Multiple Impact Models Research Articles

Residual stress and crystallite size analysis of SMAT on AA7075-T6

The study examines how SMAT influences the microstructure, dislocation density, and residual stress of AA7075-T6 alloy. SMAT involves the repeated impact of shots on a material surface within a vibration chamber, inducing severe plastic deformation and grain refinement. The study explores the interplay between vibration-induced shot effects and their impact on surface properties, emphasizing the importance of optimizing process parameters for improved material performance. Experimental analyses, including surface and subsurface microstructure examinations, X-ray diffraction (XRD) characterization, and residual stress evaluations, are conducted to elucidate the underlying mechanisms of SMAT. Results indicate that SMAT leads to significant plastic deformation, grain size reduction, increased dislocation density, and microstrain. The treatment produces a nanocrystallite layer, enhancing material properties. Residual stress measurements reveal a surface stress of −245 MPa, increasing to −360 MPa at 50 µm depth. The proposed multiple impact model accurately predicts deformation behavior, highlighting the deep pit regions formed during SMAT. This comprehensive investigation provides insights into the dynamic nature of SMAT and its potential for enhancing material properties. By integrating experimental findings with numerical modeling approaches, the study advances our understanding of SMAT-induced plastic deformation mechanisms and residual stress profiles.

Numerical study of the simultaneous multiple impact phenomenon on CFRP plates

Composite laminates are currently used in various fields of engineering, in which they can be subjected to multiple impacts, reducing their service life. Typical examples of these phenomena are found in the high-speed rail industry. Several works have focused on this topic, but very few have exposed a methodology that verifies the existence of stress wave interaction, produced by the action of several projectiles that impact on a structure simultaneously. Therefore, this work aims to study the multiple impact response of composite laminates, as well as the influence of stress waves on their mechanical behaviour. For this purpose, a numerical multiple impact model was developed. This numerical model was validated with single impact experimental results taken from the literature. It was observed that the presence of more than one projectile in the impact event reduced the ballistic limit of composite laminate. Finally, it was concluded that stress waves influenced the impact response of CFRP plates.

A novel multiple impact model for predicting the residual stress state

Developing ultrahigh-strength structural materials that are ductile, fracture resistant, and cost effective has been a long-standing desire for scientists and engineers. Surface nano-crystallization technology has recently been developed as one of the most effective methods to optimize surface structure, which can improve local and global mechanical behavior without compromising ductility. This technique involves the use of hundreds of small hard balls vibrated by high-power ultrasound so that they impact onto the surface of a material at high speed, also known as surface mechanical abrasion treatment (SMAT). Despite its success in enhancing the mechanical properties of steels and other structural materials, there is still lack of clear understanding of the relationships between desired surface structures/properties and controlling parameters in such surface treatment processes. Therefore, we calculated residual stress through computational modeling such as finite element analysis (FEA), and simulated the effect of all parameters during processing on residual compressive stress. Different multiple impact models are investigated to develop a more realistic model for the strengthening process.

Residual stress prediction in shot blasted cobalt–chromium biomedical cast components

ASTM F75 implants distort due to residual stress released after finishing machining operations, causing implants to fail quality requirements. Previous work has shown that a shot blasting cleaning process could be the source of this distortion. Finite element analysis (FEA) is conducted to predict stress and Almen strip arc heights for experimental comparison. 2D and 3D single impact models and 3D multiple impact models are created. 3D multiple impact models with plastically deforming shot are shown to accurately predict the stress state and distortion. For shot with hardness similar to the implants, distortion creating stress magnitudes are induced, with the greatest fluctuations in stress coming from shot velocity. The depth of the predicted compressive stress layer ranges from 0.23 to 0.6 mm.

A Novel Multiple Impact Model for Predicting the Residual Stress State

A Novel Multiple Impact Model for Predicting the Residual Stress State

Strengthening Steels by Inducing Residual Stresses Via Mechanical Attrition

Making stronger and tougher structural steels has long been a desire for scientists and engineers. In particular, nano-crystallization techniques have been recently been developed as one of the most effective ways to optimize surface structure and therefore develop the local and global mechanical behavior in such a way as to increase strength without compromising ductility. In this paper, we present a computational analysis on a popular surface nano-crystallization technology that involves the use of hundreds of small hard balls which are vibrated using high-power ultrasound so that they impact onto the surface of a material at high speed. We focus specifically on the generation of beneficial residual stress in improving the damage-tolerant properties of an austenitic stainless steel as the target material. Different multiple impact models are investigated to develop a more realistic model for the strengtening process.

Modeling the Evolution of Residual Stresses in Thermally Sprayed YSZ Coating on Stainless Steel Substrate

This study is based on Eulerian method to model residual stresses for yttrium-stabilized zirconia coating applied to stainless steel substrate. A commercially available finite element software ABAQUS/Explicit is used to conduct this study. Single and multiple-particle impact analyses were carried out, and the residual stress data have been reported. The analysis is performed for two different values of thermal contact resistance and the through-thickness residual stress profiles obtained within the coating for single particle are tensile, while the substrate has a mixture of tensile and compressive residual stresses. For multiple impact model, the residual stress data have been presented for substrate with and without cooling. The residual stresses within the coating without substrate cooling are mostly tensile while the substrate is compressive. The residual stresses within the coating with substrate cooling are mostly tensile with compressive stresses on the top of the coating, while the substrate consists of compressive stresses. The obtained residual stresses are compared with experimental and analytical data.

Sources of uncertainty in hydrological climate impact assessment: a cross-scale study

Climate change impacts on water availability and hydrological extremes are major concerns as regards the Sustainable Development Goals. Impacts on hydrology are normally investigated as part of a modelling chain, in which climate projections from multiple climate models are used as inputs to multiple impact models, under different greenhouse gas emissions scenarios, which result in different amounts of global temperature rise. While the goal is generally to investigate the relevance of changes in climate for the water cycle, water resources or hydrological extremes, it is often the case that variations in other components of the model chain obscure the effect of climate scenario variation. This is particularly important when assessing the impacts of relatively lower magnitudes of global warming, such as those associated with the aspirational goals of the Paris Agreement.In our study, we use ANOVA (analyses of variance) to allocate and quantify the main sources of uncertainty in the hydrological impact modelling chain. In turn we determine the statistical significance of different sources of uncertainty. We achieve this by using a set of five climate models and up to 13 hydrological models, for nine large scale river basins across the globe, under four emissions scenarios. The impact variable we consider in our analysis is daily river discharge. We analyze overall water availability and flow regime, including seasonality, high flows and low flows. Scaling effects are investigated by separately looking at discharge generated by global and regional hydrological models respectively. Finally, we compare our results with other recently published studies.We find that small differences in global temperature rise associated with some emissions scenarios have mostly significant impacts on river discharge—however, climate model related uncertainty is so large that it obscures the sensitivity of the hydrological system.

Inter-model comparison of hydrological impacts of climate change on the Upper Blue Nile basin using ensemble of hydrological models and global climate models

The aim of this study was to investigate the impacts of future climate change on discharge and evapotranspiration of the Upper Blue Nile (UBN) basin using multiple global circulation models (GCMs) projections and multiple hydrological models (HMs). The uncertainties of projections originating from HMs, GCMs, and representative concentration pathways (RCPs) were also analyzed. This study is part of the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) initiative (phase 2), which is a community driven modeling effort to assess global socio-economic impacts of climate change. The baseline period of 1981–2010 was used to identify climate change signals in two future periods: mid future (2036–2065) and far future (2070–2099). Our analyses showed that two out of four GCMs indicated a statistically significant increase in projected precipitation in the far future period. The projected change in mean annual precipitation varied between 4 and 10% relative to the baseline period. The HMs did not agree on the direction of climate change impacts on mean annual discharge. Furthermore, simulated changes in mean annual discharge by all HMs, except SWIM which simulated up to 6.6% increase for the far future period, were not statistically significant. All the HMs generally simulated a statistically significant increase in annual mean actual evapotranspiration (AET) in both periods. The HMs simulated changes in AET ranging from 1.9 to 4.4% for the far future period. In the UBN basin GCM structure was the main contributor of uncertainty in mean annual discharge projection followed by HM structure and RCPs, respectively. The results from this research suggest to use multiple impact models as well as multiple GCMs to provide a more robust assessment of climate change impacts in the UBN basin.

Shock dynamics in granular chains: numerical simulations and comparison with experimental tests

The aim of this paper is to simulate the nonlinear wave propagation in granular chains of beads using a recently introduced multiple impact model and to compare numerical results to experimental ones. Different kinds of granular chains are investigated: monodisperse chains, tapered chains and stepped chains. Particular attention is paid to the dispersion effect, and the wave propagation in tapered chains, the interaction of two solitary waves in monodisperse chains, and the formation of solitary wave trains in stepped chains. We show that the main features of the wave propagation observed experimentally in these granular chains are very well reproduced. This proves that the considered multiple impact model and numerical scheme are able to encapsulate the main physical effects that occur in such multibody systems.

Multimodel Estimate of the Global Terrestrial Water Balance: Setup and First Results

AbstractSix land surface models and five global hydrological models participate in a model intercomparison project [Water Model Intercomparison Project (WaterMIP)], which for the first time compares simulation results of these different classes of models in a consistent way. In this paper, the simulation setup is described and aspects of the multimodel global terrestrial water balance are presented. All models were run at 0.5° spatial resolution for the global land areas for a 15-yr period (1985–99) using a newly developed global meteorological dataset. Simulated global terrestrial evapotranspiration, excluding Greenland and Antarctica, ranges from 415 to 586 mm yr−1 (from 60 000 to 85 000 km3 yr−1), and simulated runoff ranges from 290 to 457 mm yr−1 (from 42 000 to 66 000 km3 yr−1). Both the mean and median runoff fractions for the land surface models are lower than those of the global hydrological models, although the range is wider. Significant simulation differences between land surface and global hydrological models are found to be caused by the snow scheme employed. The physically based energy balance approach used by land surface models generally results in lower snow water equivalent values than the conceptual degree-day approach used by global hydrological models. Some differences in simulated runoff and evapotranspiration are explained by model parameterizations, although the processes included and parameterizations used are not distinct to either land surface models or global hydrological models. The results show that differences between models are a major source of uncertainty. Climate change impact studies thus need to use not only multiple climate models but also some other measure of uncertainty (e.g., multiple impact models).

다중 충돌의 영향을 고려한 쇼트피닝의 유한요소해석

Multiple impact models to examine the effect of stress intcrlercncc arc proposed alld illvcstigated. The single shot model analysis, which used various shot ball conditions. was carricd oul to compare with multiple impacts analysis. Then the multiplc impact analysis were performed to predict the crlect of the shot ball distances. The results showed that the stress interference in the multiple impact model significantly reduced the maximum value of the compressive residual stresses. The rcsidual strcss protiJes were strongly effected by the shot ball distances. The Illultiple impact model can simulatc a realistic shot peening process rather than a single shot model does. It is concluded that the proposed Illodel predicts the real process more accurately.<br/>

Studies of multiple ionization in the RF spark and vacuum vibrator arc ion sources

Relative abundance distributions of multiply-charged ionic species have been measured for the RF spark and vacuum vibrator are ion sources, for a number of elements. An attempt has been made to explain the observed charge state distribution on the basis of models for the arc and spark plasma. The difficulties in the way of explaining the observed charge state distributions, using the LTE model with Saha distribution as well as the corona model, are pointed out. The distribution can be explained by a diffusion-dominated plasma model with known or calculated values for ionization cross-sections, the single impact model being suitable for the RF spark and the multiple impact model for the vibrator arc.