In most cases, scratching of the surface of a polymeric glass elicits brittle behavior and industrial solutions like coating have been successfully used to improve the scratch resistance. The origin of the success of the coating technique is still of great research interest since one of the limitations of this technique is the risk of cracking and chipping. In terms of interfacial adhesion characterization, a wide variety of methods have been used to assess this property of material systems. Nevertheless, the adhesion of coatings still remains to be successfully determined in a test which can reproduce the damage undergone by the coated surface during its real lifetime. In this context, scratch test constitutes a good candidate. The present study deals with the scratching technique as an interfacial adhesion measurement in coated systems. Using a single-asperity scratching device allowing in-situ observation of the scratch, the fracture of a thin nano-composite coating deposited on its substrate was investigated under different conditions of temperature and scratching speed. Four types of fracture kinetics were observed depending on these two variables. One of these exhibits a stable blister growth at the same speed as the movement of the indenter over hundreds micrometers. This slow and extensive growth of a blister was obtained at 80 °C at a scratching speed of 10 μm/s. When the blister has reached a certain size, it propagates with the indenter without increasing further in size: it constitutes the steady state blister growth. A variational form of the energy balance of a blistering process is proposed, which permits to assess the adhesion of the system. Actually, the energy spent in the delamination process can be determined by following the delaminated area during the blistering process with regard to the scratching distance. The main difficulty is to estimate the energy dissipated in plastic flow. Different tests were conducted with various indenters: spheres with different radius and roughness. Thanks to this multi-criterion approach, it was possible to fit a unique value of the adhesion in the case of experimental stable blistering growths. The results are discussed with regard to reliability and probe characteristics.

The neck portion of the human femur is the most vulnerable region to attract stress-induced fractures. The loads of the human body act on the hip joint and on the greater trochanter region through abductor muscles. The bone is a natural composite and a good example of functionally graded material (FGM). This study considers a probabilistic finite element approach to assess the critical stresses in the femur under static loads. Material properties assigned to the bone model are linearly elastic, isotropic and orthotropic. Material characterization in terms of bone density is established by Computed Tomography (CT) data. The strength reliability and safety margin are obtained using relevant limit state function. Sensitivity analysis with respect to random parameters provides basis for a possible implant material characterization.

Since few years a 3D electric lines is developed. But new applications will be to expose this circuit to high variation of temperature and use them for electronic power. Circuits lines are made of tungsten and insulation in alumina. These materials have different behavior. That difference implies mechanics stress and stress singularities. Some stress concentration can fracture materials or interface between them. Alumina is a brittle material. We need to know his fracture behavior. A statistic model is already used: Weibull model. The idea is to break about hundred samples and to related the probabilities to break of alumina used in the circuit versus stress.

In this paper, we discuss a new way to model damage growth in solids. A level set is used to separate the undamaged zone from the damaged zone. In the damaged zone, the damage variable is an explicit function of the level set. This function is a parameter of the model. Beyond a critical length, it is assumed that the material is totally damaged, thus allowing a straightforward transition to fracture. The damage growth is expressed as a level set propagation. The configurational force driving the damage front is non local in the sense that it averages information over the thickness in the wake of the front. Three important theoretical advantages of the proposed approach are as follows: (a) The zone for which the materials is fully damaged is located inside a clearly identified domain (given by an iso-level set). (b) The non-locality steps in gradually in the model. At initiation the model is fully local. At initiation, micro-cracks being absent no length scale should prevail. (c) It is straightforward to prove that dissipation is positive. A numerical experiment of the cracking of a multiply perforated plate is discussed.

Quasi-static (∼10 −3 s −1 ) and high strain rate (∼850 s −1 ) compression behavior of an E-glass/polyester composite was determined in the through-thickness and in-plane directions. In both directions, modulus and failure strength increased with increasing strain rate. Higher strain rate sensitivity for both elastic modulus and failure strength was observed in the inplane direction. A numerical model was developed to investigate the compressive deformation and fracture of an E-glass/polyester composite. Excellent agreement was demonstrated for the case of high strain rate loading. Also, the fracture geometries were successfully predicted with the numerical model.

In this paper, the effect of three main parameters: a) welding speed, b) cooling rate of fluid flow through the main pipe; and c) number of welding passes, have been studied to obtain an effective method to reduce the burn-through risk during the in-service welding of AISI-316 pipe branch connection to perform hot-tapping. In addition, important patents regarding the new methods of hot-tapping have been reviewed. To carry out numerical simulation, a 3D Finite Element (FE) based thermo-mechanical model has been developed. Using this model, thermo-mechanical stresses and temperature distribution along the main-pipe wall-thickness have been obtained with maximum and minimum allowable welding speeds; and with two high and low level of steam flow rate through the main pipe. The Von-Mises yield criterion using the temperature dependent yield stress has been used to check the main pipe failure during the welding process. The results show that current techniques, including API recommendations, which only rely on the observation of the main-pipe inner wall temperature, does not take into account the effect of mechanical or thermal stresses due to the inline pressure or other working parameters which have significant role in burn-through. In addition, the results show that the increase of welding speed reduces the risk of burn-through but it increases the risk of hot cracking. On the other hand, decreasing the steam flow rate has the opposite effect. It has also been shown that using smaller electrode size is the most effective way to decrease burn-through risk.

Fine blanking is a near net shape process that is used for manufacturing of final product. In the fine blanking process, V-ring indentation is applied to create hydrostatic pressure and prevent premature fracture in an undesired direction. Furthermore, a small clearance between the punch and die is employed along with a counterforce punch that causes concentrated strain in the sheared band region. This process generally applies for sheet metal up to 6 mm. Application of this process for blanking of sheets thicker than 6 mm require some precautions for sound production. In the present research work, finite element analyses have been performed to investigate the effects of thickness variations on the shear band localization and shear surface quality in the fine blanking process. Simulations have been performed for two thicknesses of 6 and 8 mm. As blank materials, steel sheets of AISI 1045 have been used for numerical investigations.

The mechanical properties of magma around the glass transition temperature have not been characterized yet, though this subject is considered to be important in dynamics of volcanic eruptions. In this paper, we present an experimental investigation of stress-strain relation of synthetic magma at various temperatures and strain rates. The material behaves as an elastic solid at low temperature and/or high strain rate, and as a viscous fluid at high temperature and/or low strain rate. In the transition, it reveals work-hardening response. Although the work-hardening nature has not been reported for noncrystalline magma, it is important in constructing a mathematical model to represent the flow-to-fracture transition of magma, namely the transition of eruptions from effusive to explosive styles.

The procedure of limb lengthening is a common method for correcting limb length inequality. The lengthening procedure, however, can result in serious complications such as premature consolidation of bone and soft-tissue contractures. To avoid adverse effects, it is important to determine the safe limits of the lengthening procedure in terms of forces applied, rate of distraction, overall length added and effects of the procedure on associated tissue. In this study, we investigate the relationship between distraction speed and callus formation in the fracture gap and how this affects the distraction resisting force (DRF) and muscle adaptation. A new distraction system was designed to continuously measure the DRF during tibial lengthening using a unilateral fixator. Measurements were made in 2 sheep for 51 days and 38 days respectively. The first sheep acquired 5cm (25% of its original length) of new bone with various rates of distraction. The second sheep acquired 3.8cm (15% of its original length) of new bone with 1mm/day fixed rate of distraction. During the lengthening procedure, the DRF steadily increased as the callus was being formed in the distraction gap. In sheep1 the lengthening rate was increased from 1mm/day to 1.25mm/day at the lengthening day 36 to manage what was interpreted to be signs of early premature consolidation. The DRF decreased to 310N from 400N at the lengthening day 43. Radiographs taken at day 43 showed separation in the callus. During the 1.25mm/day lengthening the sheep lost ankle joint movement completely. The major muscles, long digital extensor (LDE), cranial tibial (CT), gastrocnemius and deep digital flexor (DDF) were collected from the operated and non-operated hind limbs. The result showed that LDE and CT were damaged while gastrocnemius and DDF were intact. In sheep2, the distraction rate was maintained at 1mm/day and it showed a similar increase of DRF up to 550N at the end of distraction (lengthening day 38). There was no visible joint restriction observed. None of the four muscles collected showed signs of the profound tissue damage noted in sheep1. Comparison of the DRF profile with radiological interpretation confirmed that the degree of callus formation was appropriate at DRF of 300 ∼ 500N. Additionally the ability of the muscle to adapt to the given length could be affected by the time when the rate was changed. Additional studies are underway to determine the optimal regimen including appropriate rates and forces.

The equivalent thermal load was previously shown to be the only feasible method by which the residual stresses due to autofrettage and its redistribution, as a result of cracking, can be implemented in a finite element analysis, of a fully or partially autofrettaged thick-walled cylindrical pressure vessel. The present analysis involves developing a similar methodology for treating an autofrettaged thick-walled spherical pressure vessel. A general procedure for evaluating the equivalent temperature loading for simulating an arbitrary, analytical or numerical, spherosymmetric autofrettage residual stress field in a spherical pressure vessel is developed. Once presented, the algorithm is applied to two distinct cases. In the first case, an analytical expression for the equivalent thermal loading is obtained for the ideal autofrettage stress field in a spherical shell. In the second case, the algorithm is applied to the discrete numerical values of a realistic autofrettage residual stress field incorporating the Bauschinger effect. As a result, a discrete equivalent temperature field is obtained. Furthermore, a finite element analysis is performed for each of the above cases, applying the respective temperature field to the spherical vessel. The induced stress fields are evaluated for each case and then compared to the original stress. The finite element results prove that the proposed procedure yields equivalent temperature fields that in turn simulate very accurately the residual stress fields for both the ideal and the realistic autofrettage cases.

Metabolic bone diseases are at the forefront of scientific and biomedical research worldwide. Diseases such as osteoporosis are characterized by increased bone fragility, which leads to micro-architectural deterioration of bone tissue and eventually to micro fractures. At the micro-structural level, bone is constructed from thin rods known as trabeculae and plates. These rods and plates are arranged in semi-regular, three-dimensional patterns and constitute highly anisotropic and heterogenic material. The bone micro-structure is stochastic in nature and varies according to patient, bone type and location within a specific bone. Diagnostic abilities rely on high technology and advanced methods for 3D micro scanning, modeling and analyzing the bone micro-structure. We propose a novel method for modeling scaffold-based implants that have the stochastic structure of bone and can be customized according to given bone structures. The method for designing these implants is based on a 3D pattern synthesis technique that can be applied to the diseased cavities of a given bone. The implants will replace these cavities in the cancellous bone. Recognizing these cavities is a difficult process, since such bone is characterized by a complex micro-structure composed of thin cylindrical rods and plates. Cavities with this 3D micro-structure will be identified by measuring the volumes of those cavities and comparing them to a specified threshold. The in-filling will be based on a 3D pattern growing scheme that takes the exerted forces into account so that the global directionality of the micro-structure is preserved. Furthermore, the goal is to optimize the topology according to mechanical rules. Due to the complexity of the problem, the approach is initially examined only for 2D medical images. The main contribution of this method is that the structure of the micro-implants will not be the current standard structure (cubes with holes), which lack the characteristics of a given bone structure. Moreover, this method can be used to design and manufacture customized micro-implants according to the specific stochastic micro-structure of a given bone. These customized designed implants can be manufactured using micro-RP technology.

Generally, most waterpower plants have to function under energy system peak load operation. Thus, there is a relatively quick water level variation observed in water-storage reservoirs, which contributes to the problems, especially in case of high-pressure waterworks facilities. Swift reservoir draw-down enhances seepage volumetric forces acting from the rock mass, which may lead to rock mass cracking and eventually to the development of landslide processes. A rapid impoundment of the water-storage reservoir is no less damaging. In this case, seepage in the rock mass is progressing in non-steady conditions, there occurring, in the inception stage: - high magnitude seepage hydrodynamic forces at the rock mass surface, creating additional loads on the rock mass, causing deflection of its surface, which may promote dam-foundation contact opening; - with increased pore pressures and seepage gradients, there may occur suffusion and other undesirable processes in the rock mass. In the work is given a numerical analysis of some parameters of seepage mode given based on right-bank investigation admitting presence of break in the dam filling-up mode. Options of time-intervals for the two basic versions – in case of sudden rising of water level in the upstream and in case of slow filling-up and setting up steady-state seepage mode in the massive – are being discussed. Determination of seepage flow parameters (including gradients) requires nonstationary field task to be solved. Finite-elements approximation for time analysis of the task is solved by finite-difference scheme. Seepage calculations are carried out by cyclic-iteration scheme – where volumetric water content, hydraulic conductivity and elasticity module determined numerically by functional relations. The subject of research is Enguri waterpower plant arch dam, at present the highest in the world (Georgia, height 271.5m, fig. 1.1). Consideration is being given to a variety of cases: - canyon slope in the zone of major geological fracture; - foundation in the central part of the dam.

Some spherical pressure vessels are manufactured by methods such as the Integrated Hydro-Bulge Forming (IHBF) method, where the sphere is composed of a series of double curved petals welded along their meridional lines. Such vessels are susceptible to multiple radial cracking along the welds. For fatigue life assessment and fracture endurance of such vessels one needs to evaluate the Stress Intensity Factors SIF distribution along the fronts of these cracks. However, to date, only two-dimensional SIFs for one through the thickness crack in a thin spherical shells is available. In the present paper, mode I SIF distributions for a wide range of lunular and crescentic cracks are evaluated. The 3-D analysis is performed, via the FE method employing singular elements along the crack front, for three sphere geometries with outer to inner radius ratios of η = R o /R i = 1.1, 1.7, and 2.0. SIFs are evaluated for arrays containing n = 1–20 cracks,; for a wide range of crack depth to wall thickness ratio, a/t, from 0.025 to 0.8; and for various ellipticities of the crack, i.e., the ratio of crack depth to semi crack length, a/c, from 0.2 to 1.5. The obtained results clearly indicate that the SIFs are considerably affected by the three-dimensionality of the problem and by the geometrical parameters: the geometry of the sphere – η, the number of cracks in the array – n, the depth of the crack – a/t, and its ellipticity – a/c.

The near-earth space environment is cluttered with man-made debris and naturally occurring meteoroids, which is a big menace to the safety of satellites and spacecrafts. This paper is addressed on the failure response of aluminum shields under hypervelocity impact of milligrame level flyer. A compacted electric gun is employed to accelerate a mylar flyer up to 10 km/s. Failure response of Ly12 aluminum shields with different thickness and layers impacted by mylar flyer with different velocities is under investigation. The spallation is observed in the rear free surface of 4 mm thick monolithic aluminum shield, and its fracture mechanism changes from plastic to brittle when loading pressure is above 13 GPa. A perforation with a diameter 8 mm in the impacted area of the 4mm thick Ly12 shield is observed after which is impacted by 0.1 mm thick mylar flyer 8mm in diameter with velocity 8.2 km/s. When three layers of shields are impacted, the debris clouds (DC) are observed in the first and the second spaces respectively during the impact process by high speed camera, and its leftover can be observed on the surface of the third plate. The shape of the first debris cloud head is a little flat, and its speed of lateral expansion is very slow, which is different from those impacted by spherical projectile, and its formation mechanics mainly attributes to multi-spallations based on the analysis of simulation.

A comparison between fine and conventional blanking is carried out in this paper. In the fine blanking process, V-ring indentation is applied to create hydrostatic pressure and prevent premature fracture in an undesired direction. Furthermore, a small clearance between the punch and die is employed along with a counterforce punch that causes concentrated strain in the sheared band region. A fracture mechanics oriented finite element procedure has been employed in this research work in order to obtain the fracture path. The fracture path is found according to the stress and strain histories which are calculated in each element. The numerical results have shown that the sheared edge quality in the blanking process is strongly influenced by the fracture path. In fine blanking, there are various parameters affecting the sheared edge quality and dimensional accuracy. The finite element calculation is carried out for an axisymmetric model. The commercial finite element code ABAQUS V6.2 is employed along with a controlling program that is written in Visual BASIC.

Fracture of restored teeth is a problem in restorative dentistry since it has been estimated that 92 percent of fractured teeth have been previously restored. In a restored tooth, the stresses that occur at the tooth-restoration interface during loading could become large enough to fracture the tooth and/or restoration. The tooth preparation process for a dental restoration is therefore a classical optimization problem: tooth reduction must be minimized to preserve tooth tissue whilst stress levels must be kept low to avoid fracture of the restored tooth. The objective of the present study was to propose alternative optimized designs for a second upper premolar cavity preparation by means of structural shape optimization based on the finite element method and biological adaptive growth. Restored tooth models using the optimized cavity shapes exhibited significant reduction of stresses along the tooth-restoration interface. In the best case, the maximum stress value was reduced by more than 50 percent.

Ball milling is a material processing method that allows near room temperature process of elements in powder and permits to synthesize materials with peculiar properties otherwise difficult or impossible to obtain. Due to the repeated fractures and cold welding of the reactants particles, solid solutions, amorphous alloys and equilibrium nanostructured materials can be obtained. Products coming from mechanosynthesis process can be advantageously applied as high performance structural and functional materials. Different milling devices can be utilized for the powder processing: planetary mill, attritor, horizontal ball mill, 1D and 3D vibrating machines. The wide differentiation in configuration of the mills obstacles the development of a unified model on powder transformation kinetics in the milling process and then most of processing procedures are still developed by using a trial and error method. The focus of this paper is on a horizontal fixed vial ball mill; in this configuration a high speed rotor launches several tumbling against the vial wall. During hits, a quantity of energy is released to the trapped powder and the solid state reactions are promoted. To characterize the powder transformation process, knowledge of the kinematics of the balls system must be inferred. For this purpose an experimental setup based on digital image acquisition was constructed and the movement of balls inside the vial was filmed. Particle trace analysis methodology permitted to obtain balls trajectories, velocity vector field and total hit frequency. The kinetic energy of the impacting balls inside the vial was quantified, so that the energy released to the powder in a milling experiment can be estimated.

Pressure vessels are common equipment in oil, gas and petrochemical industries. In a hot containing fluid vessel, excessive temperature gradient at junction of skirt to head (weld line), can cause unpredicted high thermal stresses; Thereby fracture of the vessel may occur as a result of cyclic operation. Providing a hot box (air pocket) in crotch space is a economical, applicable and easy mounted method in order to reduce the intensity of thermal stresses. Natural convection due to temperature difference between the wall of pocket, will absorb heat near the hot wall (head of the vessel) and release that near the cold wall (skirt of the vessel), then the skirt wall conducts heat to the earth as a fin. This conjugated heat transfer removes the temperature gradient boundary at welded junction. This phenomena will lead the temperature gradient on the weld line from a sudden to smooth behavior, thereby the skirt-head junction, that is a critical region, could be protected from excessive thermal stresses. In this paper the profit of hot box and conjugated heat transfer in cavity has been demonstrated experimentally. As a result it is shown that the conductive heat transfer through the skirt (which acts as a fin) ensures the continuation of natural convection in the box. Also the governing equations has been solved numerically and compared with experimental results.

The response to low velocity impact loadings, which may occur during manufacturing, service and maintenance, is a key factor in the design of composite material structures. Many techniques, ranging from the adoption of tough matrices/high-strain fibers to the introduction of through-thickness reinforcement, have been proposed to improve the damage response of composite laminates subject to impact. The insertion of transverse reinforcing threads by stitching, in particular, appears very promising to restrict damage growth and to improve post-impact performance of laminates. In order to develop general models capable of addressing the issues of damage tolerance and resistance, detailed understanding of the nature and extent of damage, identification of the dominant fracture modes and assessment of the effect of stitches on the damage development are essential. In this study instrumented drop-weight tests were carried out to examine and compare the damage response of stitched and unstitched cross-ply graphite/epoxy laminates subject to low-velocity impact. The progression of damage and its relationship with impact and absorbed energy were investigated by means of an extensive series of damage observations, conducted with various techniques (X-radiography, ultrasonics, optical microscopy, deply).

This work presents some of the results obtained from an extensive experimental test campaign performed at the Department of Mechanical Nuclear and Production Engineering (DIMNP) of Pisa University with the partnership of Avio Propulsione Aerospaziale S.p.A. This test campaign, that is still being performed, is concerned with the characterization of teeth damage in high performance gear transmissions, such as aeronautical ones, characterized by high levels of velocity and load. Damage detection and monitoring have been pursued during all the tests in order to achieve a better understanding of causes and evolution of teeth damage. Moreover, to investigate the effects of different parameters on teeth damage, tests with different load, velocity, teeth geometry, materials and surface finishing, have been performed. The surface conditions of the gear teeth have been investigated using in particular two different instruments: a computer-controlled stylus profilometer able to perform 3D investigations and a scanning electron microscope (SEM) recently provided by a software for surface reconstruction. Qualitative and quantitative changes in surface roughness have been detected. Besides the experimental activity, numerical analyses have been also started for finding theoretical criteria for surface damage prediction; some few obtained results are presented. Due to the vastness of the work performed, only a survey of the main results obtained till now is presented in the paper.