Shell Fracture Research Articles

Phase-field analysis of finite-strain plates and shells including element subdivision

With the theme of fracture of finite-strain plates and shells based on a phase-field model of crack regularization, we introduce a new staggered algorithm for elastic and elasto-plastic materials. To account for correct fracture behavior in bending, two independent phase-fields are used, corresponding to the lower and upper faces of the shell. This is shown to provide a realistic behavior in bending-dominated problems, here illustrated in classical beam and plate problems. Finite strain behavior for both elastic and elasto-plastic constitutive laws is made compatible with the phase-field model by use of a consistent updated-Lagrangian algorithm. To guarantee sufficient resolution in the definition of the crack paths, a local remeshing algorithm based on the phase-field values at the lower and upper shell faces is introduced. In this local remeshing algorithm, two stages are used: edge-based element subdivision and node repositioning. Five representative numerical examples are shown, consisting of a bi-clamped beam, two versions of a square plate, the Keesecker pressurized cylinder problem, the Hexcan problem and the Muscat-Fenech and Atkins plate. All problems were successfully solved and the proposed solution was found to be robust and efficient.

Analytical Model on Stress-Regulated Lithiation Kinetics and Fracture of Si-C Yolk-Shell Anodes for Lithium-Ion Batteries

Despite various Si-based anode designs proposed by different researchers, the low areal capacity of these anodes remains an obstacle to their utilization as they still fail to meet the requirements for commercial Li-ion batteries. To tackle this challenge, a novel design of pomegranate-inspired Si-C yolk-shell composite anodes was developed recently, where single silicon nanoparticles are encapsulated by conductive carbon shells with void spaces between particles and shells to accommodate expansion. Despite overall excellent cycling performance, lithiation halting and carbon shell pulverization are experimentally observed in some Si-C yolk-shell anode designs, which undermine the structural integrity and limit the battery performance. Quantitative understanding of these failure modes is still lacking despite being critical to improve the yolk-shell anode designs. We present a theoretical study on lithiation-induced stress field in Si-C yolk-shell composite anodes and its influence on lithiation kinetics and mechanical degradation. For the first time, it is demonstrated that the contribution of surface stresses to the lithiation-induced stress field in nano-sized silicon anodes is negligible. We identify promising designs to achieve full anode capacity without carbon shell fracture while reducing consumption of carbon material. Results from the present study may offer insight on improving designs of Si-C yolk-shell composite anodes.

Outer organic layer and internal repair mechanism protects pteropod Limacina helicina from ocean acidification

Scarred shells of polar pteropod Limacina helicina collected from the Greenland Sea in June 2012 reveal a history of damage, most likely failed predation, in earlier life stages. Evidence of shell fracture and subsequent re-growth is commonly observed in specimens recovered from the sub-Arctic and further afield. However, at one site within sea–ice on the Greenland shelf, shells that had been subject to mechanical damage were also found to exhibit considerable dissolution. It was evident that shell dissolution was localised to areas where the organic, periostracal sheet that covers the outer shell had been damaged at some earlier stage during the animal’s life. Where the periostracum remained intact, the shell appeared pristine with no sign of dissolution. Specimens which appeared to be pristine following collection were incubated for four days. Scarring of shells that received periostracal damage during collection only became evident in specimens that were incubated in waters undersaturated with respect to aragonite, ΩAr≤1. While the waters from which the damaged specimens were collected at the Greenland Sea sea–ice margin were not ΩAr≤1, the water column did exhibit the lowest ΩAr values observed in the Greenland and Barents Seas, and was likely to have approached ΩAr≤1 during the winter months. We demonstrate that L. helicina shells are only susceptible to dissolution where both the periostracum has been breached and the aragonite beneath the breach is exposed to waters of ΩAr≤1. Exposure of multiple layers of aragonite in areas of deep dissolution indicate that, as with many molluscs, L. helicina is able to patch up dissolution damage to the shell by secreting additional aragonite internally and maintain their shell. We conclude that, unless breached, the periostracum provides an effective shield for pteropod shells against dissolution in waters ΩAr≤1, and when dissolution does occur the animal has an effective means of self-repair. We suggest that future studies of pteropod shell condition are undertaken on specimens from which the periostracum has not been removed in preparation.

Macroscopic approaches to the identification of expedient bivalve tools: A case study investigating Polymesoda (=Geloina) coaxans (Bivalvia: Corbiculidae) shell valves from Princess Charlotte Bay, Queensland, Australia

The identification of expedient bivalve tools recovered from archaeological deposits is currently hindered by a lack of analytical frameworks. In order to identify those shell valves which have been used as expedient tools, analysts must be able to identify and distinguish between pre-mortem and post-depositional modifications, and use-wear from tool use. Central to this difficulty is a lack of experimental analogues for comparison with archaeological material. Here, we present an analytical framework for the identification of expedient bivalve tools made from Polymesoda (=Geloina) coaxans valves recovered from Australian archaeological sites. This analytical framework consists of a series of actualistic experiments designed to determine those variables useful for distinguishing between modifications produced via pre-mortem and post-depositional processes that can damage molluscan shell, and damage produced via use as an expedient tool. Trampling, flaking and scraping experiments and use-wear analysis are used as a reference for comparison with an assemblage of P. coaxans valves recovered from archaeological sites in Princess Charlotte Bay, north Queensland, Australia. We demonstrate that an analytical framework consisting of an analysis of shell area loss, shell fracture paths, and use-wear can be successfully applied to archaeological samples to confidently distinguish between those valves which have been used as expedient tools, and those which have not. This research has wider implications for the identification of this often overlooked class of shell tools from archaeological sites in Australia and other regions, allowing a more comprehensive understanding of the place of shell tools in coastal economies of the past.

Organic egg production. II: The quality of organic eggs is influenced by hen genotype, diet and forage material analyzed by physical parameters, functional properties and sensory evaluation

The purpose of the study was to determine, how the dietary nutrients available in organic egg production, and especially how the obligatory forage material in relation to two different hen genotypes affects the quality of organic eggs evaluated by physical, functional and sensory properties. The experimental treatments were subjected to a total of 1200 hens, which were of two hen genotypes, representing a high egg yielding hybrid; Lohmann Silver (LS), and a dual-purpose hen genotype; New Hampshire (NH). They were fed three experimental feed diets (A, B and C), which were intended to differ in protein contents, hence methionine contents. Protein content of diets A, B and C were on average 203, 199, and 182g/kg dry matter, respectively, and methionine content were on average 3.9, 3.1, and 3.0g/kg dry matter, respectively. Furthermore, two forage material treatments were supplied (maize silage+carrots and alfalfa silage), altogether distributed in a complete randomized design with 4 replicate pens each of 25 hens. Each replicate pen had a separate house and outdoor hen yard of 4m2/hen. Eight times during the experimental period, from 22 to 41 weeks of age, eggs were collected for analysis of egg weight, egg dimensions, shell strength, egg yolk colour, carotenoid content of yolk, albumen pH, albumen DM, and albumen gel textural properties. Twice during the study, boiled eggs were evaluated for sensory properties. The results showed the hen genotype significantly influenced all analyzed egg quality parameters. Furthermore, the nutrient content of the diets significantly affected the egg weight and dimension, the shell fracture force, egg yolk colour, and carotenoid content. The forage material type also affected the egg quality. Feeding the alfalfa silage resulted in eggs of higher weight, no effect on shell quality, egg yolk colours of higher darkness, redness and yellowness, and a higher content of pigmenting carotenoids, but lower content of carotenes (α- and β-). No overall sensory differences of eggs from hens fed the two forage materials appeared, although some interaction effects were seen and are discussed.In conclusion, the egg quality in organic egg production is highly affected by the hen genotype, while further influence of the diet and forage material on the egg quality depends on the specific nutrients and compositions hereof.

Characterization of texture attributes of raw almond using a trained sensory panel

Introduction. Texture parameters are important factors for characterizing the sensory quality of raw almonds; nevertheless there is scarce literature that explores sensory differences among cultivars. The aim of this study was to characterize quality attributes of different raw almond cultivars. Materials and methods. The almond cultivars ‘Nonpareil’, ‘Mission’, ‘Supernova’, ‘Tuono’, ‘Ferragnes’ and ‘Marcona’ were used to characterize their industrial and sensory quality attributes. A panel of 14 assessors with previous experience in testing stone fruit was specifically trained on descriptive analysis for determining quality and particularly texture of raw almonds. Results and discussion. A direct relationship was observed between kernel yield and shell fracture resistance; the American cultivars ‘Nonpareil’, and ‘Mission’ showed more minor shell fracture resistance than the European. ‘Tuono’ stood out for being tasty, crunchy and hard, whereas ‘Marcona’ was noted for its color intensity, crispness and hardness; but it lacked taste. ‘Supernova’ was described as tasty. Conclusion. A 5-h training period proved to be adequate for characterizing raw almond cultivars. The panel was able to discriminate between cultivars and segregate ‘Nonpareil’ and ‘Mission’ from the other cultivars in terms of texture attributes.

Smoothed Particle Hydrodynamics for the Linear and Nonlinear Analyses of Elastoplastic Damage and Fracture of Shell

It is a troublesome and focused problem of solid mechanics to solve shell structures with Smoothed particle hydrodynamics (SPH), which is a fully meshfree method. In this paper, an integral model of SPH shell is proposed to more accurately capture the nonlinear strain along the thickness direction. Though the idea is similar to the "Gaussian integral point" in Finite element method (FEM), it is absent and just the first presentation in SPH. Furthermore, focusing on the metal materials, a high-efficiency iteration algorithm for plasticity is derived and the plastic damage theory of Lemaitre–Chaboche is also introduced based on the studies of Caleyron et al. (2011). As for the dynamic fracture of SPH shell, the multiple line segments algorithm is proposed to treat crack adaptively, which overcomes the mesh dependency occurring in mesh method. These algorithms and theories are successfully applied in the integral model of SPH shell of elasticity, plastic damage and dynamic fracture. Finally, the linear and nonlinear analyses of geometry and material are carried out with FEM, the global model and the integral model of SPH shell to prove the feasibility and the accuracy of the integral model.

Failure mechanisms in thin-walled nanocrystalline cylinders under uniaxial compression

Lattice materials composed of hollow nanocrystalline struts have recently made it possible to access new regions of material property space, by exploiting structural efficiencies along multiple length scales (nanometre to centimetre range). An important design issue for these materials is to understand how the failure mechanisms that act at these scales affect the macroscopic mechanical properties. In this study, we tested hollow nanocrystalline cylinders of two different grain sizes (20nm and 100nm) in uniaxial compression to investigate the effect of grain size on dominant failure mechanisms, and the influence of the latter on the compressive strength. The finite element method was used to model the interaction of the three observed failure mechanisms: shell buckling (SB), yielding (Y) and fracture (F). Depending on the grain size and geometry, the failure sequence can be SB–Y–F, Y–SB–F, SB–Y or Y–SB, the order of which has important implications in defining the limits of mechanical performance. One such implication is that when shell buckling occurs in the inelastic regime of the material, the macroscopic strength increase due to grain size refinement can be greater than the inherent yield strength increase of the material. Second, material fracture and shell buckling may not be competing failure mechanisms, which means that the effectiveness of grain size reduction in increasing the structural efficiency of cylindrical strut members can span the entire Hall–Petch range of the material.

Fracture of Cylindrical Shells Subjected to Internal Explosion: Numerical Simulation

Coupled analysis of explosion-driven fracture is a challenging task due to complicated fluid-structure interactions (FSI) and local large deformations. In this paper, a coupled Finite Element Method-Smoothed Particle Hydrodynamics (FEM-SPH) method was proposed to simulate the fracture of cylindrical shell subjected to internal explosion. The cylindrical shell was modeled by FEM and the movement of detonation products was modeled by SPH, where they were coupled by penalty contact algorithm. A rate-dependent failure criterion for steels at high strain rate conditions was employed in the simulation, which was presented and verified in our previous work. Results showed the interaction between blast wave and cylindrical shell, the dynamic crack propagation and the finial fracture morphology of cylindrical shell. The decoupled analysis was also conducted to make a comparison. It is found the coupled FEM-SPH method can well handle the complicated FSI problem which including local large deformations and ruptures. Compared with decoupled analysis, the fracture of coupled FEM-SPH analysis shows a better agreement with experimental results. In addition, though the over-predicted explosive loads in decoupled analysis cause a severer bulging deformation of cylindrical shell, but the finial fracture is smaller than that of coupled FEM-SPH analysis.

Simulation and Experiments of Hypervelocity Impact in Containers with Fluid and Granular Fillings

This paper presents both experiments and associated numerical simulations of hypervelocity impacts (approx. 3000m/s) of spherical aluminum projectiles onto hollow aluminum cylinders with either water or sand filling, which serve as representative filling substances for fluid and powdery materials, respectively. High-speed video technique is used to monitor the impact process. The paper mainly focuses on the following two subjects: (a) A direct comparison of failure and fracture of the container shell and the associated release of the filling depending on its type in both experiment and simulation. (b) With the above mentioned cases as reference examples, the applicability and efficiency of different numerical methods is investigated, such as Langrangian discretizations with Finite Element (FE)/Smoothed Particle Hydrodynamics (SPH) coupling, a coupled adaptive FE/SPH discretization and a coupled Euler/Lagrange method. The influence of the different simulation methods in terms of container failure representation and ejecta cloud properties is investigated and compared with the experimental results.

Disintegration of protein microbubbles in presence of acid and surfactants: a multi-step process.

The stability of protein microbubbles against addition of acid or surfactants was investigated. When these compounds were added, the microbubbles first released the encapsulated air. Subsequently, the protein shell completely disintegrated into nanometer-sized particles. The decrease in the number of intact microbubbles could be well described with the Weibull distribution. This distribution is based on two parameters, which suggests that two phenomena are responsible for the fracture of the microbubble shell. The microbubble shell is first weakened. Subsequently, the weakened protein shell fractures randomly. The probability of fracture turned out to be exponentially proportional to the concentration of acid and surfactant. A higher decay rate and a lower average breaking time were observed at higher acid or surfactant concentrations. For different surfactants, different decay rates were observed. The fact that the microbubble shell was ultimately disintegrated into nanometer-sized particles upon addition of acid or surfactants indicates that the interactions in the shell are non-covalent and most probably hydrophobic. After acid addition, the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay (release of air), while in the case of surfactant addition, there was a significant time gap between complete microbubble decay and complete shell disintegration.

TopClosure System Adapted to Chelonian Shell Repair

Chelonians suffering from traumatic shell fractures sustained from animal bites, car accidents, or rare accidents pertaining to illegal captivity (e.g., lawn mowers and electric shutters) are often seen at the Israeli Wildlife Hospital (IWH) in Ramat Gan, Israel. As shell fracture repair can be time consuming and difficult, often involving an extended healing period of a few months to >1 year, a successful repair process requires a reliable procedure that provides structural integrity. Veterinarians at the IWH have found that the TopClosure System (TCS) is a durable yet simple and inexpensive external fixation device that can easily be secured to fractured chelonian shells with dental acrylic adhesive. The TCS may be used noninvasively to stabilize shell fractures, while still enabling the use of conventional local treatment. The TCS repair technique was administered in the IWH for treatment of 7 chelonians: 3 Spur-thighed tortoises (Testudo graeca) and 4 Caspian turtles (Mauremys caspica), which were later released into their native environments. The TCS, a novel effective device originally designed for human soft tissue stretching, has successfully been used to mend chelonian shell fractures, while eliminating internal tissue damage and reducing any risk of infection.

Ductile Fracture of a Spherical Shell under Internal Pressure

Due to monotonically increasing internal pressure, a thick spherical shell of rigid plastic ductile material undergoes plastic deformation. Using Thomas's fracture theory, the critical pressure that causes fracture and the velocity as well as the stress during plastic flow, are estimated by analytical method.

Sulfur-TiO2 Yolk-Shell Nanoarchitecture for Long-Cycle Lithium-Sulfur Batteries

Sulfur is an attractive cathode material with a high specific capacity of 1,673 mAh g-1, but its rapid capacity decay due to polysulfide dissolution presents a significant technical challenge. Although much effort has been devoted to encapsulating sulfur particles with conducting materials to limit polysulfide dissolution, relatively little emphasis has been placed on dealing with the large volumetric expansion of the sulfur core during lithiation (~80%), which will lead to cracking and fracture of the protective shell. Here, we demonstrate the design of a sulfur–TiO2 yolk–shell nanoarchitecture with internal void space for stable and prolonged cycling over 1,000 charge/discharge cycles in lithium–sulfur batteries. Compared to bare sulfur and sulfur–TiO2 core–shell nanoparticles, the yolk–shell nanostructures were found to exhibit the highest capacity retention due to the presence of sufficient empty space to accommodate the volume expansion of sulfur, resulting in a structurally-intact TiO2 shell to minimize polysulfide dissolution. Using the yolk–shell nanoarchitecture, an initial specific capacity of 1,030 mAh g-1 at 0.5C and Coulombic efficiency of 98.4% over 1,000 cycles was achieved. Most importantly, the capacity decay after 1,000 cycles was found to be as small as 0.033% per cycle, which represents the one of the best performance for long-cycle lithium–sulfur batteries so far.

System approach to calculating processes in the apparatus of combined action

A method of calculating the apparatus of combined action for carrying out a high-temperature reaction in a fluidized bed of the solid reactant particles is proposed based on a system approach. In this bed, the reaction proceeds simultaneously with the continuous grinding of the formed products and the processes of heat and mass transfer are significantly intensified in connection with the constant renewal (denudation) of the reaction surface both due to the impact fracture of the product shell in the zones of the intensive collision in the counterflows of the reacting particles and its abrasion in the body of the fluidized bed.

Experimental and Numerical Investigations on the Dynamic Fracture of a Cylindrical Shell with Grooves Subjected to Internal Explosive Loading

AbstractA detailed experimental investigation on the dynamic fracture of a cylindrical shell with internal and external grooves subjected to internal explosive loading was carried out. Distributions of fragment velocities and fragment masses were measured and analyzed for specimens with different depths of the external grooves and different explosive materials, with the internal grooves of a fixed rectangular shape. Based on the experimental results, corresponding numerical simulations using the commercial software LS‐DYNA were undertaken. By inspecting the fragments recovered from the experiments and the numerical results, the dynamic fracture of the casing led to fragments of approximately three shapes: a large cuboid fragment, a small cuboid fragment, and two irregular fragments formed by three classical fracture trajectories. The formation mechanism of fragment shapes was analyzed using the fracture trajectories. A good agreement has been obtained between the numerical and experimental results. Finally, a parametric study for the casing thickness, grid patterns of the grooves and explosive materials was carried out in order to investigate the effects of fracture. The results showed that grid patterns of grooves and explosive materials had significant effects on the fracture mechanism of the casing. The numerical technique was used to predict the dynamic fracture of casing with internal and external grooves under internal explosive loading and for structural design in order to achieve desirable fragments with controlled shapes.

Microstructure and properties of SiCp/Al electronic packaging shell produced by liquid–solid separation

The electronic packaging shell of high silicon carbide (54%SiC, volume fraction) aluminum-based composites was produced by liquid–solid separation technique. The characteristics of distribution and morphology of SiC as well as the shell's fracture surface were examined by optical microscopy and scanning electron microscopy, and the thermo-physical and mechanical properties of the shell were also tested. The results show that Al matrix has a net-like structure while SiC is uniformly distributed in the Al matrix. The SiCp/Al composites have a low density of 2.93 g/cm3, and its relative density is 98.7%. Thermal conductivity of the composites is 175 W/(m·K), coefficient of thermal expansion (CTE) is 10.3×10−6 K−1 (25–400 °C), compressive strength is 496 MPa, bending strength is 404.5 MPa, and the main fracture mode is brittle fracture of SiC particles accompanied by ductile fracture of Al matrix. Its thermal conductivity is higher than that of Si/Al alloy, and its CTE matches with that of the chip material.

Creep and long-time fracture of a cylindrical shell under external pressure in the presence of an aggressive medium

We consider the process of deformation and fracture of an oval ring modeling the behavior of a long cylindrical shell subjected to distributed external pressure. The shell deformation is studied in both the presence and absence of an aggressive medium. The hypothesis of nonlinear viscosity with a singular component is taken for the constitutive relation used to estimate the metal characteristics. This relation allows for the difference between the tensile and compression strength of the material. The singularity permits taking into account not only the nonlinear viscosity but also instantaneous fracture characteristics. We show that an aggressive medium can substantially decrease the shell operation life.

Fracture and fragmentation of thin shells using the combined finite–discrete element method

SUMMARYA model for fracture and fragmentation of multilayered thin shells has been developed and implemented into the combined finite–discrete element code. The proposed model incorporates an extension of the original combined single and smeared fracture approach to multilayered thin shells; it then combines these with an interaction algorithm that is based on the original distributed potential contact force approach. The developed contact kinematics preserves both energy and momentum balance, whereas the developed fracture model is capable of modelling complex fracture patterns such as fracture of laminated glass under impact. Copyright © 2013 John Wiley & Sons, Ltd.

Long-term survival of the uncemented Balgrist total hip replacement cup

The purpose of this study was to evaluate the long-term clinical and radiographic outcomes of the Balgrist total hip replacement cup. We report the results of a retrospective review of 195 total hip prostheses with Balgrist cup implanted in 178 patients. There were 59 men and 119 women with a mean age at surgery of 52.3 years (range, 19-72). Cox regression was used to determine the influence of independent variables on the survivorship of the prosthesis. There were 117 (66 %) of 178 patients, and 131 (67 %) of 195 hips available for assessment at a mean follow-up of 17.4 years. A total of 21 patients (22 hips) were lost from follow-up (12 %). A total of 25 patients (27 hips) required some type of re-operation during the follow-up period. Eight of 27 re-operations (30 %) were directly caused by the Balgrist cup failure due to fatigue fracture of the metallic shell (n = 5; 19 %), polyethylene wear (n = 2; 7 %) and aseptic loosening (n = 1; 4 %). The mean polyethylene wear rate was 0.068 mm/year (range, 0.008-0.230; SD = 0.043). The risk of re-operation for any reason was decreased with dysplastic hip as a primary diagnosis (hazard ratio; HR = 0.250; 95 % CI 0.086-0.725) and with greater age at the time of surgery (HR = 0.923; 95 % CI 0.880-0.969). The 19-year survivorship with re-operation for any reason was 75.6 % (95 % CI 67.0-84.2). The 19-year survivorship with re-operation for the Balgrist cup failure was 90.5 % (95 % CI 83.4-97.6). The Balgrist cup continues to provide excellent clinical and radiological outcomes. This is associated at least in part with a low polyethylene wear rate. The main reason for the Balgrist cup failure is fatigue fracture of the metallic shell.