Shell Fracture Research Articles

Investigation on dynamic response of thin spherical shells impacted by flat-nose projectile based on a novel damage model

Thin-shell structures are widely used in various engineering applications. It is essential to investigate the impact resistance of thin-shell structures, to provide theoretical support for engineering applications. Numerous impact tests have been conducted on thin spherical shells using ballistic guns. The effects of the impact velocity and shell thickness on the deformation and fracture of thin spherical shells are summarized. Moreover, a novel damage model based on statistic damage mechanics is proposed to better predict dynamic responses of thin shells impacted by projectiles. Considering that fracture surfaces are formed by void evolution and are affected by the stress states, the damage level is defined as the ratio of the statistical cross-sectional area of the voids to the cross-sectional area of the representative elements. Utilizing statistical methods, the incorporation of continuous void nucleation, ellipsoidal void growth, and the acceleration of dynamic void evolution are introduced into the novel damage model. Subsequently, numerical investigations of the dynamic response of spherical shells under impact are conducted based on the proposed damage model. The numerical results are consistent with the experimental results in terms of the depression deformations and strain signals. The effects of shell thickness and double-layer structures on the dynamic response of spherical shells are investigated via numerical simulations considering the novel damage model in detail. The results demonstrate that the proposed model can accurately predict the dynamic response of spherical shells impacted by flat-nose projectiles, thus serving as a valuable reference for engineering design.

Study on fracture of hyperelastic Kirchhoff-Love plates and shells by phase field method

Thin walled structures such as plates and shells are widely used in many engineering fields. To Predict its fracture behavior is of great significance for integrity design and strength evaluation of engineering structures. Numerical simulation of the fracture behavior of hyperelastic plates and shells is a challenge due to complex kinematic description, hyperelastic constitutive relationship, geometric nonlinearity and the degradation on elastic parameter caused by fracture damage. Combining Kirchhoff Love (K-L) shell theory with the fracture phase field method, and numerically discretizing the first and second order partial derivatives of displacement field and phase field by using T-splines and meeting the requirements of K-L plate and shell theory for the C1 continuity of the shape function, a model for the isogeometric analysis numerical formulation of the phase field fracture in hyperelastic K-L plates and shells is established. The fracture failure behavior of hyperelastic K-L plates and shells under the uniform load and displacement load is simulated, and the effect of the Gaussian curvature on the fracture behavior of hyperelastic K-L shells is studied. The simulation results show that the present numerical scheme can effectively capture the complex crack propagation path of plates and shells under the uniform load, and the displacement field can effectively reflect the crack distribution of materials. The thin shell with negative Gaussian curvature shows the excellent fracture performance under the internal pressure, and can withstand the greater internal pressure.

Crack propagation and damage evolution of metallic cylindrical shells under internal explosive loading

This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading. The calibration of four typical failure parameters for 40CrMnSiB steel was conducted through experiments and subsequently applied to simulations. The numerical simulation results employing the four failure criteria were compared with the differences and similarities observed in freeze-recovery tests and ultra-high-speed tests. This analysis addressed the critical issue of determining failure criteria for the fracture of a metal shell under internal explosive loads. Building upon this foundation, the damage parameter Dc, linked to the cumulative crack density, was defined based on the evolution characteristics of a substantial number of cracks. The relationship between the damage parameter and crack velocity over time was established, and the influence of the internal central pressure on the damage parameter and crack velocity was investigated. Variations in the fracture modes were found under different failure criteria, with the principal strain failure criterion proving to be the most effective for simulating 3D crack propagation in a pure shear fracture mode. Through statistical analysis of the shell penetration fracture radius data, it was determined that the fracture radius remained essentially constant during the crack evolution process and could be considered a constant. The propagation velocity of axial cracks ranged between 5300 m/s and 12600 m/s, surpassing the Rayleigh wave velocity of the shell material and decreasing linearly with time. The increase in shell damage exhibited an initial rapid phase, followed by deceleration, demonstrating accelerated damage during the propagation stage of the blast wave and decelerated damage after the arrival of the rarefaction wave. This study provides an effective approach for investigating crack propagation and damage evolution. The derived crack propagation and damage evolution law serves as a valuable reference for the development of crack velocity theory and the construction of shell damage evolution modes.

Numerical analysis of fracture in core-shell particle reinforced composites

The fracture of core-shell particle reinforced composites was simulated using a crack phase field method. A pre-existing crack may grow along the interface between the core and shell (core debonding), may penetrate the shell and the core (trans-core fracture), or may grow in the matrix (brittle fracture in the matrix). Shell fracture behaviours resulting from the competition between the fracture resistance and fracture driving force are crucial to the crack growth mechanisms. It was found that moderate strength and low modulus of the shell favoured trans-core fracture, and low strength and high modulus of the shell favoured core debonding. The effects on the overall mechanical properties were also identified. The composite strength usually benefited from stiffer and tougher components, regardless of the crack growth mechanisms, while the composite toughness was more complex. The toughening effect was highly related to how the crack evolved, as core debonding improved the toughness at the significant cost of strength, and trans-core fracture contributed most to the toughness with a slight reduction in strength compared with the matrix. These findings indicate design strategies for epoxy composites which can achieve a balance of strength and toughness, enabling the design of safer lightweight composites for electric vehicles and transport applications.

Osteoporosis and Bone Deformities in Free-Living Geoffroy's Toadhead Turtles (Phrynops geoffroanus) Rescued from Urban Areas in the Metropolitan Region of Recife (Pernambuco, Brazil)

Abstract Organic pollutants have bioaccumulative effects and induce a high index of toxicity in aquatic ecosystems. The aim of our study was to report tomographic abnormalities found in free-living turtles (Geoffroy`s toadhead turtle, Phrynops geoffroanus) from an urban area near the Capibaribe and Beberibe river basins in Brazil, which are known to be contaminated by heavy metals as well solid waste. Clinical and tomographic evaluation of eight turtles was performed to assess their health status for subsequent release. Tomographic analysis revealed bone abnormalities including demineralization, coarse trabecular pattern, subperiosteal bone resorption, deformity of dorsal vertebrae and shell fracture. Considering that turtles are recognized as bioindicators of water quality, a high occurrence of bone abnormalities may suggest an association with environmental pollution in the studied area and signal that conservation initiatives are needed to safeguard the aquatic ecosystem of the metropolitan region of Recife.

Metabolic profiling of Mytilus coruscus mantle in response of shell repairing under acute acidification.

Mytilus coruscus is an economically important marine bivalve mollusk found in the Yangtze River estuary, which experiences dramatic pH fluctuations due to seasonal freshwater input and suffer from shell fracture or injury in the natural environment. In this study, we used intact-shell and damaged-shell M. coruscus and performed metabolomic analysis, free amino acids analysis, calcium-positive staining, and intracellular calcium level tests in the mantle to investigate whether the mantle-specific metabolites can be induced by acute sea-water acidification and understand how the mantle responds to acute acidification during the shell repair process. We observed that both shell damage and acute acidification induced alterations in phospholipids, amino acids, nucleotides, organic acids, benzenoids, and their analogs and derivatives. Glycylproline, spicamycin, and 2-aminoheptanoic acid (2-AHA) are explicitly induced by shell damage. Betaine, aspartate, and oxidized glutathione are specifically induced by acute acidification. Our results show different metabolic patterns in the mussel mantle in response to different stressors, which can help elucidate the shell repair process under ocean acidification. furthermore, metabolic processes related to energy supply, cell function, signal transduction, and amino acid synthesis are disturbed by shell damage and/or acute acidification, indicating that both shell damage and acute acidification increased energy consumption, and disturb phospholipid synthesis, osmotic regulation, and redox balance. Free amino acid analysis and enzymatic activity assays partially confirmed our findings, highlighting the adaptation of M. coruscus to dramatic pH fluctuations in the Yangtze River estuary.

Transcriptomic response of Mytilus coruscus mantle to acute sea water acidification and shell damage

Mytilus coruscus is an economically important marine calcifier living in the Yangtze River estuary sea area, where seasonal fluctuations in natural pH occur owing to freshwater input, resulting in a rapid reduction in seawater pH. In addition, Mytilus constantly suffers from shell fracture or injury in the natural environment, and the shell repair mechanisms in mussels have evolved to counteract shell injury. Therefore, we utilized shell-complete and shell-damaged Mytilus coruscus in this study and performed transcriptomic analysis of the mantle to investigate whether the expression of mantle-specific genes can be induced by acute seawater acidification and how the mantle responds to acute acidification during the shell repair process. We found that acute acidification induced more differentially expressed genes than shell damage in the mantle, and the biomineralization-related Gene Ontology terms and KEGG pathways were significantly enriched by these DEGs. Most DEGs were upregulated in enriched pathways, indicating the activation of biomineralization-related processes in the mussel mantle under acute acidification. The expression levels of some shell matrix proteins and antimicrobial peptides increased under acute acidification and/or shell damage, suggesting the molecular modulation of the mantle for the preparation and activation of the shell repairing and anti-infection under adverse environmental conditions. In addition, morphological and microstructural analyses were performed for the mantle edge and shell cross-section, and changes in the mantle secretory capacity and shell inner film system induced by the two stressors were observed. Our findings highlight the adaptation of M. coruscus in estuarine areas with dramatic fluctuations in pH and may prove instrumental in its ability to survive ocean acidification.

Typical fracture modes of metal cylindrical shells under internal explosive loading

The competition and coupling of various fracture modes, including tensile fracture, shear fracture and spallation, exist in explosively-driven metal shells. However, the fracture mechanisms and influencing factors of different fracture modes are still unclear. In this study, three typical fracture modes of explosively-driven metal shells–tensile fracture, tensile-shear fracture and shear fracture are numerically revealed by using both the maximum principal strain and the Johnson-Cook cumulative-damage failure criterion. The selection of failure criteria is explained in detail. The fracture strain and fragment morphology are in good agreement with the experimental results. Combined with failure criterion, the numerical results are analyzed from the perspective of pressure, stress and strain. It is found that the formation of different fracture modes depends on the competition between the shear failure formed in the inner surface of the shell and the tensile micro-cracks formed in the middle of the shell. To further investigate the influencing factors of different fracture modes, three dimensionless parameters affecting the fracture modes are proposed based on dimensional analysis. In addition, by analyzing 29 sets of experimental data, we propose the dimensionless equations that can control different fracture modes. And the distribution diagrams of three typical fracture modes (tensile, tensile-shear and shear fracture) of explosively-driven metal shells are determined. Furthermore, we propose a parameter that can effectively distinguish adiabatic shear fracture from non-adiabatic shear fracture.

Mechanical impact characteristics of hollow shell granule based on continuous damage theory

Walnut, which is one of specific hollow shell granules, is inevitably subjected to damage deriving from repeated impacts in postharvest and processing. In this regard, the existence of damage was validated through force-deformation profile. The damage model was established and validated, respectively. Effects of walnut size and impact energy on damage behaviors, including damage variable characterizing degree of damage and damage accumulative coefficient describing sensibility to damage, were discussed, respectively. Results indicate that damage model by repeated impacts has been demonstrated to be valid for walnut shell fracture, in a way that is relatively independent of specific impact energy, only varying with walnut size. There exists a threshold size determining fracture mechanisms. Below threshold size, it is due to damage driving initial micro-crack gradually occurs, whereas beyond threshold size, it attributes to losing structural stability. The piecewise function between damage accumulation coefficient and walnut size was established.

The effect law of shell surface crack propagation under implosion loading

The fracture process of the metal cylindrical shell under the action of implosion is numerically simulated by AUTODYN finite element software for the expansion of cracks on the surface of the cases under the action of implosion loading. Numerical computations were used to determine the effect law of engineering factors such as the energy density of explosives, shell thickness, and shell material on crack-related parameters. The results show that the shell fracture radius along the axial direction remains nearly constant, and its value is less influenced by the energy density of explosives. The axial crack propagation velocity of the shell from the location of crack initiation to the non-exploding end of the shell shows a trend of change from high to low, fluctuating down. The axial crack propagation velocity and crack circumferential density both increase with the explosive energy density. The fracture density fluctuation range is between 0.4~0.73/mm. The law can be used to study the fracture damage of metal cylindrical shell structures under high impact.

Fatigue Life Analysis of Annular BOP Shell with Eccentric Wear Defect

The annular blowout preventer is impacted by the high pressure oil and gas in the well during its operation, and the shell may produce cracking cracks at the stress concentration part under the fatigue damage and periodic load, and the expansion in the long-term service will lead to the sudden fracture of the blowout preventer shell and fatigue damage. In order to analyze the factors affecting the fatigue life of annular BOP shell under eccentric wear damage, the initial defects of different shapes were applied to the FH35-35/70 annular BOP shell made of 25CrNiMo material, and its fatigue life was simulated.

Use of Computed Tomography in Evaluation and Management of Shell Fracture in a Red Eared Slider Turtle ( Trachemys scripta elegans) A Case report

Traumatic lesions of the shell are common problems in chelonians. Lesions of the shell vary in severity from a simple superficial abrasion (with a loss of the external skin layer and exposure of the bone) to complicated fractures of the carapace with exposure of internal organs of the coelom and injury of the soft tissues (Barten, 2006). In most shell or skeletal injuries in the turtle, plain radiographic data do not reveal the extent of complex fractures due to superimposed bone structures (Abou-Madi et al., 2002). In Comparison with conventional radiography, computed tomography (CT) allows better distinction of specific tissue densities and discrete changes in organ size, shape, margin, contour and position (Gaudron et al., 2001). Computed tomography is a non-invasive, cross-sectional diagnostic imaging technique that offers significant advantages for detection of pathologies in chelonians, and is ideal for diagnosing skeletal and soft tissue abnormalities (Gumpenberger and Henninger, 2001). The aim of the present work was to evaluate the three dimensional computed tomography (CT) for clinical examination of shell lesions in a red eared slider turtle.

Effect of the shell thickness on the mechanical properties of arrays composed of hybrid core-shell Si/SiC nanoparticles with overlapped shells

Atomistic simulations of quasi-static compression and tension of linear arrays consisting of hybrid spherical nanoparticles (NPs) with Si cores and 6H-SiC partially overlapped shells are performed to reveal the effect of the shell thickness on the deformation mechanism and mechanical properties of such NP arrays. The overlapped shells are considered as a model of a continuous coating that promotes the mechanical integrity of a nano-powder and transforms it into a porous composite material. At compression, the transition from ductile to brittle deformation behavior with increasing shell thickness is observed. The compression of a NP array with thick shells induces the formation of a quasi-conical slip surface. The fracture of a NP array at compression involves the fracture of both shell and core materials and can induce the formation of a new β-Sn phase in the Si core. At tension, the deformation process is characterized by a relatively large proportional limit, and the fracture occurs in the weak cross sections at the necks between NPs, so that the NP cores remain intact after fracture. Before fracture, the largest microscopic stresses are observed in the shell material near the core-shell interface. The simulations predict a strong increase of modulus and strength at tension and compression with an increase in the relative shell thickness, the ratio of the shell thickness to the NP diameter, while the effect of the NP size on mechanical properties is relatively weak. This suggests that the relative shell thickness is the major similarity parameter that dominates the mechanical properties of the NP arrays. Interestingly, the simulations predict a larger modulus for NPs with thick shells compared to single-material SiC NPs. This points at a non-trivial role of the core-shell interface and the degree of the shell overlap in the load transfer in the arrays of NPs with overlapped shells.

Construction and Verification of Spherical Thin Shell Model for Revealing Walnut Shell Crack Initiation and Expansion Mechanism

Walnut shell breaking is the first step of deep walnut processing. This study aims to investigate the mechanical properties and fracture state of the Qingxiang walnut shell under unidirectional load and guide the complete separation of the walnut shell and kernel. The spherical thin shell model of the walnut (the fitting error is less than 5%) was established and verified. The process from the initiation to the expansion of walnut cracks was analyzed. The crack expansion rate was estimated in terms of the crack fracture regularity on the shell’s surface. Based on the momentless theory and finite element simulation analysis, we found that the stress on the shell surface in the concentrated force action region was gradient distributed from inside to outside and that the internal forces were equal in all directions in the peripheral force action region. The unidirectional impact shell-breaking experiments confirmed the reliability of our spherical thin shell model and verified our hypothesis of walnut shell fracture along the longitudinal grain. Our results can provide a theoretical basis for the development and structural optimization of shell-breaking machinery.

Numerical study on the dynamic fracture of explosively driven cylindrical shells

Research on the expansion and fracture of explosively driven metal shells has been a key issue in weapon development and structural protection. It is important to study and predict the failure mode, fracture mechanism, and fragment distribution characteristics of explosively driven metal shells. In this study, we used the finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method and the fluid–structure interaction method to perform a three-dimensional numerical simulation of the expansion and fracture of a metal cylindrical shell. Our method combined the advantages of the FEM and SPH, avoiding system mass loss, energy loss, and element distortion; in addition, the proposed method had a good simulation effect on the interaction between detonation waves and the cylindrical shell. The simulated detonation wave propagation, shell damage morphology, and fragment velocity distribution were in good agreement with theoretical and experimental results. We divided the fragments into three regions based on their shape characteristics. We analyzed the failure mode and formation process of fragments in different regions. The numerical results reproduced the phenomenon in which cracks initiated from the inner surface and extended to the outer surface of the cylindrical shell along the 45° or 135° shear direction. In addition, fragments composed of elements are identified, and the mass and characteristic lengths of typical fragments at a stable time are provided. Furthermore, the mass and size distribution characteristics of the fragments were explored, and the variation in the fitting results of the classical distribution function under different explosion pressures was examined. Finally, based on mathematical derivation, the distribution formula of fragment velocity was improved. The improved formula provided higher accuracy and could be used to analyze any metal cylindrical shells with different length-to-diameter ratios.

Numerical Simulation Study of Expanding Fracture of 45 Steel Cylindrical Shell under Different Detonation Pressure.

Detonation and fragmentation of ductile cylindrical metal shells is a complicated physical phenomenon of material and structural fracture under a high strain rate and high-speed impact. In this article, the smoothed particle hydrodynamics (SPH) numerical model is adopted to study this problem. The model’s reliability is initially tested by comparing the simulation findings with experimental data, and it shows that different fracture modes of cylindrical shells can be obtained by using the same model with a unified constitutive model and failure parameters. By using this model to analyze the explosive fracture process of the cylindrical shells at various detonation pressures, it shows that when the detonation pressure decreases, the cylindrical metal shell fracture changes from a pure shear to tensile–shear mixed fracture. When the detonation pressure is above 31 GPA, a pure shear fracture appears in the shell during the loading stage of shell expansion, and the crack has an angle of 45° or 135° from the radial direction. When the pressure is reduced to 23 GPA, the fracture mode changes to tension–shear mixing, and the proportion of tensile cracks is about one-sixth of the shell fracture. With the explosion pressure reduced to 13 GPA, the proportion of tensile cracks is increased to about one-half of the shell fracture. Finally, the failure mechanism of the different fracture modes was analyzed under different detonation pressures by studying the stress and strain curves in the shells.

Semi-aromatic polyamide membrane incorporated with yolk-shell mesoporous hybrid nanospheres for ultrahigh permeability and improving comprehensive property

In this report, yolk-shell (YS) organic-inorganic hybrid nanospheres (YSHNs) with radially ordered mesopores were synthesized by a co-assembly strategy using 1,2-bis(triethoxysilyl)ethane and tetraethoxysilane as precursors, and cetyltrimethylammonium bromide as a soft template. Then, Silver nanoparticles (AgNPs) were uniformly embedded in the hollow cavities of the YSHNs. The semi-aromatic polyamide (SAP) based nanocomposite membrane was fabricated using 1,3,5-cyclohexane tricarbonyl chloride as an organic phase, meta-phenylene diamine as an aqueous phase, and the mesoporous YS hybrid nanospheres as nanoadditives by an interfacial polymerization approach. The results show that the YS nanospheres were successfully incorporated into the polyamide (PA) separation layer, and the membrane becomes very hydrophilic. The membrane incorporated with the aminated YS mesoporous nanospheres exhibits ultrahigh pure water permeability (PWP, 9.34 L m−2 h−1 bar−1) and comparable NaCl rejection (96.1%), which is dramatically higher than the membrane with common mesoporous nanospheres. It is because that the hollow cavity of the YS nanosphere further decreases the membrane resistance, and the aminated spherical surface improves the interfacial compatibility between the PA matrix and the YS nanospheres. Furthermore, the flexible YS hybrid structure and the mesoporous core could play an important buffering for avoiding the shell fracture under a high operation pressure. The chlorine resistance of the YS-nanosphere incorporated membrane is significantly improved compared to the pristine SAP membrane in a strong chlorination strength (5500 ppm h, pH = 5). The confined AgNPs in the YS mesostructure endow the membrane with a sustainable antibiofouling property. Moreover, the polylysine modification improves the membrane fouling resistance and performance stability.

Distribution of shear fragments classified by morphology

In studies on metal shell under internal explosive loading, unlike brittle metals, ductile metals usually exhibit shear fracture. Existing literature mostly focuses on slip fracture caused by unidirectional shear fracture, in fact, the shell fractures in the two directions of maximum shear stress, making morphology of the fragments diversified, considering fragment morphology in the distribution may achieve a better description. In previous studies, Poisson mixtures and Weibull mixtures model are only used for fragment distribution statistics as a functional form, and parameters (weight coefficient and distribution modulus) in the function lack physical process description. In this paper, an experimental study on the fragmentation of 50SiMnVB steel shell under TNT internal explosive loading was carried out. Through the observation and analysis of recovered fragments, the shear fragments with cross-sections of parallelogram, right-angled trapezoid, and isosceles right-angled triangle are divided into three types: A, B, and C. According to “A-type fragments created by the parallel through-the-thickness fractures, B-type and C-type fragments created by interaction of intersecting fractures,” the morphological parameters of fragments in the distribution model were derived, including fragment size (width, length, thickness, mass, etc.), shape parameters, and weight coefficient. Weibull mixture distribution model is used to describe the distribution of the total fragments, whereas Weibull distribution is used to describe the distribution of each type of fragment. Through the comparison of theoretical calculations and experimental data, the applicability of the theoretical model in the field of “shear fracture of ductile steel shell under internal explosive loading” is verified.

Spherical Al-Zr alloy powders prepared by centrifugal atomization for tunable energetic behavior

To improve the energetic behavior of Al, heterogeneous Al-Zr alloy powders were prepared by high-speed centrifugal atomization in this paper, the phase composition of which is Al and Al3Zr. The thermal analysis results show that the main oxidation process of Al-Zr occurs at 800 °C–1200 °C. The oxidation peak temperature of the alloy is 25 °C lower than that of Al, accompanied with a higher weight gain and faster oxidation rate. Besides, the activation energy (Ek) is significantly reduced by 74 kJ/mol. Compared with Al/CuO, the ignition delay of Al-Zr/CuO is shortened by 0.6 ms, and the reaction temperature is advanced by 29 °C. This is due to the earlier concentrated heat release of Al3Zr and the grain refinement of Al-Zr that aggravates the shell fracture and result in more intense oxidation of the alloy powders. Therefore, Al-Zr alloy powders possess a significantly enhanced combustion performance than Al.

Testing Explosive Materials for Sensitivity to Mechanical Impact by the Shell Fracture Method

Testing Explosive Materials for Sensitivity to Mechanical Impact by the Shell Fracture Method