C. Correa

Thermomechanical modelling of stress fields in metallic targets subject to laser shock processing

Purpose – Laser shock peening (LSP) is mainly a mechanical process, but in some cases, it is performed without a protective coating and thermal effects are present near the surface. The numerical study of thermo‐mechanical effects and process parameter influence in realistic conditions can be used to better understand the process.Design/methodology/approach – A physically comprehensive numerical model (SHOCKLAS) has been developed to systematically study LSP processes with or without coatings starting from laser‐plasma interaction and coupled thermo‐mechanical target behavior. Several typical results of the developed SHOCKLAS numerical system are presented. In particular, the application of the model to the realistic simulation (full 3D dependence, non‐linear material behavior, thermal and mechanical effects, treatment over extended surfaces) of LSP treatments in the experimental conditions of the irradiation facility used by the authors is presented.Findings – Target clamping has some influence on the re...

Laser Shock Processing: an emerging technique for the enhancement of surface properties and fatigue life of high-strength metal alloys

Profiting by the increasing availability of laser sources delivering intensities above 10 9 W/cm 2 with pulse energies in the range of several Joules and pulse widths in the range of nanoseconds, laser shock processing (LSP) is being consolidating as an effective technology for the improvement of surface mechanical and corrosion resistance properties of metals and is being developed as a practical process amenable to production engineering. The main acknowledged advantage of the laser shock processing technique consists on its capability of inducing a relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly, the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Following a short description of the theoretical/computational and experimental methods developed by the authors for the predictive assessment and experimental implementation of LSP treatments, experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (specifically steels and Al and Ti alloys) under different LSP irradiation conditions are presented

Induction of engineered residual stresses fields and enhancement of fatigue life of high reliability metallic components by laser shock processing

Laser shock processing (LSP) is being increasingly applied as an effective technology for the improvement of metallic materials mechanical and surface properties in different types of components as a means of enhancement of their corrosion and fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, follow-on experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys characteristic of high reliability components in the aerospace, nuclear and biomedical sectors) under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies. Additional remarks on the improved character of the LSP technique over the traditional “shot peening” technique in what concerns depth of induced compressive residual stresses fields are also made through the paper.

Fatigue life enhancement of high reliability metallic components by laser shock processing

Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials mechanical properties in different types of components as a means of enhancement of their mechanical behavior. As reported in the literature, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, experimental results on the residual stress profiles and associated mechanical properties modification successfully reached in typical materials under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies. In this case, the specific behavior of a widely used material in high reliability components (especially in nuclear and biomedical applications) as AISI 316L is analyzed, the effect of possible “in-service” thermal conditions on the relaxation of the LSP effects being specifically characterized.

9.04 – Laser Plasma Interaction and Shock Material Processing

Laser shock processing (LSP) is based on the application of a high-intensity pulsed laser beam (I > 109 W cm−2; τ < 50 ns) on a metallic target, forcing a sudden vaporization of its surface into a high-temperature and density plasma that immediately develops, inducing a shock wave propagating into the material. Although several authors have contributed significant work through experiments that explore the optimum conditions of application of the treatments and to assess their ultimate capability to provide enhanced mechanical behavior to workpieces of typical materials, only limited attempts have been developed in the way of full comprehension and predictive assessment of the characteristic physical processes and material transformations with a specific consideration of real material properties. A fundamental reason for the referred lack of predictive capability of LSP processes is their inherent physical complexity, especially stemming from the coexistence of different material phases (including plasma) developing and interacting under the action of the high-intensity laser beam. This particular situation, which is not very common in classical high-power laser applications, poses the need for the development of comprehensive analysis and prediction tools enabling an integrated comprehension of the physical phenomena developing in the process and their mutual interrelations. Provided the large amount of physical phenomena arising in the considered processes, the corresponding modeling, including the formation of a vapor/plasma phase, the generally far from equilibrium ionization–recombination processes in this plasma, its thermo-fluid dynamic behavior under extreme pressure and temperature conditions (typically leading to pressure/shock waves), etc., requires a deep understanding of the physics underlying their appearance, and is absolutely needed for the reliable predictive assessment of the material evolution under irradiation. This is the basic reason for the need of calculation tools providing a more complete treatment of laser shock processing than the methods that only deal with analysis of shock wave propagation in the materials according to simplified models. The present article presents a review of the physical issues dominating the development of LSP processes from a high-intensity laser–matter interaction point of view, along with the theoretical and computational methods developed by the authors for their predictive assessment. Practical results at laboratory scale on the application of the technique to different materials are shown, along with corresponding results on the mechanical properties improvement induced by LSP treatments.

Computer-Aided Development of Thermo-Mechanical Laser Surface Treatments for the Fatigue Life Extension of Bio-Mechanical Components

Bio-mechanical components (i.e. spinal, knee and hip prostheses) are key elements definitely improving the quality of life of human beings. These components development has been traditionally subject to mechanical and functional designs based primarily on intuitive medical approaches, not always optimized from an engineering point of view, what in turn has been responsible for undesirable cases of mechanical failure implying the need for additional surgical interventions and its associate life risk for aged patients. Laser Shock Processing (LSP) uses the high peak power of short pulse lasers to generate an intense shock wave into the material finally leading to the generation of a compressive residual stresses field definitely protecting the component against crack initiation and propagation, thus improving its mechanical response and in-service fatigue life. Developments in the field of the predictive assessment of LSP are presented along with practical examples of the design-motivated improvements in prostheses achievable by LSP.

Induction of through-thickness compressive residual stress fields in thin Al2024-T351 plates by laser shock processing

Purpose – With the aid of the calculational system developed by the authors, the analysis of the problem of laser shock processing (LSP) treatment for induction of residual stress (RS) fields for fatigue life enhancement in relatively thin sheets in a way compatible with reduced overall workpiece deformation due to spring-back self-equilibration has been envisaged. Numerical results directly tested against experimental results have been obtained confirming the critical influence of the laser energy and irradiation geometry parameters. The paper aims to discuss these issues. Design/methodology/approach – Plane rectangular specimens (160 mm×100 mm×2 mm) of Al-cladded (∼80 μm) Al2024-T351 were considered both for LSP experimental treatment and for corresponding numerical simulation. The test piece is fixed on a holder and is driven along X and Y directions by means of an anthropomorphic robot. The predefined pulse overlapping strategy is used for the irradiation of extended areas of material. From the geomet...

Numerical modelling and experimental implementation of laser shock micro-forming of thin metal sheets

Continuous lasers have been extensively used for macroscopic metal sheet forming. However, for the manufacturing of micro–mechanical systems, the applicability of such type of lasers is limited by the long relaxation time of the thermal fields responsible for the forming phenomena, what makes the generated internal residual stress fields more dependent on ambient conditions. The use of short pulse (ns) lasers provides a suitable parameter matching for the laser forming of an important range of sheet components used in MEMS as the short interaction time in this case allows a faster predominantly mechanical effect. In the present paper, laser shock micro–forming (LSμF) is presented as an emerging technique for microsystems parts shaping and adjustment along with a discussion on its physical foundations and practical implementation possibilities developed by the authors.

Effect of Thermal Treatments on the Mechanical Properties Enhancement of High Reliability Metallic Materials by Laser Shock Processing

Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials mechanical properties in different types of components as a means of enhancement of their fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses fields into metallic components allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, experimental results on the residual stress profiles and associated mechanical properties modification successfully reached in typical materials under different LSP irradiation conditions are presented. In this case, the specific behavior of a widely used material in high reliability components (especially in nuclear and biomedical applications) as AISI 316L is analyzed, the effect of possible “in-service” thermal conditions on the relaxation of the LSP effects being specifically characterized.

Mechanical Properties Enhancement of High Reliability Metallic Materials by Laser Shock Processing

Laser shock processing (LSP) is being increasingly applied as an effective technology for the improvement of metallic materials surface properties in different types of components as a means of enhancement of their corrosion and fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, follow-on experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys) under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies and the evaluation of the corresponding induced properties as material specific volume reduction at the surface, microhardness and wear resistance. Additional remarks on the improved character of the LSP technique over the traditional “shot peening” technique in what concerns depth of induced compressive residual stresses fields are also made through the paper.