Antonio Caballero and Jean‐Francois Molinari
This paper aims to describe a numerical approach to the fragmentation of kidney stones by direct impact.
Abstract
Purpose
This paper aims to describe a numerical approach to the fragmentation of kidney stones by direct impact.
Design/methodology/approach
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.
Findings
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.
Originality/value
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.
Details
Keywords
Nicholas Piaquadio, N. Eva Wu, Morteza Sarailoo and Qiu Qin
A time-varying parametric epidemiological model with 5-population groups (susceptible, mildly infected, severely infected, recovered, and deceased) is fitted to a set of COVID-19…
Abstract
A time-varying parametric epidemiological model with 5-population groups (susceptible, mildly infected, severely infected, recovered, and deceased) is fitted to a set of COVID-19 pandemic data. The underlying dynamic process of the model is associated with a population-centric Markov chain (PCMC) rather than a node-centric Markov chain (NCMC) to reduce the state space dimension. This allows simulation in the form of a closed queueing network, achieving linear complexity with respect to the total population without necessitating a mean-field approximation. A Markov decision problem (MDP) is formulated and solved for a simplified 5-population model with a linear set of transition rates. Together with the queueing network for the simulation of epidemics, this illustrates the potential to simultaneously design pharmaceutical and non-pharmaceutical intervention policies with both public health and economic considerations.
Details
Keywords
J.F. Molinari, M. Ortiz, R. Radovitzky and E.A. Repetto
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…
Abstract
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.
Details
Keywords
Lorena Deleanu, Traian Florian Ionescu, George Catalin Cristea, Cornel Camil Suciu and Constantin Georgescu
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Research limitations/implications
Such studies help tribologists to rank lubricants based on a combined analysis with wear parameters and texture parameters.
Practical implications
The results allow for evaluating new formulated lubricants.
Originality/value
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.
Details
Keywords
Mingjing Jiang and Wangcheng Zhang
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/value
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.
Details
Keywords
This study discusses the concepts of responsible tourism and creative tourism through regenerative tourism, which has sparked a debate, particularly in the post-pandemic world…
Abstract
This study discusses the concepts of responsible tourism and creative tourism through regenerative tourism, which has sparked a debate, particularly in the post-pandemic world, and reviews these concepts in terms of their similarities and differences in light of current literature. It is also aimed to develop a framework within the scope of sustainable development goals for regenerative destination development through responsible and creative tourism. Within this context, this study analyzes the potential of responsible and creative tourism for regenerative destination development.
Details
Keywords
Kyungmok Kim, Jean Geringer and Bernard Forest
The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures.
Abstract
Purpose
The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures.
Design/methodology/approach
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.
Findings
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.
Social implications
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.
Originality/value
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.
Details
Keywords
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…
Abstract
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.
Details
Keywords
Bingqi Li, Zhenyu Zhang, Xiaogang Wang and Xiaonan Liu
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/value
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.
Details
Keywords
Hakan Hafizoglu, Huseyin Emrah Konokman, Latif Kesemen and Ali Kursat Atay
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.
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Practical implications
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.
Originality/value
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.