, in this case, the predominant failure mechanism is the failure of matrix, and after the redistribution of stresses, no consecutive failure due to fiber or fiber-matrix failure occurs in the lamina, therefore a sudden-degradation progressive ply failure algorithm based on the failure mode is sufficient to model the structural performance of composite plates subject to out-of-plane bending.

Post-deposition heat treatment of co-deposited Cr3C2 and AISI 410 stainless steel using the coaxial laser deposition technique

Cr3C2 ceramic powder is added in varying amounts to AISI 410 stainless steel powder to develop AISI 400 based alloys with varying chromium and carbon content using the coaxial laser deposition technique operating at parameter sets which guarantee full melting of the constituent powder particles. Theoretical isothermal curves for the in situ generated alloys are correlated with the as-deposited and heat-treated microstructures using electron microscopy, X-ray and electron backscatter diffraction techniques. It is concluded that with an increased carbon loading in the mixture, post-deposition heat treatment involving full re-austenitising and tempering is necessary in order to reduce the effect of solute trapping which negatively affects the material mechanical properties.

Characterisation, wear and corrosion testing of laser-deposited AISI 316 reinforced with ceramic particles

Abstract Direct laser deposition was used to create tracks and surfaces using AISI 316 stainless steel powder blended with alumina, tungsten carbide or chromium carbide, with the aim to apply localised reinforcement to stainless steel components. Co-deposition of the powders was carried onto an AISI 316 stainless steel surface to evaluate parameters, and to produce specimens for metallography, EDX and XRD analysis and microhardness tests. Testing of the specimens produced using selected parameters included pin-on-disc wear tests, slurry pot erosion and corrosion testing. The alumina failed to produce a useful improvement to material properties. Tungsten carbide improved wear resistance by 260 times while erosion resistance was doubled; chromium carbide gave a maximum improvement of 88 time to sliding wear resistance, and a 2·3 times maximum improvement of erosion resistance. Chromium carbide-reinforced material furthermore performed well in corrosion tests. The deposition and testing of these materials is described and the outcome of the tests carried out is reported.

Autogenous Laser Keyhole Welding of AISI 316LTi

Effective autogenous full-penetration welding of 4 mm thick AISI 316LTi austenitic stainless steel bars was achieved using a CO2 laser. The welding process parameters required to obtain an optimal and repeatable procedure giving the best quality welds were identified. The use of side jet of gas suppressing plasma formation was investigated, and it was discovered that there are optimal conditions that result in increased power transmission and improved repeatability. Tests were carried out on the final welds in the as-welded state and in the annealed state. These included microstructural and X-ray diffraction (XRD) analysis as well as potentiodynamic and salt spray corrosion tests. Microstructural analysis showed that solidification occurred in primary ferrite solidification (FA) mode. Application of a heat treatment to the welded samples dissolved the ferrite, but resulted in carbide precipitation diminishing resistance to pitting, and the corrosion tests carried out demonstrated that the corrosion-resistant properties of the material were not compromised by the welding process, and that a post-process heat treatment was unnecessary.

Laser surface modification of aluminium and magnesium alloys

Abstract: Aluminium and magnesium alloys are choice materials for research, development and application of surface engineering techniques. Favoured for their low density and ease of fabrication, combined with good mechanical properties, they demonstrate a poor resistance to surface wear; and magnesium alloys are particularly susceptible to corrosion. Due to the flexibility and relative ease of control of laser processing techniques and the limited or negligible effect on the bulk material, the modification of surface properties by means of such methods has been extensively investigated. The range of laser surface processes applied to light alloys includes simple remelting of the alloy surface; remelting with the addition of alloying elements or ceramic particles; cladding with a layer of material having different properties; and shock processing to create residual stresses in the surface.

Direct laser deposition and sliding wear of AISI316/WC10Ni and AISI316/Cr3C2 surfaces

Abstract The deposition of AISI316 stainless steel with tungsten carbide agglomerates and chromium carbide powder was carried out as part of an investigation aimed at determining the feasibility of applying localised reinforcement to stainless steel components. The codeposition of tungsten carbide agglomerates or sintered chromium carbide powder with AISI316 stainless steel powder was carried out to evaluate parameters and produce surfaces for pin on disc wear tests. The wear resistance of the surfaces was improved by the addition of both materials, with the tungsten carbide reinforcement resulting in a higher wear performance while the chromium carbide produced better surface consistency. The deposition and structure of these test pieces are described and the outcome of the tests carried out reported.

Microstructure evaluation of A356 aluminium alloy laser surface alloyed with Ni-Ti-SiC and Ni-Ti-C

Laser surface alloying of A356 aluminium alloy was performed by means of a continuous wave CO2 laser with alloying elements being introduced in the substrate by a stream of powder co-axial to the laser beam. Powder mixtures containing Ni-Ti-SiC and Ni-Ti-C were used to create uniform alloyed surfaces consisting of carbides embedded in a matrix of aluminium with Al-Ni intermetallics. The resulting microstructures were examined by means of optical and scanning electron microscopy, and the various phases were identified by Energy Dispersive X-Ray Spectroscopy and X-Ray Diffraction. Surfaces produced using Ni-Ti-C powders presented a microstructure composed of fine TiC particles dispersed in structures of Al-Ti-Si and Al-Ni intermetallics within an Al-Si matrix. The surfaces produced with Ni-Ti-SiC powder mixtures presented a similar microstructure, with the addition of undissolved SiC particles. The TiC particles in the structures were formed from the in-situ reaction between the carbon or the dissociated SiC and the titanium. The alloyed surfaces gave an increase in hardness compared to the substrate of up to 3.5 times, increasing with the proportion of alloying elements in the structure.Laser surface alloying of A356 aluminium alloy was performed by means of a continuous wave CO2 laser with alloying elements being introduced in the substrate by a stream of powder co-axial to the laser beam. Powder mixtures containing Ni-Ti-SiC and Ni-Ti-C were used to create uniform alloyed surfaces consisting of carbides embedded in a matrix of aluminium with Al-Ni intermetallics. The resulting microstructures were examined by means of optical and scanning electron microscopy, and the various phases were identified by Energy Dispersive X-Ray Spectroscopy and X-Ray Diffraction. Surfaces produced using Ni-Ti-C powders presented a microstructure composed of fine TiC particles dispersed in structures of Al-Ti-Si and Al-Ni intermetallics within an Al-Si matrix. The surfaces produced with Ni-Ti-SiC powder mixtures presented a similar microstructure, with the addition of undissolved SiC particles. The TiC particles in the structures were formed from the in-situ reaction between the carbon or the dissociated Si...