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Laser shock peening (LSP) is a relatively novel and promising surface hardening method. An absorbing layer, which is needed to protect the specimen surface from undesirable thermal effects caused by laser irradiation, should be considered as one of many varying parameters. The physical characteristics of the coating and its adhesion to the specimen surface can significantly influence the result of LSP. In this study, three commonly used absorbing coatings, namely black polyvinylchloride tape with a sticky layer, aluminum foil, and black alkyd paint were used to cover three-millimeter-thick plates of the Ti-6Al-4V titanium alloy with globular or lamellar microstructures. LSP of one side of the plates was carried out with a power density of 10 GW/cm2. The hole drilling method was used to evaluate residual stresses. The aluminum foil was found to be the optimal option for LSP of the Ti-6Al-4V titanium alloy. Microstructural investigations carried out using EBSD analysis suggested that no significant reduction in grain size, twinning, or dislocation density growth occurred as a result of LSP irrespective of the initial structure. [ABSTRACT FROM AUTHOR]

The TiNbZr/(Ti, Nb)B metal matrix composite with 2.5 vol.% of borides was produced by vacuum arc melting. The composite was then cold-rolled to thickness strains of 10, 20, 50, or 80%. In the initial condition, the composite had a network-like microstructure consisting of the soft TiNbZr matrix (dendrites) and the rigid (Ti, Nb)B shell (interdendritic space). In comparison with the as-cast condition, cold rolling increased strength by 17–35%, depending on the thickness strain. After the maximum thickness strain of 80%, yield strength and ultimate tensile strength of the composite achieved 865 and 1080 MPa, respectively, while total elongation was found to be 5%. Microstructural analysis revealed that cold rolling to 50% resulted in the formation of crossing shear bands caused by the considerable difference in deformation behavior of the matrix and reinforcements. Cold rolling to 80% led to the formation of a lamellar-like microstructure comprising the interlayers of the (Ti, Nb)B phase between the TiNbZr laths. The maximum strain (80% cold rolling) shortened the (Ti, Nb)B fibers into nearly equiaxed particles, with a length to diameter ratio of ~2. [ABSTRACT FROM AUTHOR]

The experimental study of heat flux evolution at the fatigue crack tip during biaxial loading was carry out in this work. The plane samples of stainless steel AISI 304 with thick of 3 mm were weakened by notch to initiate fatigue crack at the centre of samples. A contact heat flux sensor based on the Seebeck effect was used to monitor the dissipated thermal energy. During tests the samples were subjected to cyclic loading of 5 Hz with constant stress amplitude and different biaxial parameter. The experimental results confirm the previous conclusions of authors about two regime of energy dissipation at fatigue crack tip. The curve of the dissipated energy can be divided in two stages. In the second stage is characterized by classical linear relation between crack rate and energy dissipation. In the first stage the crack rate is proportional to the multiplication of the power of heat flux by crack length. The energy dissipation does not depend on the biaxial parameter during cyclic loading.

Pulsed thermography is an active non-destructive technique which uses optical excitation source to stimulate heating of the object under investigation. This work is devoted to the simulation of the pulsed thermography method in a steel plate with a ceramic coating containing artificial defects of various depths and sizes. The simulation has been carried out on the base of a model which takes into account complex heat exchange of the sample with the surrounding by convection, conduction and radiation. Comparison of the temperature contrast with the experimental data has shown that the results are in a good qualitative and quantitative agreement in all stages of the cooling process. Due to the fact that the temperature contrast is often susceptible to surface noise of various nature the Kalman-based signal processing technique was developed. The comparative analysis has shown that the proposed filtration technique provides a better signal-to-noise ratio in comparison to the considered well-known techniques of signal reconstruction when proper calibration of the filtration parameters is carried out. [ABSTRACT FROM AUTHOR]

The study of energy balance at crack tip could give comprehensive information for estimation of durability and reliability cracked construction under cyclic loading. The first step for estimation energy balance is monitoring of dissipated part of energy (heat generation). One of the most effective techniques for investigation of temperature evolution on the surface of deformed body is infrared thermography. The work is devoted to the experimental study of energy dissipation in cracked samples made of titanium Grade 2 under multiaxial cyclic loading. To explain the experimentally obtained correlation between fatigue crack rate and power of heat dissipation we developed a phenomenological model describing the evolution of plastic work at the crack tip under arbitrary loading. The theoretical and experimental data about heat dissipation exhibit a good quantitative agreement. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies investigating fatigue crack growth were conducted on flat samples made of stainless steel AISE 304 and titanium alloy Grade 2. The heat flux from the crack tip caused by plastic deformation localization was measured using the contact heat flux sensor previously developed by the authors. This provides a possibility to find a correlation between energy dissipation and crack propagation rate under fatigue uniaxial loading with constant stress intensity factor and under biaxial loading with constant stress amplitude. The experiments with constant stress intensity factor have shown a decrease in energy dissipation at constant crack rate and stress ratio R=σmin/σmax=-1 (R=0). A theoretical analysis of the stress field at the fatigue crack tip has been carried out to explain this phenomenon. Based on the obtained results, the heat flux from the crack tip is represented as the sum of two functions describing energy dissipation in monotonic and reversible plastic zones separately. It has been shown that dissipation in a reversible plastic zone is a function of the applied stress amplitude only. This causes a decrease of energy dissipation at constant stress intensity factor. The proposed phenomenology was successfully verified by testing both materials under biaxial loading. [ABSTRACT FROM AUTHOR]

The work is devoted to experimental study of heat flux evolution at the fatigue crack tip during biaxial loading with a goal to relate the heat flux to the rate of crack propagation under different loading conditions. The plane samples of titanium alloy (Grade 2) 1 mm thick were weakened by notch to initiate fatigue crack at their centers. Infrared thermography and the contact heat flux sensor, which is based on the Seebeck effect, were used to monitor the dissipated thermal energy. The samples were subject to cyclic loading with constant stress amplitude at different biaxial coefficients. The experimental results confirmed the previous conclusions of the authors about two regime of energy dissipation at fatigue crack tip under Paris regime. At the first stage, the power of heat flux is proportional to the product of the crack rate by the crack length. The second stage is characterized by a traditional linear relationship between the crack rate and the heat flux. [ABSTRACT FROM AUTHOR]