Shock Processing Research Articles

Optimal preventive replacement policy for homogeneous cold standby systems with reusable elements

The paper considers homogeneous, cold standby systems performing missions of the fixed duration when a failure of an operating element results in a mission failure. A system is operating in a random environment modeled by the Poisson process of shocks. Each shock decreases the remaining lifetime of an operating element and, therefore, its preventive replacement using available standby element is scheduled on experiencing the predetermined number of shocks. The crucial feature of the proposed model is that the preventively replaced elements can be used afterwards as the future standby elements. The replacement is not perfect, and its probability of success decreases with the number of replacements. The number of shocks triggering elements’ replacements that maximizes the mission success probability is obtained. A numerical example with detailed analysis is presented.

Effects of oxidation on pyroxene visible-near infrared and mid-infrared spectra

Pyroxene spectral features in the visible near-infrared (VNIR) and mid-infrared (MIR) wavelengths are affected by oxidation resulting from traditional metamorphic processes as well as impact metamorphism. The observed effects are due to modifications in the crystal arising from changes in crystallization temperature or pressure or from substituting Fe3+ for Fe2+. Highly oxidized pyroxenes from terrestrial mantle xenoliths and shock experiments indicate that the spectral effects of oxidation are greater in clinopyroxene than orthopyroxene because clinopyroxene can accommodate more Fe3+ structurally. Changes in clinopyroxene VNIR related to increasing oxidation include a shift in the 0.8 μm absorption band to shorter wavelengths and a strengthening of the Fe2+↔Fe3+ intervalence charge transfer (IVCT) band, which reduces the band depth of the 1.0 μm feature by ~20%. Although shocked clinopyroxenes are oxidized to similar levels to that seen in the mantle xenoliths, the effects of shock overprint those of oxidation in the VNIR. These include a decrease of ~76% intensity of the 2.35 μm feature and a decrease of ~70% intensity of the 1.0 μm feature. In the MIR, the effects of oxidation and shock are minimal, resulting in a 5% overall decrease in band depth. These shifts and changes can be interpreted as a result of changes in the polyhedra surrounding the Fe cations which reduce crystal field splitting and the order of the crystal structure. Determination of planetary surface composition through VNIR remote sensing methods requires careful consideration of potential changes induced via shock and/or oxidation processes.

State-based mission abort policies for multistate systems

Most of the previous research on optimal mission abort policies was devoted to binary systems that can be only in two states, i.e., operable or failure. However, a wide class of engineering systems is characterized by more than one operable state. Thus, it can be reasonable to terminate a mission and initiate a rescue procedure that can save, e.g., costly or safety-critical systems when a system had deteriorated to a certain extent. A system operates in a random environment modeled by a renewal process of shocks. With each shock, the state of a system can deteriorate with certain probabilities that can eventually result in the total failure. The bivariate constrained probability-wise and cost-wise optimization problems are formulated and the necessary relationships for solving them are derived. The detailed illustrative numerical example is discussed.

The effect of high voltage electric shock on the quality attribute of carp fish (Cyprinus carpio) meat

Carp is one of the commercial freshwater fish and requires good preservation to maintain the quality of the meat. The non-thermal food preservation method that is still being developed is by using a high voltage electric shock or often called Pulse Electric Field (PEF). The research on the treatment of electric shock using PEF on carp meat has been done. This study aimed to measure the effect of high voltage electric shock on the quality of the carp fish meat. Fresh carp meat fillets were given exposure to electric shock (30 kV, 60 kV, and 90 kV; frequency 50 Hz; pulse width 0.4 s; 600 pulses) when compared with untreated as a control. The data of log total plate count (TPC) and other quality attributes were analyzed by ANOVA and advanced test with Honesly Significance Different (HSD), while non-parametric data were analyzed using Kruskal-Wallis and Mann-Whitney test. The result showed that in untreated meat fish, the log of TPC is higher than threated meat and significantly different (P < 0.05) at untreated with the treated samples. The electric shock treatment caused temperature increment from 3.3+0.7°C until 5.6+1.3°C but not significantly different between samples. Moisture content decreased significantly due to high voltage electric shock treatment. pH values ranged from 6.46+0.20 to 6.62+0.23 and were not significantly different between treatment. Meat with electric shock treated showed significantly different (P<0.05) on weight loss but not in cooking loss. There are no significant differences in hedonic value except tenderness with 60kV. On the microstructure, the treated meat looks more porous than untreated meat. It is indicating that high voltage electric shock processing was effective in the maintenance of carp meat qualities.

Enhancement of Material Crack Resistance Using Laser Shock Processing

In this paper, we develop a numerical model that allows predicting the effect of laser shock processing of materials on the occurrence of new cracks, as well as on the propagation pattern of existing cracks. Linear cracks and so-called V-shaped cracks are studied. The fields of residual stresses arising during laser shock processing are determined. The optimal modes of laser shock processing in terms of the maximal deceleration of the propagation velocity of the cracks are revealed. The results obtained are in good agreement with the experimental data.

Fatigue life and fracture evolution of small-hole specimens by laser shock processing

The fatigue life and fracture characteristics of aluminum alloy small-hole specimens by laser shock processing (LSP) at different external loads were investigated. When the maximum load was 165.8 MPa, 195 MPa and 275.4 MPa, the median fatigue life gain by LSP was 3.77–4.21 times, 2.68–3.02 times and 1.77–2.20 times, respectively. The plastic deformation zone and residual stress distribution produced by LSP can restrain or control the initiation and propagation direction of cracks. It has been observed that the resulting fracture evolution depends on the applied external load. The stress simulation method, fracture morphology analysis are also used to establish the residual stress distribution, the crack propagation mode and its corresponding relationship with fatigue gain.

Preservation of primordial signatures of water in highly-shocked ancient lunar rocks

Spurred by the discovery of water in lunar volcanic glasses about a decade ago, the accessory mineral apatite became the primary target to investigate the abundance and source of lunar water. This is due to its ability to contain significant amounts of OH in its structure, along with the widespread presence of apatite in lunar rocks. There is a general understanding that crustal cumulate rocks of the lunar magnesian (Mg) suite are better candidates for recording the original isotopic compositions of volatile elements in their parental melts compared to eruptive rocks, such as mare basalts. Consequently, water-bearing minerals in Mg-suite rocks are thought to be ideal candidates for discerning the primary hydrogen isotopic composition of water in the lunar interior. Mg-suite rocks and most other Apollo samples that were collected at the lunar surface display variable degrees of shock-deformation. In this study, we have investigated seven Apollo 17 Mg-suite samples that include troctolite, gabbro and norite lithologies, in order to understand if shock processes affected the water abundances and/or H isotopic composition of apatite. The measured water contents in apatite grains range from 31 to 964 ppm, with associated δD values varying between −535 ± 134‰ and +147 ± 194‰ (2σ). Considering the full dataset, there appears to be no correlation between H2O and δD of apatite and the level of shock each apatite grain has experienced. However, the lowest δD was recorded by individual, water-poor (<∼100 ppm H2O) apatite grains that are either directly in contact with an impact melt or in its proximity. Therefore, the low-δD signature of apatite could be a result of interactions with D-poor regolith (solar wind derived H), facilitated by shock-induced nanostructures that could have provided pathways for migration of volatiles. In contrast, in relatively water-rich apatites (>∼100 ppm H2O), regardless of the complexity of the shock-induced nanostructures, there appears to be no evidence of water-loss or alteration in their δD. The weighted average δD value of 24 such water-rich apatites is −192 ± 71‰, and, of all 36 analyzed spots is −209 ± 47‰, indistinguishable from that of other KREEPy lunar lithologies or the Earth's deep mantle. Despite experiencing variable degrees of shock-deformation at a later stage in lunar history, water-rich apatite in some of the earliest-formed lunar crustal material appears to retain the original isotopic signature of H in the Moon.

Laser Shock Processing and Related Phenomena

Laser Shock Processing (LSP) is continuously developing as an effective technology for improving the surface and mechanical properties of metallic alloys and is emerging in direct competition with other established technologies, such as shot peening, both in preventive manufacturing treatments and maintenance/repair operations [...]

Dynamic mission abort policy for systems operating in a controllable environment with self-healing mechanism

Catastrophic failures of safety-critical systems could result in significant economic losses and damage. To improve the survival probability of safety-critical systems, self-healing mechanism is usually considered in the design stage and mission abort may be conducted if the failure risk becomes too high. We investigate the optimal mission abort policies for systems subject to a controllable shock process with self-healing mechanism. Minor failure and catastrophic failures are two competing failure modes of the system. Imperfect repair is carried out when a minor failure occurs and the external shock process is renewed after the imperfect repair. Mission abort decisions are considered based on the time in mission and the number of experienced minor failures. The optimal mission abort problem is formulated within the framework of stochastic dynamic programming to minimize the expected total cost of mission failure, system failure and imperfect repair. The structural properties of the optimal policy are investigated using the optimal stopping theory and a case study is presented to illustrate the obtained results.

Reinforcement learning for dynamic condition-based maintenance of a system with individually repairable components

In this article, a reinforcement learning approach is used to develop a new dynamic maintenance policy for multi-component systems with individually repairable components, where each component experiences two competing failure processes of degradation and random shocks. The gamma process is used to model the degradation path of each component in the system. It is assumed that each incoming shock causes damage to the degradation path of all the components. A combination of component degradation is then used to define the system states. The optimal maintenance action for each component at each specific state is found by modeling the problem as Markov decision process and solving it by using a Q-learning algorithm. Using a reinforcement learning approach provides a more time-efficient and cost-effective method compared to the traditional maintenance optimization solutions, and it can also provide a dynamic maintenance policy for each specific degradation state of the system which is more useful and beneficial compared to the fixed or stationary maintenance plan which is often proposed by previous studies. A numerical example shows how the reinforcement learning can be used to find the optimal maintenance action for systems with different system configurations.

Experimental investigation of polyurea coated aluminum plates under strong hydrodynamic shocks

Polyurea has been used in armor applications for over a decade. Its ability to mitigate shock waves and survive after experiencing large deformations makes it suitable for structural protection purposes. One of the many uses of polyurea coatings is in maritime structures, in which polyurea is not only a mechanical armor but can also serve as chemical protector against corrosion due to its high resistance to environmentally aggressive conditions. To further implement such applications, one must understand the effect of polyurea coatings on the overall structural response to hydrodynamic shocks. An experimental investigation of high-pressure shock-loaded polyurea coated aluminum plates is presented. These experiments add to previous experiments that are described in detail in Rijensky and Rittel (2016) [1]. The present experiments reveal the effects of polyurea coating on the fluid structure interaction taking place between shocked water and aluminum plates. This interaction can be the result of numerous scenarios ranging from violent blasts in water to relatively milder loads like wave slamming. Emphasis is put on the selection of the coated side of the aluminum plate, considering those different interactions and their influence on the structure. The presented setup is also an interesting experimental physics case study as the deformation under shock process involves soft materials, fluid-structure interaction and conventional engineering materials deforming all together and affecting one another. Whereas weak shock mitigation was found to favor polyurea on the wet side of the plate, the present work reveals that for strong shocks, polyurea must now be applied on the dry side, thereby revealing a dependence of the optimal placement of the protective layer on the shock intensity.

Modeling the interdependency between natural degradation process and random shocks

In this paper, an interdependent structure between the natural degradation process and random shock process is proposed and incorporated into the competing failure model. Interdependent means that shocks are assumed to have an impact on the natural degradation process, additionally, the natural degradation process can also influence random shocks. Therefore, the interdependent structure includes two-fold: a) the impact of random shocks on the natural degradation process, represented by the cumulative damage adding up to the natural degradation process and expressed by a compound Poisson distribution, which is commonly used by other researchers; b) the influence of natural degradation process toward random shocks (both the magnitude and damage of shocks), reflected by the natural-degradation-state varying thresholds used for categorizing shocks into safety zone, damage zone and fatal zone according to their magnitudes, and the natural-degradation-state varying cumulative damage of shocks in damage zone, which are considered for the first time. A closed-form reliability function is derived under the linear natural-degradation-state varying thresholds. Two illustrative examples are presented to demonstrate this approach, and results show that the developed interdependent relationship model can obtain a more practical estimation of the reliability.

Mission abort and rescue for multistate systems operating under the Poisson process of shocks

The paper discusses mission abort and rescue strategies for multistate systems with different levels of performance. A system operates in a random environment modeled by the non-homogeneous Poisson process of shocks. With each shock, the state of a system stochastically deteriorates gradually moving to the state of a total failure. To prevent this event and to increase a system survival probability, a mission can be aborted and a rescue procedure can be activated. The number of experienced shocks is a decision parameter for the corresponding optimization problem that aims at maximizing the mission success probability subject to providing the desired level of survival probability. A detailed numerical example illustrates our findings.

Reliability analysis of systems considering clusters of dependent degrading components

A new system reliability model is developed for complex multi-component systems when each component experiences multiple failure processes, and component degradation paths are stochastically dependent. The components degrade in clusters that behave similarly. Gamma process models are used to model the stochastic processes of individual component deterioration. Degradation paths of different components are clustered into different classes corresponding to different operational conditions or stresses. In this new model, hard and soft failure processes for each component are dependent due to simultaneous shared exposure to a shock process, and furthermore, degradation paths among components are also considered to be probabilistically dependent. Degradation paths of components, not considering shock exposure, are often assumed to be independent, which is a common assumption, and it is often a realistic assumption. However, this new model is for the cases when pure degradation paths of different components are dependent in such a way that they can be classified into groups. One reason degradation paths could be dependent is because the components can be physically in contact or close to each other, and the degradation of one component impacts the other ones. Alternatively, random factors like temperature, wind speed, exposure to a polluted environment, etc., can affect degradation paths of all the components at the same time when components exist in a shared environment, causing another form of dependence. The new reliability model, considering stochastically dependent degradation paths among components, can be more realistic and practical for some applications. This is a new model when stochastically dependent component degradation paths are used in reliability models for systems subject to dependent competing failure processes.

Flow Modulation and Mixing Enhancement of Highly Underexpanded Jet by Vortex Excitation

A highly underexpanded jet with a nozzle pressure ratio of 5.60 is excited by a vortex excitation. Modulations on flow characteristics by the vortex excitation are revealed by comparing the excited jet with the free jet through a large-eddy simulation (LES) technique. The modeling results have achieved good agreements with the available literature data in terms of time-averaged near-field variables, Mach disk dimensions, and dominant frequencies. A grid-convergence study is also performed to verify the fidelity of LES results. Ultimately, qualitative and quantitative comparisons of mean and instantaneous jet fields are conducted. It is demonstrated that the vortex excitation has enhanced the mixing of the injection nitrogen with the environment by a considerably increased mixing level and a faster mixing process in the middle jet. The vortex excitation modulates the buildup process of shocks and vortex structures, resulting in an intensified shock/shear-layer interaction and an accelerated turbulence transition process, which combine to improve mixing efficiency. The dominant instability mode is altered to a higher-order multiple helical mode from a single helical mode, and an intensified screech tone is achieved by the vortex excitation.

Improving thermal shock and ablation resistance of high thermal conductivity carbon/carbon composites by introducing carbon nanotubes

In order to improve the thermal shock and ablation resistance of high thermal conductivity carbon/carbon composites, carbon nanotubes (CNTs) were introduced by electrophoretic deposition. After modification, the flexural strength of the composites increases by 53.0% due to the greatly strengthened interfaces. During thermal shock between 1100 °C and room temperature for 30 times, the strength continues to increase, attributed to the weakened interfaces in favor of fiber and CNT pull-out. By introducing CNTs at interfaces, thermal conductivity of the composites along the fiber axial direction decreases and that along the fiber radial direction increases. As the thermal shock process prolongs, since the carbon structure integrity of CNT and matrix in the modified composites is improved, the conductivity increases whatever the orientation is, until the thermal stress causes too many defects. As for the anti-ablation performance, the mass ablation rates of the CNT-modified composites with fibers parallel to and vertical to the flame decrease by 69.6% and 43.9% respectively, and the difference in the mass ablation rate related with fiber orientations becomes much less. Such performance improvement could be ascribed to the reduced oxidative damage and the enhanced interfaces.

Fatigue Property Test and Numerical Simulation Analysis of 2524 Aluminum Alloy by Laser Shock Process

Effects of laser shock peening on the fatigue properties of 2524 aluminum alloy were investigated by laser shock test, residual stress test and fatigue crack growth test respectively. The results show that the maximum residual stress is -220MPa at a distance of 1.1mm from the spot center after LSP (laser energy of 6.26J). The distribution of residual stress was simulated by Abaqus software, and the numerical simulation results were in good agreement with the experimental results. Compared with the untreated specimens, the fatigue life of the shocked specimens was increased by 32%. Fatigue fracture morphologies of the final rupture zone also show that more dimples of significantly larger depth and size occur. The fatigue life of 2524 aluminum alloy can be effectively extended by laser shock process (LSP).

A general multivariate new better than used (MNBU) distribution and its properties

In this paper, we develop a general multivariate new better than used (MNBU) distribution based on a multivariate common shock model. Assuming that the external shock process follows the generalized Polya process and a shock can destroy each component with some given probability, the multivariate survival distribution is obtained. The dependence structure of the multivariate distribution is analyzed. The properties on the dependence order and the multivariate ageing are also studied. Finally, as a special case, we consider the distribution of the minimum random variable and briefly discuss its properties.

Improving the adobe material properties by laser material processing

Many of the old heritage buildings and even many current buildings in the world are made of adobe, which is a sustainable, inexpensive, and environmentally friendly material. The adobe buildings react harmoniously against gravity or lateral forces, but structural fractures and sudden forces such as natural disasters or moisture leakage are the main causes of making them vulnerable, especially against earthquakes. Strengthening and reinforcement of adobe materials have long been discussed, and techniques such as adding materials to adobe or plastering adobe walls have been used to increase its resistance. Here, laser shock processing operation is exploited to analyze the extent of change in mechanical strength and moisture resistance of adobe material and ultimately to test its applicability to heritage buildings. The distance between the focal point of the laser beam and the surface of the adobe is optimized while an optimum value is also obtained for laser intensity. Laser radiation increases the compressive strength and flexural strength of the adobe by 348% and 12%, with respect to the raw material, whereas no significant difference is observed in the tensile strength. Nevertheless, the hydrophobicity of the samples increases by upper defocus and increasing the defocus, improves the soil adhesion, and escalates the homogeneity and integrity of the surface. Microstructural analysis such as SEM, EDAX and XRD of raw, and laser-treated adobe material confirm these improvements and overall render laser treatments an interesting, beneficial candidate among adobe reinforcement techniques.

Effect of multiple laser shock processing on nano-scale microstructure of an aluminum alloy

In this study, nano-scale microstructural evolution in 6061-T6 alloy after laser shock processing (LSP) was studied. 6061-T6 alloy plate was subjected to multiple LSP. The LSP treated area was characterized by X-ray diffraction and the microstructure of the samples was analyzed by transmission electron microscopy. Focused Ion Beam (FIB) tools were used to prepare TEM samples in precise areas. It was found that even though aluminum had high stacking fault energy, LSP yielded to formation of ultrafine grains and deformation faults such as dislocation cells, stacking faults. The stacking fault probability (PSF) was obtained in LSP-treated alloy using X-Ray diffraction. Deformation induced stacking faults lead to the peak position shifts, broadening and asymmetry of diffraction. XRD analysis and TEM observations revealed significant densities of stacking faults in LSP-treated 6061-T6 alloy. And mechanical properties of LSP-treated alloy were also determined to understand the hardening behavior with high concentration of structural defects.