Mithila Achintha

Bio: Mithila Achintha is an academic researcher from University of Southampton. The author has contributed to research in topics: Residual stress & Fibre-reinforced plastic. The author has an hindex of 12, co-authored 53 publications receiving 473 citations. Previous affiliations of Mithila Achintha include University of Manchester & University of Oxford.

Eigenstrain modelling of residual stress generated by arrays of laser shock peening shots and determination of the complete stress field using limited strain measurements

Abstract: This paper presents a hybrid explicit finite element (FE)/eigenstrain model for predicting the residual stress generated by arrays of adjacent/overlapping laser shock peening (LSP) shots where the use of a completely explicit FE analysis may be impractical. It shows that for a given material, the underlying eigenstrain distribution (in contrast to the resulting stress field) representing a laser shock peen is primarily dependent on the parameters of the laser pulse and the number of overlays rather than the precise component geometry. Consequently the residual stress introduced by complex laser peening treatments can be built up by using static FE models and superposition of individual eigenstrain distributions without recourse to further computationally demanding explicit FE analyses. It is found that beneath a small LSP array the magnitude of the compressive residual stress is higher than for a wider array of LSP shots and that with increasing numbers of layers the compressive stress increases as does the depth of the compressive zone. The model predictions for the eigenstrain distributions are compared well with experimental measurements of plastic strain (full-width-at-half-maximum) obtained by neutron diffraction. The eigenstrain method is also extended to construct the full residual stress field using measured residual elastic strains at a finite number of measurement locations in a component.

Field-Assisted Sintering Technology/Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments

Abstract: Field-assisted sintering technology/Spark plasma sintering is a low voltage, direct current (DC) pulsed current activated, pressure-assisted sintering, and synthesis technique, which has been widely applied for materials processing in the recent years. After a description of its working principles and historical background, mechanical, thermal, electrical effects in FAST/SPS are presented along with the role of atmosphere. A selection of successful materials development including refractory materials, nanocrystalline functional ceramics, graded, and non-equilibrium materials is then discussed. Finally, technological aspects (advanced tool concepts, temperature measurement, finite element simulations) are covered.

Laser Peening Process and Its Impact on Materials Properties in Comparison with Shot Peening and Ultrasonic Impact Peening

Abstract: The laser shock peening (LSP) process using a Q-switched pulsed laser beam for surface modification has been reviewed. The development of the LSP technique and its numerous advantages over the conventional shot peening (SP) such as better surface finish, higher depths of residual stress and uniform distribution of intensity were discussed. Similar comparison with ultrasonic impact peening (UIP)/ultrasonic shot peening (USP) was incorporated, when possible. The generation of shock waves, processing parameters, and characterization of LSP treated specimens were described. Special attention was given to the influence of LSP process parameters on residual stress profiles, material properties and structures. Based on the studies so far, more fundamental understanding is still needed when selecting optimized LSP processing parameters and substrate conditions. A summary of the parametric studies of LSP on different materials has been presented. Furthermore, enhancements in the surface micro and nanohardness, elastic modulus, tensile yield strength and refinement of microstructure which translates to increased fatigue life, fretting fatigue life, stress corrosion cracking (SCC) and corrosion resistance were addressed. However, research gaps related to the inconsistencies in the literature were identified. Current status, developments and challenges of the LSP technique were discussed.