Shock Processing Research Articles

Thermal stability study of TC11 titanium alloy thin component after surface nanocrystallization induced by laser shock processing

Laser shock peening (LSP) can induce the compressive residual stress (CRS) on the surface of the material, and surface nanocrystallization can be realized with a nanocrystal layer, thereby significantly improving the high-cycle fatigue performance. However, due to weak material constrain and the high working temperature of thin aero-engine compressor blades, CRS and refined grain structure are more likely to result in stress relaxation and microstructural recovery under thermal stress load, resulting in reducing the anti-fatigue effect of LSP. In this paper, on the basis of the surface nanocrystallization induced by LSP, residual stress and microstructure of TC11 titanium alloy thin components were measured and observed. The residual stress relaxation was characterized and the microstructure evolution was discussed. Also, the thermal stability mechanism of CRS and the nanostructure on the surface were analyzed. The experimental results show that after thermal loads, the CRS was decreased, and the stress relaxation amplitude was increased with an increase in temperature. After annealing at 400 °C, the dislocation density was significantly reduced, but the grain sizes of surface nanostructure did not greatly increase. After annealing at 400 °C for 2 h, the fatigue strength of the LSPed specimen was reduced compared with that before annealing, but it was still increased compared with the original state without LSP, especially under high-power density for multiple LSP treatment. It can be concluded that the surface nanostructure has good stability and effectively retards the initiation of fatigue cracks on the surface, which ensures the effectiveness of LSP under thermal loads.

ПРИМЕНЕНИЕ ИСКУССТВЕННОЙ НЕЙРОННОЙ СЕТИ ПРИ МОДЕЛИРОВАНИИ ТЕХНОЛОГИИ ЛАЗЕРНО-УДАРНО-ВОЛНОВОЙ ОБРАБОТКИ МАТЕРИАЛОВ

The technology of laser shock processing (LSP) is an innovative surface modification technology using generated fields of compressive residual stresses (CRS) in the near-surface region of the materials under study. In this work, a new method based on an artificial neural network (ANN) is used to predict residual stresses and microhardness in the Ti-6Al-4V titanium alloy processed using the LSP technology. It is shown that ANN is a reliable method for predicting the mechanical properties of materials processed using the LSP technology, in the presence of limited experimental data.

A maintenance strategy based on system reliability considering imperfect corrective maintenance and shocks

In this study, an innovative maintenance strategy is proposed for systems subject to normal degradation and shock process. The shock process is a non-homogeneous Poisson process, and a changing factor is considered for the dependence between the normal degradation and the occurrence intensity of shocks. The system reliability is divided into three stages, based on which maintenance activities are implemented. In Stage 1 and Stage 2, when a fatal shock occurs, corrective maintenance is performed if the number of completed corrective maintenance activities does not reach the allowed limit; Otherwise, the system is replaced. Replacement is always performed once the system reliability decreases to Stage 3. Corrective maintenance is imperfect, with a perfect or minimal effect at certain probabilities. Two control variables, the allowed numbers of corrective maintenance in Stage 1 and Stage 2, are determined to minimize the expected system cost rate, by using Particle Swarm Optimization algorithm. The proposed model and method are illustrated by an example of one sliding spool. The optimal result is verified by checking the results of feasible variables. Furthermore, the proposed maintenance policy is compared with two contrastive maintenance policies. The comparison results show the necessity and effectiveness of the proposed method.

Corrosive-wear behavior of LSP/MAO treated magnesium alloys in physiological environment with three pH values

Abstract A laser shock peening (LSP) layer, a micro-arc oxidation (MAO) coating, and an LSP/MAO composite coating were fabricated on the surface of AZ80 magnesium alloy by laser shock and micro-arc oxidation process. The ball-disc grinding method was used to perform wear test on the three treated specimens in simulated body fluids (SBF) with pH values of 4, 7.4 and 9. The morphology and element content of worn surface were investigated by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results indicated that the wear rates of the three treated specimens in three pH environment in numerical order were pH 4 > pH 7.4 > pH 9, respectively. The wear rates of the three treated specimens in the same pH environment were arranged in the order of MAO > LSP > LSP/MAO, respectively. The main wear mechanisms of the LSP specimen in pH 4 environment were fatigue wear and corrosion wear, while it were corrosion wear and adhesive wear in pH 7.4 and pH 9 environments. Abrasive wear, fatigue wear and corrosion wear were the main wear mechanisms of the MAO specimen in pH 4 environment, while abrasive wear, adhesive wear and corrosion wear were the main wear mechanisms of that in pH 7.4 and pH 9 environments. The corrosion wear resistance of the LSP/MAO specimen in SBF solution with three pH values was improved due to the synergism of LSP fine crystal layer and MAO coating.

Features of Using Cryogenic Laser Shock Processing for Hardening of 2024-T351 Aluminum Alloys

Features of Using Cryogenic Laser Shock Processing for Hardening of 2024-T351 Aluminum Alloys

Anisotropy of Residual Stresses Occurring upon Laser Shock Processing of the 2024-T351 Aluminum Alloy and Ways to Reduce It

Anisotropy of Residual Stresses Occurring upon Laser Shock Processing of the 2024-T351 Aluminum Alloy and Ways to Reduce It

Investigation on failure mechanism of the absorption film subjected to double-sided laser shock processing

In this paper, the failure mechanism of the absorption film (AF) subjected to double-sided laser shock processing (DSLSP) was investigated. The propagation of laser-induced stress wave in the multilayer material and the deformation process of the AF were analyzed with finite element method, and the corresponding experiments were carried out to verify the calculated results. The three-dimensional topographies of the shocked AF and the substrate were measured, and scanning electron microscope (SEM) was also used to observe the irradiated surface. The investigations show that the transmission and reflection of stress waves in the multilayer material produce outward stretching effect on the AF, which attempts to divorce the AF from the substrate. The AF bulges from the substrate with damped oscillation if the intensity of divorced stress wave exceeds the adhesion strength between them, and the shallow depressed crater is also left on the surface of substrate simultaneously. If the multiple DSLSP proceeds on the bulged AF, it ruptures and loses the protection to the substrate.

Dolomites in hydrated fine-grained Antarctic micrometeorites: Effective tools for analyzing secondary processes

We report detailed transmission electron microscope (TEM) observations of carbonates from one hydrated fine-grained Antarctic micrometeorite (H-FgMM). These carbonates show the occurrence of complex chemical variations and microstructures that provide important evidence regarding the formation and evolution of rarely analyzed H-FgMMs. The chemical variations were identified at both micrometer and nanometer scales, indicating that these carbonates formed under localized fluid conditions that suggest a variable chemical microenvironment. Individual carbonates grew from isolated reservoirs of fluid. Moreover, these carbonates contain manganese amounts almost twice as high as those measured in CM chondrites but similar to those identified in CI chondrites. Their particular compositions indicate reducing and progressively evolving conditions in the fluid from which these carbonates precipitated, probably due to water consumption during phyllosilicates formation. In addition to the compositional variability, microstructural features are pervasive in these carbonates, similar to those described in heavily shocked meteorites indicating that these carbonates were probably modified during shock processes after their formation. Since carbonates are highly susceptible to shock metamorphism, we suggest that it is essential to investigate their structure in detail before interpreting the isotopic measurements related to the time of their formation. Additionally, associated with carbonates, ubiquitous phosphates were identified in the micrometeorite analyzed. Future studies of these mineral associations will provide us further insight into the formation and evolution of asteroids, especially since they were both identified in the surface materials of Ryugu and Bennu.

The role of direct peritoneal resuscitation in the treatment of hemorrhagic shock after trauma and in emergency acute care surgery: a systematic review.

Direct peritoneal resuscitation (DPR) has been used to help preserve microcirculation by reversing vasoconstriction and hypoperfusion associated with the pathophysiological process of shock, which can occur despite appropriate intravenous resuscitation. This approach depends on infusing a hyperosmolar solution intraperitoneally via a percutaneous catheter with the tip ending near the pelvis or the root of the mesentery. The abdomen is usually left open with a negative pressure abdominal dressing to continuously evacuate the infused dialysate. Hypertonicity of the solution triggers visceral vasodilation to help maintain blood flow, even during shock, and is also associated with reduced local inflammatory cytokines and other mediators, preservation of endothelial cell function, and mitigation of organ edema and necrosis. It also has a direct effect on liver perfusion and edema, more rapidly corrects electrolyte abnormalities compared to intravenous resuscitation alone, and may requireless intravenous fluid to stabilize blood pressure, all of which shortens the time required to close patients' abdomen. An online query using the search term "direct peritoneal resuscitation" was carried out in PubMed, MEDLINE and SciELO, limited to publications indexed from January 2014 to June 2020. Of the 20 articles returned, full text was able to be obtained for 19. A manual review of included articles' references was resulted in the addition of 1 article, for a total of 20 included articles. The 20 articles were comprised of 15 animal studies, 4 clinical studies,and 1 expert opinion. The benefits include both local and possibly systemic effects on perfusion, hypoxia, acidosis, and inflammation, and are associated with improved outcomes and reduced complications. DPR shows promise in patients with hemorrhagic shock, septic shock, and other conditions resulting in an open abdomen after damage control laparotomy.

Theoretical lifetimes and Stark broadening parameters for visible-infrared spectral lines of V i in Arcturus

ABSTRACT In this work, the Stark broadening parameters (line widths and line shifts) of 114 visible-infrared spectral lines of neutral vanadium (V i) have been calculated. As in a previous work devoted to their spectral lines in the Ultraviolet (UV)-blue range, these parameters have been calculated using the Griem’s semi-empirical formula and the Cowan code for the calculation of the necessary matrix elements. In addition to their astrophysical interest (the majority of the analysed spectral lines have been detected in Arcturus, in the metal-poor star HD 84937 and in the Sun), these parameters are also relevant in the analysis of plasmas generated in industrial processes in Laser Shock Processes treatments of Ti-6Al-4V type samples.

An empirical test of a fundamental Harrod-Kaldor business cycle model

Going back to the roots of modern business cycle modelling, the paper advances a macroeconomic model of a most elementary (and now largely forgotten) cycle mechanism within a growth framework. Essentially, it combines a nonlinear Harrodian instability for a business sentiment index with Harrod’s and Kaldor’s old idea that firms tend to reduce investment if they have already built up high capacities relative to their assessment of the normal market potential. For greater realism, a previous version is augmented by a delay in the capital growth rate and by in general three random shock processes. This makes it possible to estimate the model on quarterly US data of utilization and a certain capital ratio. The focus is on an inquiry into the model’s goodness-of-fit, for which the method of simulated moments is a fruitful technique. Here, 14 fairly ambitious summary statistics that the model should try to reproduce allow a detailed diagnosis of its merits and demerits. The results are sufficiently encouraging and form a sound basis for stepwise extensions of the model in future work, or for refinements in the estimation procedure.

Effects of Thermally Assisted Warm Laser Shock Processing on the Microstructure and Fatigue Property of IN718 Superalloy

Effects of Thermally Assisted Warm Laser Shock Processing on the Microstructure and Fatigue Property of IN718 Superalloy

Experimental Study on FGH95 Superalloy Turbine Disk Joint Material by Oblique Laser Shock Processing

The FGH95 superalloy used for turbine disk manufacturing was strengthened by the oblique laser shock processing (OLSP). The laser energy, beam diameter, and number of impacts were selected as the test factors, and the three-factor three-level oblique laser shock processing orthogonal test was carried out. Based on the analysis of variance and range of the surface residual stress, microhardness, roughness, tensile strength, and yield strength of FGH95 superalloy after LSP, the factor level combination of relative best comprehensive performance was obtained. The results showed that, within the 10% confidence level, the order of influencing factors with significant difference is: laser energy > number of impacts > beam diameter. Compared with the unimpacted sample, the microhardness of the material surface was increased by about 25% after OLSP. With the increase of laser energy, the dimple distribution of the sample was more uniform, smaller in size, and shallower in depth. However, the thickness of the affected layer was very low, and there was no significant effect on the tensile properties. In general, and under the test conditions selected in this study, the combination of 8 Joule laser energy, 3 mm beam diameter, and three impacts can be selected to obtain the best comprehensive performance. The results of this paper provide a reference for the OLSP of the FGH95 superalloy turbine disk and other aero engine parts.

Extrapolation of Almen Control to Laser Shock Processing

Extrapolation of Almen Control to Laser Shock Processing

Learning efficiency shocks, knowledge capital and the business cycle: A Bayesian evaluation

AbstractWe incorporate shocks to the efficiency with which firms learn from production activity and accumulate knowledge into an otherwise standard real DSGE model with imperfect competition. Using real aggregate data and Bayesian inference techniques, we find that learning efficiency shocks are an important source of observed variation in the growth rate of aggregate output, investment, consumption and especially hours worked in post‐war US data. The estimated shock processes suggest much less exogenous variation in preferences and total factor productivity are needed by our model to account for the joint dynamics of consumption and hours. This occurs because learning efficiency shocks induce shifts in labour demand uncorrelated with current total factor productivity (TFP), a role usually played by preference shocks that shift labour supply. At the same time, knowledge capital acts like an endogenous source of productivity variation in the model. Measures of model fit prefer the specification with learning efficiency shocks. The results are robust to the addition of many observables and shocks.

Research on the forming and strengthening mechanism and performance thermal stability of microstructures induced by laser shock imprinting

Laser shock processing can induce a large number of dislocations in metal crystals by producing ultra-high strain rate deformations. This study investigated the mechanism and process of dislocation strengthening and the various dislocation configurations that play strengthening roles. The materials in this experiment were heat-treated in accord with the annealing strengthening mechanism, and the surface morphology, hardness, surface roughness, and corrosion resistance of the formed microstructure were measured and characterized, the amount of change were within 10%, which proved that the mechanical and physical properties were not degraded. Considering the possibility of using laser shock imprinting (LSI) manufacturing for actual production, the target parameters in the experiment were optimized, and it was found that with an appropriate molding depth ratio, the microstructure could be fully formed without deformation of the back surface. This discovery allowed the formed microstructure to withstand a greater axial load. Then, the changes and stress conditions in the target material during the forming process for targets with different thicknesses were explored. Finally, the prepared microstructures were used in hot embossing experiments, and the microstructures were perfectly transferred to the polymer surface, proving that the microstructures prepared by LSI have the potential to work under high-temperature and high-pressure scenarios.

Observing the prevalence of thin current sheets downstream of Earth's bow shock

Actively reconnecting, thin current sheets have been observed both within the transition region of Earth's bow shock and far downstream into the magnetosheath. Irrespective of whether these structures arise due to shock processes or turbulent dissipation, they are expected to contribute to particle heating and acceleration within their respective regions. In order to assess the prevalence of thin current sheets in the magnetosheath, we examine shock crossings and extended magnetosheath intervals recorded by the magnetospheric multiscale mission (MMS). For each magnetosheath interval, we quantify the prevalence of current sheets in that region of space using: a one-dimensional measure of structures per unit length of observed plasma, a packing factor corresponding to the fraction of time the spacecraft are within current structures, and a three-dimensional measure requiring an estimate of the number of current sheets within an associated volume. We estimate that volume by considering the three-dimensional cone over which Alfvén and magnetoacoustic waves can propagate during each interval. Using 25 extended magnetosheath intervals observed by MMS, we perform our analysis for different locations in the magnetosheath and for different solar wind conditions. We find that the number density of current sheets is higher toward the magnetosheath flanks, that it reduces as a power law with distance from the bow shock, and that it is not strongly influenced by the properties of the upstream bow shock.

Microstructure Evolution and Properties of Gradient Nanostructures Subjected to Laser Shock Processing in 300M Ultrahigh‐Strength Steel

Herein, gradient nanostructures (GNs) are created in 300M ultrahigh‐strength (UHS) steel by laser shock processing (LSP). Microstructure evolution and properties of GNs subjected to LSP with different pulse energies are thoroughly characterized on 3D profiler, scanning electron microscope (SEM), transmission electron microscope (TEM), X‐ray diffractometer (XRD), X‐ray stress analyzer, nanoindenter, and tensile tester. Results show successful creations of GNs in 300M steel after LSP treatments. With the increase in pulse energy, the size of the surface layer is refined from 15 nm (3 J) to 10 nm (7 J), and the corresponding grains are amorphized to some extent. Meanwhile, many substructure defects such as dislocation tangles and deformation twins (DTs) are noted in the subsurface. The dislocation density and the number of DTs increase with the pulse energy. Further, the high compressive residual stress is introduced to the 300M steel surface after LSP, and the corresponding hardness is improved substantially. The compressive residual stress, depth of the affected layer, and the hardness rise significantly with the pulse energy. Apart from improvements in strength and plasticity, the fracture morphology is changed from a typical ductile fracture to quasicleavage and ductile mixed fracture.

Structural Breaks in an Endogenous Growth Model

Abstract We study the effects of parameter uncertainty prompted by structural breaks. In our model, agents respond differently to uncertainty prompted by regime shifts in shock processes than they react to comparable perceived increases in shock volatility. The magnitude of the response to an increase in uncertainty about TFP associated with a structural break is greater than that of a response to a comparable perceived rise in volatility. This is because lifetime utility varies more when shocks shift beliefs and perceived wealth.

Failure rate-based models for systems subject to random shocks

Shock process that can increase the failure rate of the systems working under a stochastic environment is known as the shot-noise process. In the existing literature focusing on the shot-noise process, it is usually assumed that the failure rate increments caused by shocks are the same constants or identically distributed variables. However, such an assumption has limitations if the external environment is constantly changing or the shocks can weaken the system gradually. This article proposes an extended shock model in which the failure rate increments of systems caused by shocks need not be identical or identically distributed. The reliability functions of the systems as well as some reliability indices are derived explicitly. Some special cases are discussed. Besides, a preventive maintenance model is also investigated in which the system is replaced when the number of shocks reaches a fixed threshold. Finally, an example on a refrigeration system is provided to illustrate the proposed model.