The most cited articles published since 2009, extracted from Scopus
Volume 52, Issue 3, December 2009, Pages 183-194
Filippo Berto | Paolo Lazzarin
A large bulk of experimental data from static tests of sharp and blunt V-notches and from fatigue tests of welded joints are presented in an unified way by using the mean value of the Strain Energy Density (SED) over a given finite-size volume surrounding the highly stressed regions. When the notch is blunt, the control area assumes a crescent shape and R0 is its width as measured along the notch bisector line. In plane problems, when cracks or pointed V-notches are considered, the volume becomes a circle or a circular sector, respectively. The radius R0 depends on material fracture toughness, ultimate tensile strength and Poisson's ratio in the case of static loads; it depends on the fatigue strength ΔσA of the butt ground welded joints and the Notch Stress Intensity Factor (NSIF) range ΔK1 in the case of welded joints under high cycle fatigue loading (with ΔσA and ΔK1 valid for 5 × 106 cycles). Dealing with welded joints characterised by a plate thickness greater than 6 mm, the final synthesis based on SED summarises nine hundred data taken from the literature while a new synthesis from spot-welded joints under tension and shear loading, characterised by a limited thickness of the main plate, is presented here for the first time (more than two hundred data). Dealing with static tests, about one thousand experimental data as taken from the recent literature are involved in the synthesis. The strong variability of the non-dimensional radius R/R0, ranging from about zero to about 1000, makes the check of the approach based on the mean value of the SED severe. © 2009 Elsevier Ltd. All rights reserved.
Volume 51, Issue 1, February 2009, Pages 11-32
George C. Sih
Appropriate combination of size and time scale can accommodate a crack to creep a few nano meters in months or to propagate 10 km in a couple of seconds. The tip does not have a real mass so to speak of, but it can pack a high energy state by activating the surrounding matter. Decrease and increase of activated mass is presumed to occur before and after scale transition depending on the direction of arrow of material damage. The segmentation threshold for each scale range is postulated to depend on the product of the squared of the crack tip velocity over(a, ̇) 2 and activated mass density M as W = M ↓ ↑ over(a, ̇) ↓ ↑ 2 and D = M ↓ ↑ over(a, ̇) ↑ ↓ 2. The quantities W and D are referred to, respectively, as the direct-absorption and self-dissipation energy density. The activated mass densities M ↓ ↑ and M ↓ ↑ can increase or decrease in opposition to the crack tip velocity over(a, ̇) as indicated by the subscript/superscript notation. The compensating effects of over(a, ̇) 2 and M are implicit to the physical process of expansion and/or contraction often used in cosmo physics modeling. The activated mass density has the same interpretation when applied to the scale sensitive crack tip behavior. Multiscaling when segmented may consist of - pico, nano, micro and macro. The material damage process can thus be simulated figuratively speaking by crack growth entailing non-uniform global and local energy transfer. Material damage by fatigue crack growth is used to illustrate the size/time arrow of large → small and slow → fast as advocated, respectively, by the thermodynamics of cold → hot and order → disorder. This incidentally is opposite to the direction of arrow in cosmic evolution such that the events follow small → large and fast → slow while the thermodynamics reverses, respectively, to hot → cold and disorder → order. A new paradigm referred to as crack tip mechanics (CTM) is proposed to represent inhomogeneity by crack-like defects as the cause of damage initiation. The close ended line is depicted for simulating the interfacial gap between rows of atoms or a branch cut in a continuum. The range of the size time scale can cover from pico to macro or even wider range if necessary. Although the fatigue crack is used for demonstrating the basic principles of CTM, the scenarios of expansion and contraction associated with the direct-absorption and self-dissipation energy density in the context of cosmo physics can describe the behavior of the activated or energized mass around the crack tip which can be viewed as an energy sink or source. Singularity is used to capture the character of the energy source or sink, both physically as part of an interface or mathematically as part of a line of discontinuity. Energy exchange from one form to another is assumed to depend on the damage time of arrow of energy absorption or dissipation that involves the combine use of scale segmentation and singularity strength. Time degradation of the material constituents are derived according to specified design life such that the material response is matched with the time the history of the loading rate. A pico/nano/micro/macro fatigue cracking model of a 2024-T3 aluminum panel will be used for demonstration where the structure life portion may be added. Time degradation of the pico/nano/micro/macro/struc system behavior can be described by using nine scale transitional physical parameters: three for the nano/micro range (μ na / mi *,σ na / mi *, d na / mi *), three for the micro/macro range (μ mi / ma *, σ mi / ma *, d mi / ma *) and three for the pico/nano range (μ na / pi *, σ na / pi *, d na / pi *). The subscripts pi, na, mi, ma and struc designate, respectively, pico, nano, micro, macro and structure. Only the ratios of two successive scale sensitive parameters need to be known. The time dependent local physical parameters at the lower scale complete the formalism of analytical continuation though they need not be made known by tests. More specifically, the transitional character of picocracks, nanocracks, microcracks and macrocracks are determined from the specified life expectancy of time arrow according to pico → nano → micro → macro with the respective singularity strength of λ given by 1.25/1.00/0.75/0.50. An additional singularity of strength 0.25 may be added for the structural components. Recall that λ = 0.5 corresponds to the inverse square root r -0.5 in fracture mechanics with r being the distance from the macrocrack tip. The microcrack, nanocrack and picocrack tip are assigned with the singularities r -0.75, r -1.00 and r -1.25, respectively. The time of arrow in years will depend on the problem definition. A critical device component may be designed to operate at the pico/nano/micro/macro scale with a life distribution of 1.5 ±/2.5 ±/3.5 ±/5.5 ± and total life of 13 ± years. The superscript ± indicates more or less the actual time elapsed. Progressive damage is assumed to occur in the direction of pico → nano → micro → macro. The same scheme is applied to the fatigue damage of a 2024-T3 panel with a total life time of 20 years that may be distributed over the pico, nano, micro, macro and struc scale according to 1.5 ±/2.5 ±/3.5 ±/5.5 ±/7.0 ±. Such a specification can only be satisfied by matching the energy used in damaging the internal material structure at each scale range. Hence, the precise time dependent material property degradation process over the total life span can be enforced. © 2009 Elsevier Ltd. All rights reserved.
Volume 54, Issue 2, October 2010, Pages 82-90
Antonino Risitano | Giacomo Risitano
Following the first damage models proposed by Palmgren and Miner, numerous researchers have focused on the problem of predicting the residual life of a material from its load history. Every component dynamically loaded, particularly over the fatigue limit, shows an increase in temperature. The higher the temperature, the higher the load applied. Therefore, in an undamaged material or mechanical component, it is possible to associate each loading stress over the fatigue limit with a temperature value at the hottest point of the surface during the first phase of the test trough a thermo-mechanical characterization (TMC) map. Using the thermoanalysis of steel specimen data, this paper shows that the energetic effect (as a different temperature increments for equal loading uniaxial stress) can be used to evaluate the cumulative damage caused by previous loading. The tests were performed using C40 steel for which traditional fatigue curves in literature are reported. © 2010 Elsevier Ltd.
Volume 51, Issue 3, June 2009, Pages 149-160
George C. Sih
Validation of Ideomechanics (IDM) is manifested by removing the inconsistency of applying open system test data to closed system theories. Instead, the available open system test data can be used rightly to determine the physical parameters of the transitional functions defined by the mean values of length (free path), velocity, mass and energy. Multiscaling and size/time effects are considered. Ambiguities are mitigated when energy takes precedent in lieu of the concept of force. Determined directly from IDM is the energy density function from the velocity that can represent the magnitude of the energy sink and source. The formulation involves grouping pairs of variables of opposing poles that can be constructed as ideograms, much like yin-yang of I-Chin. The flow of Chi implicates the arrow of time and irreversibility. Mass activation/inactivation (AIA) is assumed to be related to the expansion/contraction (EXCO) of matter. Inadvertently, physical systems are identified with inhaling and exhaling of energy corresponding, respectively, to direct-absorption and self-dissipation (DASD). They are postulated to be the basic process for determining the integrity of the system. In contrast to Newtonian/Einsteinian mechanics (NEM) that uses field equations for determining the behavior of the whole everywhere for all time, IDM considers the mean behavior at any given size/time scale, however, large and small. Uncertainties are addressed by the scale transitional functions. The new paradigm can be applied to scaling shifting and to construct equivalence relations for open systems and to the use of existing test data free of ambiguities. Classical conservation laws for closed systems are reducible from the equivalence principles of open systems. The same holds for the classical kinetic molecular theory of matter that can be modified to include dissipation. © 2009 Elsevier Ltd. All rights reserved.
Volume 53, Issue 2, December 2010, Pages 94-112
George C. Sih
Multiscale material intends to enhance the strength and life of mechanical systems by matching the transmitted spatiotemporal energy distribution to the constituents at the different scale, say-macro, micro, nano, and pico,-, depending on the needs. Lower scale entities are, particularly, critical to small size systems. Large structures are less sensitive to microscopic effects. Scale shifting laws will be developed for relating test data from nano-, micro-, and macro-specimens. The benefit of reinforcement at the lower scale constituents needs to be justified at the macroscopic scale. Filling the void and space in regions of high energy density is considered. Material inhomogeneity interacts with specimen size. Their combined effect is non-equilibrium. Energy exchange between the environment and specimen becomes increasingly more significant as the specimen size is reduced. Perturbation of the operational conditions can further aggravate the situation. Scale transitional functions f j j+1 and/or f j/j+1 are introduced to quantify these characteristics. They are represented, respectively, by (f ma mi, f mi na, f na pi), and (f mi/ma, f na/mi, f pi/na) The abbreviations pi, na, mi, and ma refer to pico, nano, micro and macro. Local damage is assumed to initiate at a small scale, grows to a larger scale, and terminate at an even larger scale. The mechanism of energy absorption and dissipation will be introduced to develop a consistent book keeping system. Compaction of mass density for constituents of size 10 -12, 10 -9, 10 -6, 10 -3 m, will be considered. Energy dissipation at all scales must be accounted for. Dissipations at the smaller scale must not only be included but they must abide by the same physical and mathematical interpretation, in order to avoid inconsistencies when making connections with those at the larger scale where dissipations are eminent. Three fundamental Problems I, II, and III are stated. They correspond to the commonly used service conditions. Reference is made to a Representative Tip (RT), the location where energy absorption and dissipation takes place. The RT can be a crack tip or a particle. At the larger size scales, RT can refer to a region. Scale shifting of results from the very small to the very large is needed to identify the benefit of using multiscale materials. © 2010 Elsevier Ltd.
Volume 51, Issue 1, February 2009, Pages 33-40
Jim Lee | Xianqiao Wang | Youping Chen
Here we present a multiscale field theory for modeling and simulation of multi-grain material system which consists of several different kinds of single crystals and a large number of different kinds of discrete atoms. The theoretical construction of the multiscale field theory is briefly introduced. The interatomic forces are used to formulate the governing equations for the system. A compact tension specimen made of magnesium oxide is modeled by discrete atoms in front of the crack tip and finite elements in the far field. Results showing crack propagation through the atomic region are presented. © 2009 Elsevier Ltd. All rights reserved.
Volume 52, Issue 1, August 2009, Pages 14-21
Concrete is a material that is sensitive to the rate of loading. Understanding the dynamic behavior of concrete under various circumstances is an issue of great significance for applications in civilian and military engineering. Hence, an experimental investigation on the dynamic mechanical properties of the reactive powder concrete (RPC) was conducted using the split-Hopkinson pressure bar (SHPB). The specimens were made with different steel fibre volume fractions and the strain rate ranged from 101 s-1 to 103 s-1. The results show the obvious rate-dependent mechanical behavior exists for RPC. Moreover, the different of the characteristic of energy absorbed are compared. © 2009 Elsevier Ltd. All rights reserved.
Volume 53, Issue 3, June 2010, Pages 165-179
George C. Sih
Systems with parts that vary in size from pico to macro inclusive are vulnerable of being incapacitated when a single part fails owing to deterioration of material properties. The majority of system failure can be attributed to incompatibility of integrated parts that were designed individually for general purpose. Total reliability calls for all parts, small and large, to be compatible in life spans. Mass, when regarded as energized matter, can vary as a function of time. This, in retrospect, explains why non-equilibrium and non-homogeneity cannot be avoided for multiscale shifting laws. A consistent and scale invariant definition of energy dissipation gives rise to mass pulsation, a common mechanism that seems to be applicable to living and non-living organisms. Scale shifting laws are developed from the use of transitional functions R j j+1 that stand for the mass ratios related to absorption energies W j j+1 and dissipation energies D j j+1. The notations j and j+. 1 stand for two successive scales: pi-na, na-mi, and mi-ma. Hence, the mass ratios R pi na,R na mi, and R mi ma can be referred to as the transitional inhomogeneity coefficients. They make up the scale shifting laws W j j+1=R j j+1D j j+1. Connection of the accelerated test data at the different scales, say from pico to nano to micro to macro, can be made by application of the definition of a scale invariant energy density dissipation function. On physical grounds, the segmented non-equilibrium and non-homogeneous test data can be connected through a velocity dependent mass and energy relation. Energy and power efficiency are defined to explore the macroscopic experiences to those at the lower scales. The time evolution properties of the material can also be derived as a package to include the accelerated test data, a procedure normally referred to as validation. The separation of derive-first and test-later, can never be abridged without ambiguities. Hence, total reliability of a system with many parts is advocated by judiciously matching the nine primary variables consisting of the initial disorder sizes, the time rates, and increments of the absorbed and dissipated energy density. The nine controllable variables consisting of life span distribution, energy, and power efficiencies for the three scale ranges are of secondary consideration. © 2010 Elsevier Ltd.
Volume 53, Issue 1, February 2010, Pages 47-60
Raj Kumar Das | P. W. Cleary
Breakage of rocks or particulates plays a major role in various industries, such as mineral and ore processing. Many of the processes used for fracturing materials in these industries have the requirement to produce specified size and/or shape of the products. Numerical modelling can assist in understanding and predicting complex fracture processes, and can be used in designing the equipment and setting the process parameters to ensure desired product quality. In this paper, a mesh-free numerical method, called Smoothed Particle Hydrodynamics (SPH), is extended to predict impact fracture of rocks. SPH is a particle based Lagrangian method which is particularly suited to the analysis of fracture due to its capacity to model large deformation and track the free surfaces generated. A continuum damage model is used to predict the fracture of rocks. Evolution of damage is predicted using the strain history of each particle. Damage inhibits the transmission of tensile stress between particles, and once it reaches unity, the particle is unable to transmit tensile stress, resulting in a macro-crack. Connected macro-cracks lead to complete fragmentation. Firstly, an Unconfined Compressive Strength (UCS) test under uniaxial compression of a rock sample is modelled using SPH and compared against experiments to validate the capability of SPH for prediction of fracture in rocks. The SPH prediction matched the well-known experimentally observed diagonal fracture pattern. SPH is subsequently used to simulate brittle fracture of rocks during impact. Rock specimens of different shapes are examined to determine the effects of shape on both the fracture pattern and the energy dissipation during impact fracture. Rock shape is found to have considerable influence on the fracture process, fragment sizes, energy dissipation, and post-fracture motion of the fragments. © 2009 Elsevier Ltd. All rights reserved.
Volume 51, Issue 2, April 2009, Pages 129-138
Qihu Qian | Xiaoping Zhou | Haiqing Yang | Yongxing Zhang | Xin Li
By means of numerical simulation, the special phenomenon of zonal disintegration of surrounding rock mass around the diversion tunnels of Jinping II Hydropower Station is analyzed in this paper. In order to model the growth and coalescence of cracks within rock mass in Jinping II Hydropower Station, the weak-element is adopted. When cracks coalesce, failure of deep crack-weakened rock masses occurs and fractured zone is formed. The present result is different from the one obtained by the traditional elasto-plastic theory. The numerical results show that the slip-line zonal fracture is created within rock mass around the diversion tunnels in Jinping II Hydropower Station. Meanwhile, the magnitude and distributions of fractured zones are determined by numerical simulation. It is shown that the present results are in good agreement with the one observed by model tests. Through sensitivity analysis, the effects of stress condition, cohesion and the angle of internal friction on the phenomenon of zonal disintegration is determined. © 2009 Elsevier Ltd. All rights reserved.
Volume 51, Issue 2, April 2009, Pages 117-128
Reactive powder concrete (RPC), a composite that has been developed in recent years, is a special mixture that is cured to have a higher compressive strength than that of concrete (about 200 MPa). Adding a few steel fibers can markedly increase its mechanical properties, such as tensile and bending strength, impact resistance and toughness. Hence, RPC is highly promising for use in the containment structures of nuclear power plants and in the protection of military facilities. This study evaluates the resistance of ultra-high strength concrete targets by high-velocity impact experiments. Test variables include the impact velocity and the amount of steel fibers added. The experimental results reveal that RPC plates, because of their higher compressive strength, are more fragile than normal concrete (NC) plates. However, adding a small amount of steel fibers significantly improved the impact resistance of the target plates. Moreover, a numerical simulation based on the nonlinear finite element code LS-DYNA was performed. The results of the numerical simulation have a good agreement with the experimental data and can be used for further research. © 2009 Elsevier Ltd. All rights reserved.
Volume 56, Issue 3, December 2011, Pages 140-147
Yuhshiou Tai | Tungliang Chu | Hsuanteh Hu | Jhaoying Wu
Reinforced concrete is the principal material for military engineering and nuclear power plant containment. However, impacts and explosions could completely destroy such structures, causing tremendous casualties and property loss. Hence, this study conducts an analysis on the propagation law of a blast pressure wave and the dynamic response of reinforced concrete structures under explosive pressure wave effects. This study uses proper state material parameters and equations and then applies the nonlinear finite element analysis software LS-DYNA to conduct a numerical simulation of a free-field explosion model. After comparison with the computed results from empirical equations and validating the reliability of the numerical analysis model, the destruction and influencing factors on reinforced concrete slabs, under the effects of a blast pressure wave, are investigated. The results can serve as a reference for future analysis and design. © 2011 Elsevier Ltd.
Volume 51, Issue 2, April 2009, Pages 139-143
Chao Xie | Youwen Liu | Qihong Fang | M. Deng
This work is concerned with the cracking characteristics of mixed mode dislocations near a lip-like mode crack, stress intensity and strain energy density factor are obtained by using conformal mapping, singularity analysis and Cauchy integrals. Shielding effect generated by screw dislocation near a lip-like mode crack decreases with the increment of the distance between screw dislocation and crack tip. Larger distance between two faces of the crack leads to the shielding effect waning. The strain energy density factor of mode III decreases with the increment of the distance between dislocation and crack tip. Larger distance between two faces of lip-like mode crack also leads to the strain energy density factor waning and encourages crack initiation; the shielding effects generated by edge dislocation near the crack decrease with the increment of the distance between edge dislocation and crack tip. © 2009 Elsevier Ltd. All rights reserved.
Volume 52, Issue 2, October 2009, Pages 111-116
Zhiliang Wang | Heinz Konietzky | Ruiyuan Huang
This paper presents a numerical analysis of crater blasting in steel fiber reinforced concrete (SFRC). In order to model the nonlinear damage-softening behavior of SFRC, the effective stress and effective plastic strain curve is tabulated and used as input for the material Type10 (MAT_ELASTIC_PLASTIC_HYDRO) available in LS-DYNA. The Gruneisen equation of state (EOS) is used to model the pressure volume relationship. With the two erosion criteria namely tensile cut-off and failure strain incorporated, the crater blasting in SFRC is simulated. Numerical results show that the adopted model and high-pressure EOS can well capture the main characteristics and failure process of SFRC under blast loading, and the related parameters can be determined conveniently. In addition, the volume fraction of fibers exerts a significant influence on the dimension of blast-induced crater. © 2009 Elsevier Ltd. All rights reserved.
Volume 53, Issue 1, February 2010, Pages 1-8
Yuhshiou Tai | Meiyun Huang | Hsuanteh Hu
Non-linear finite element software LS-DYNA is used to analyze the axial compression behavior and energy absorption of a high-strength thin-walled member under an impact load. To elucidate the effect of dynamic impact on the strain rate, the Cowper-Symonds equation is applied to analyze the plastic state of stress and the onset of dynamic yielding under different strain rates, such that the modeled deformation behavior of the member is consistent with the actual situation. Results for the thin-walled members made of mild steel and dual phase steel are compared. Assuming two different materials with equal sectional areas, an analysis confirms that the energy absorption of high-strength steel thin-walled component is better than the mild steel thin-walled component. Hence, thin-walled tubes made of high-strength steel are investigated using a series of analysis. The relationships between displacement and load, average load and energy absorption properties are obtained. © 2009 Elsevier Ltd. All rights reserved.
Volume 52, Issue 3, December 2009, Pages 158-164
S. K. Georgantzinos | Georgios I. Giannopoulos | N. K. Anifantis
The excellent properties of carbon nanotubes have generated technological interests in the development of nanotube/rubber composites. This paper describes a finite element formulation that is appropriate for the numerical prediction of the mechanical behavior of rubber-like materials which are reinforced with single walled carbon nanotubes. The considered composite material consists of continuous aligned single walled carbon nanotubes which are uniformly distributed within the rubber material. It is assumed that the carbon nanotubes are imperfectly bonded with the matrix. Based on the micromechanical theory, the mechanical behavior of the composite may be predicted by utilizing a representative volume element. Within the representative volume element, the reinforcement is modeled according to its atomistic microstructure. Therefore, non-linear spring-based line elements are employed to simulate the discrete geometrical structure and behavior of the single-walled carbon nanotube. On the other hand, the matrix is modeled as a continuum medium by utilizing solid elements. In order to describe its behavior an appropriate constitutive material model is adopted. Finally, the interfacial region is simulated via the use of special joint elements of variable stiffness which interconnect the two materials in a discrete manner. Using the proposed multi-scale model, the stress-strain behavior for various values of reinforcement volume fraction and interfacial stiffness is extracted. The influence of the single walled carbon nanotube addition within the rubber is clearly illustrated and discussed. © 2009 Elsevier Ltd. All rights reserved.
Volume 56, Issue 3, December 2011, Pages 127-139
Reza Afshar | Filippo Berto
Stress concentration factors (SCFs) of a number of flat plates and round bars with periodic U- and V-notches are evaluated. Tension, bending and torsion loadings are considered in the investigation. The main objective of the investigation is to take advantage of the local strain energy density (SED) averaged on a control volume surrounding the tip of the middle notch and to estimate the SCF of each component by using a relatively coarse mesh. The unique advantage of SED method is the most prominent application of such a technique in the current study. Systematic FE simulations by considering a wide range of notch acuity and relative frequency of periodic U- and V-notch components are performed. More than two hundred and fifty models have been examined. The results of this study are compared with those provided by other researchers in the past and recent literature. Two new expressions of the notch depth reduction factor for the case of normal stresses (tension and bending) and torsion are also proposed to match the results from SED approach. © 2011 Elsevier Ltd.
Volume 53, Issue 2, March 2010, Pages 127-135
Filippo Berto | Paolo Lazzarin
The Fictitious Notch Rounding approach (FNR) is applied here for the first time to V-shaped notches under in-plane shear loading. The fictitious radius is evaluated for different opening angles as a function of the Microstructural Characteristic Length (MCL), the actual radius and the failure hypothesis. A multiaxiality factor is introduced and found to be very sensitive to the opening angle. Under mode II loading, the problem is more complex than under mode I and mode III, mainly because the maximum elastic stress is outside the notch bisector line. The main problem is the choice of the expected crack initiation angle, which defines the direction where the relevant stress has to be integrated. This integration carried out over the MCL gives the effective stress value for the pointed V-notch. To this end, two different criteria are used, the Maximum Tangential Stress (MTS) criterion and the Minimum Strain Energy Density criterion (MSED). A large number of finite element analyses have been carried out to determine the multiaxiality factor. This factor has been evaluated by comparing the theoretical stress concentration factor (SCF) obtained from fictitiously rounded notches to the effective stress concentration factor obtained by integrating the relevant stress over the Microstructural Characteristic Length. © 2010 Elsevier Ltd.
Volume 53, Issue 2, March 2010, Pages 89-93
Jan Klusák | Zdeněk Knésl
Joints of different materials have many applications in structural engineering and microelectronics. In the present contribution the joint is modelled as a bi-material notch. The singular stress field near the notch tip is investigated. Depending on the notch geometry and materials, the stress field can have one or two singularities. It is shown that to study the problem of a crack onset at the notch, both terms have to be taken into account. Criteria for the direction and for crack nucleation are formulated. The approach uti- lizes the knowledge of the strain energy density factor distribution in a bi-material notch vicinity. © 2010 Elsevier Ltd.
Volume 54, Issue 1, August 2010, Pages 63-70
Surajit Kumar Paul | S. Sivaprasad | Sankar Dhar | Soumitra Tarafder
Low cycle fatigue experiments have been conducted on 304LN stainless steel in ambient air at room temperature. Uniaxial ratcheting behavior has also been studied on this material and in both engineering and true stress controlling modes. It is shown that material's cyclic hardening/softening behavior in low cycle fatigue and in ratcheting is dependent not only on material but also on the loading condition. Improvement of ratcheting life and mean stress dependent hardening are observed in the presence of mean stress. A method based on the strain energy density (SED) is used to represent cyclic hardening/softening behavior of the material in this work. The decrease of SED with cycles is an indication that the life in low cycle fatigue and in ratcheting is improved. The SED represents the area of the hysteresis loops. © 2010 Elsevier Ltd.
Volume 53, Issue 3, June 2010, Pages 194-204
Bahattin Kilic | Erdogan Madenci
The peridynamic theory is advantageous for problems involving damage since the peridynamic equation of motion is valid everywhere, regardless of existing discontinuities, and an external criterion is not necessary for predicting damage initiation and propagation. However, the current solution methods for the equations of peridynamics utilize explicit time integration, which poses difficulties in simulations of most experiments under quasi-static conditions. Thus, there is a need to obtain steady-state solutions in order to validate peridynamic predictions against experimental measurements. This study presents an extension of dynamic relaxation methods for obtaining steady-state solutions of nonlinear peridynamic equations. © 2010 Elsevier Ltd.
Volume 52, Issue 1, August 2009, Pages 22-25
P. V. Yasnii | Pavlo O. Maruschak | Roman T. Bishchak | V. B. Hlado | Andriy P. Pylypenko
It was found that under the thermal cycle loading two interrelated process take place. In the material inner layers redistribution of dislocation and formation of sufficiently stable structure with the less dislocation density take place. Thus, the level of micro-stresses in the metal on the specimens surface and micro-hardness increases, which results in the elasticity exhaustion decrease of the metal micro-plastic deformation resistance. Localization of the micro-plastic deformations causes accumulation of the damage and initiation of microcracks. © 2009.
Volume 62, Issue 1, December 2012, Pages 26-33
Andrei Kotousov | Filippo Berto | Paolo Lazzarin | Fabio Pegorin
The 3D Finite Element method is applied to mixed fracture under anti-plane loading of a straight through-the-thickness crack in a linear elastic plate. This coupled fracture mode represents one of three-dimensional phenomena, which are currently largely ignored in numerical simulations and failure assessment of structural components weakened by cracks. It arises due to the boundary conditions on the plate free surfaces, which negate the transverse shear stress components corresponding to classical mode III. Instead, a new singular stress state in addition to the well-known 3D corner singularity is generated. This singular stress state (or coupled fracture mode) can affect or contribute significantly to the fracture initiation conditions. The coupled singular mode exists even if the applied anti-plane loading produces no singularities (KIII=0). In this case there is a strong thickness effect on the intensity of the coupled fracture mode. © 2013 Elsevier Ltd.
Volume 57, Issue 1, February 2012, Pages 49-54
Xiaoping Zhou | Guangqiang Chen | Qihu Qian
The zonal disintegration phenomenon is investigated for cross-anisotropic rock around a deep circular tunnel under hydrostatic pressure condition as well as the total elastic stress-field distributions. The number and size of fractured and non-fractured zones is determined by using the Mohr-Coulomb criterion. Effects of cross-anisotropic elastic parameters of deep rock mass on the zonal disintegration phenomenon are investigated. Numerical computations are carried out. It is shown from numerical results that the number and size of fractured and non-fractured zones significantly depend on to cross-anisotropic elastic parameters of deep rock mass. © 2011 Elsevier Ltd.
Volume 52, Issue 1, August 2009, Pages 40-49
Yinghao Hao Teo | Wingkong Chiu | Fukuo Chang | Nik Rajic
This paper discusses the scattering of stress waves by defects in representative aircraft structures with multi-layered construction and geometry variation. The approaches for determining and enhancing the probability of detection of non-surface-penetrating defects in such structures as well as minimising the contributions of multi-layered construction and geometry variation to false indications are presented. The results demonstrate the importance of selecting the appropriate frequency and location of the sensor in monitoring sub-surface defects on these structures. The findings suggested that a computer solution of the problem may be required to determine the optimal combination of frequency and sensor location. This study suggests the possibility of incorporating structural health monitoring into the design of future structures which will constitute a significant leap in the current knowledge base of structural health monitoring. © 2009 Elsevier Ltd.