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This paper aims to describe a numerical approach to the fragmentation of kidney stones by direct impact.

The numerical approach consists of a Lagrangian finite element formulation with dynamic insertion of cohesive‐free surfaces. Cohesive free surfaces are governed by a damage constitutive model whereas the continuum part of the mesh remains linear elastic. The impact of the metallic probe of the medical device is modeled with a displacement control of the nodes inside the area of impact on the stone.

The results show the relation between the total energy transmitted during the impact with the damage and the fragmentation (number of fragments and number of microcrack clusters) of the kidney stone. The paper establishes the existence of both, an activation and saturation energy level, that delimit a range optimum working energy transmitted during the impact. In particular, the computations show that, for the calcium oxalate monohydrate stone, the maximum energy supplied by the medical device (Lithoclast) coincides with the saturation energy level.

In medical investigations, the experimentation is always restricted to the availability of patients or specimens. In the particular case of the elimination of renal calculi, the literature exhibits an extensive number of works reporting the practical experience of medical doctors. However, there is still a lack of information that might help to understand and to improve the comminution of kidney stones.

This paper is concerned with the calibration and validation of a finite‐element model of dry sliding wear in metals. The model is formulated within a Lagrangian framework capable of accounting for large plastic deformations and history‐dependent material behavior. We resort to continuous adaptive meshing as a means of eliminating deformation‐induced element distortion, and of resolving fine features of the wear process such as contact boundary layers. Particular attention is devoted to a generalization of Archard’s law in which the hardness of the soft material is allowed to be a function of temperature. This dependence of hardness on temperature provides a means of capturing the observed experimental transition between severe wear rates at low speeds to mild wear rates at high speeds. Other features of the numerical model include: surface evolution due to wear; finite‐deformation J₂ thermoplasticity; heat generation and diffusion in the bulk; non‐equilibrium heat‐transfer across the contact interface; and frictional contact. The model is validated against a conventional test configuration consisting of a brass pin rubbing against a rotating steel plate.

This paper aims to present an analysis of several 3 D texture parameters for the entire wear scars obtained in severe regime, on a four-ball tester. The aim of this analysis is to correlate the tribological parameter as wear scar diameter to texture parameters.

Tested lubricants were rapeseed oil, rapeseed oil additivated with 1% Wt nano TiO₂ and rapeseed oil additivated with 1%Wt nano ZnO. The severe regime was applied for 1400 rpm and for loads increasing in steps of 50 N, from 500 to 900 N. Several analyzed roughness parameters (height parameters and functional ones) could be related to the evolution of a wear parameter, the wear scar diameter. Comparing the values for neat rapeseed oil and additivated variants, the texture parameters allow for evaluating if the additives protect or not the worn surfaces.

Measurements pointed out two groups of roughness parameters: one that has an evolution depending on wear scar diameter (WSD) and load (Sa, St, functional parameters) and one including Ssk that has shown no dependence on load and WSD. Also, the functional parameters Spk and Svk follow in a similar manner the wear parameter, WSD, but Sk is the least dependent on load. For the highest load, amplitude parameters such as Sa and St are following the tendency of WSD. Each lubricant has its particular correlation between wear parameters and texture quality, expressed by the help of a set of roughness parameters.

Such studies help tribologists to rank lubricants based on a combined analysis with wear parameters and texture parameters.

The results allow for evaluating new formulated lubricants.

The study on the quality on worn surfaces introduces the original idea of analyzing the entire wear scar surface (approximated by an ellipse with the axes as those experimentally measured) by the help of a set of 3 D roughness parameters.

Shear-induced strain localization in granular materials has been a hot topic under intensive research during the last four decades. However, the micromechanical process and mechanisms underlying the initiation and development of shear bands are still not fully understood. The purpose of this paper is to eliminate this deficiency.

The paper carries out several two-dimensional distinct element method simulations to examine various global and local micromechanical quantities particular the energy dissipation and local stress and strain invariants with a special emphasis on the initiation and propagation of shear bands. Moreover, the effects of various influential variables including initial void ratio, confining stress, inter-particle friction coefficient, rolling resistance coefficient, specimen slenderness and strain rate on the pattern, scope and degree of shear bands are investigated.

Novel findings of the relationship between sliding and rolling dissipation band and shear band are achieved, indicating a plastic dissipation nature for the shear band. The high inter-particle sliding or rolling resistance, relative small initial void ratio, relative low confining stress and high strain rate facilitate the formation of shear band. In addition, the specimen slenderness affects the pattern of shear band.

In this paper, a comprehensive and deep investigation on shear band formation linked with localization of energy dissipation and strain invariants was presented. The new findings on particle scale during shear band formation helps to develop robust micromechanics-based constitutive models in the future.

The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures.

A two‐dimensional finite element model is developed with an actual Al₂O₃‐10 vol% ZrO₂ microstructure. A bilinear, time‐independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro‐void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models.

Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro‐void brings about the increase of crack density rate.

This paper is the first step for predicting the lifetime of ceramic implants. The social implications would appear in the next few years about health issues.

This proposed finite element method allows describing fracture and fatigue behaviours of alumina‐zirconia microstructures for hip prosthesis, provided that a microstructure image is available.

There is a fractal characteristic in most engineering surfaces. Effects of the surface fractal parameters D, G and the material parameter φ on the static friction coefficient are discussed. The predicted static friction coefficient increases with the increase of normal load. This coincides with the fact that static friction coefficient is very low under very small normal load condition. Second, a fractal transition model is proposed which takes into account the change of fractal dimension D. The load‐contact area relationship based on fractal transition model is not simply an exponential function, and the prediction correlates well with the experimental results. The predicted static friction coefficient based on fractal transition model first increases with the increase of load, and then decrease with the increase of load. The transition point is near D=1.5.

The behavior of joints has a significant effect on the stability of water conveyance tunnel. The purpose of this paper is to study the contact and friction at the joint of the tunneling segment lining and establish its contact friction model. At the same time, the stress and deformation characteristics at the joint of the segment under hydrostatic load are analyzed.

In this study, the contact and friction in a bolted joint are examined using shear testing. The feasibility of the proposed model is verified by a numerical simulation of tests and a theoretical analysis. Accordingly, the effect of joints on the lining is explored under internal hydrostatic loading.

The results show that the openings of tunnel segments in joints gradually expand from the positions of the inner and outer edges to the location of the bolt. Moreover, the stress concentration zone is formed at the bolt. Under hydraulic loading, the opening displacement at the joint increases as the water pressure increases; nevertheless, it does not exceed engineering requirements. When the water pressure of the tunnel lining joint reaches 0.5 MPa, the opening of the joint slowly increases. When the water pressure exceeds 0.7 MPa, the opening of the joint rapidly and significantly increases.

Contact and friction in a bolted joint were examined using shear testing. A cohesive zone model of bolted joints was proposed based on test results. The influence of joint behavior on the stability of water conveyance tunnel was studied.

This paper aims to investigate the effects of fragment impacts to shaped charge warheads in terms of shaped charge jet formation geometries and penetration performances.

In experimental process, a fragment was accelerated to a shaped charge warhead by means of a powder gun to a velocity more than 1,000 m/s, and this impact led to conical damage in the explosive of the warhead. Deformation on the warhead was visualized using X-ray technique to observe holes generated during fragment impact. Penetration test was performed against AISI 1040 steel plates with the damaged shaped charge warhead. Penetration performance of shaped charge jet, which deviated from the symmetry axis, was simulated by using SPEED software with 3-D Eulerian method to validate the numerical modelling method by comparing penetration test and simulation results of damaged warhead.

Simulation and test results showed good correlation for the warhead in terms of penetration depth and hole geometry at the impact surface of steel plates. In addition, the effects of the numbers and the geometries of fragment holes on shaped charge jet penetration performances were investigated with validated numerical methods. Simulation results showed that the increase in the number of fragment holes in the explosive of the warhead led to particulation of shaped charge jet that diminished penetration depth in the target plate. Additionally, simulation results also showed that the fragment hole geometry in the explosive after different fragment impact angles affected the amount of jet deviation from the symmetry axis as well as penetration depth in the target plate.

The results obtained from the current study revealed that fragment impact angle and different number of fragment impact reduced the penetration performance of shaped charge warhead by influencing the symmetry of shaped charge jet negatively.

The current study fulfils the need to investigate how fragment impact on the shaped charge warhead affect the formation symmetry of shaped charge jet as well as penetration performance by experimental and numerical methods. Penetration performance result of asymmetric jet is compared by experimental and numerical studies. A detailed methodology on numerically modelling of the effect of fragment impact angle and number of fragment impact on shaped charge jet performance is given in this study.

The purpose of this paper is to study the effects of the choice of database and data retrieval methods on the research performance of a number of selected Asian universities from 33 countries using two different indicators (publication volume and citation count) and three subject fields (energy, environment and materials) during the period 2005‐2009.

To determine the effect of the choice of database, Scopus and Web of Science databases were queried to retrieve the publications and citations of the top ten Asian universities in three subject fields. In ascertaining the effect of data retrieval methods, the authors proposed a new data retrieval method called Keyword‐based Data Retrieval (KDR), which uses relevant keywords identified by independent experts to retrieve publications and their citations of the top 30 Asian universities in the Environment field from the entire Scopus database. The results were then compared with those retrieved using the Conventional Data Retrieval (CDR) method.

The Asian university ranking order is strongly affected by the choice of database, indicator, and the data retrieval method used. The KDR method yields many more publications and citation counts than the CDR method, shows better understanding of the university ranking results, and retrieves publications and citations in source titles outside those classified by the database. Moreover the publications found by the KDR method have a multidisciplinary research focus.

The paper concludes that KDR is a more suitable methodology to retrieve data for measuring university research performance, particularly in an environment where universities are increasingly engaging in multidisciplinary research.

The purpose of this study is to evaluate the scientific performance of universities by extending the application of the h‐index from the individual to the institutional level. A ranking of the world's top universities based on their h‐index scores was produced. The geographic distribution of the highly ranked universities by continent and by country was also analysed.

This study uses bibliometric analysis to rank the universities. In order to calculate their h‐index the numbers of papers and citations in each university were gathered from Web of Science, including the Science Citation Index and Social Science Citation Index. Authority control dealing with variations in university names ensured the accuracy of each university's number of published journal papers and the subsequent statistics of their citations.

It was found that a high correlation exists between the h‐index ranking generated in this study and that produced by Shanghai Jiao Tong University. The results confirm the validity of the h‐index in the assessment of research performance at the university level.

The h‐index has been used to evaluate research performance at the institutional level in several recent studies; however these studies evaluated institutions' performance only in certain disciplines or in a single country. This paper measures the research performance of universities all over the world, and the applicability of the h‐index at the institutional level was validated by calculating the correlation between the ranking result of the h‐index and the ranking by the Shanghai Jiao Tong University.