Strength Of Shells Research Articles

Parasites disrupt a keystone mutualism that underpins the structure, functioning, and resilience of a coastal ecosystem

AbstractParasites can alter the traits or densities of mutualistic partners, potentially destabilizing mutualistic associations that underpin the structure, functioning, and stability of entire ecosystems. Despite the potentially wide‐ranging consequences of such disruptions, no studies have directly manipulated parasite prevalence and/or intensity in a mutualistic partner, nor quantified the resulting community‐level effects. Here, we investigated the effects of a common trematode parasite (Cercaria opaca) on the strength of a keystone facultative mutualism in western Atlantic salt marshes between the foundational marsh cordgrass, Spartina alterniflora, and the ribbed mussel, Geukensia demissa. Cordgrass increases mussel survivorship and growth through shading, while mussels enhance cordgrass growth by producing nutrient‐rich biodeposits. This mutualistic association also creates conditions that enhance biodiversity and ecosystem functioning, and mediates the ability of foundational plants to resist and recover from extreme drought. We used lab and field assays to show how increasing infection with trematode metacercariae negatively influenced mussel biodeposit production, as well as the strength of mussel shells and byssal attachments. By conducting a field manipulation using experimentally infected mussels, we demonstrated that the mutualistic benefits of mussels to cordgrass growth decreased with increasing trematode infection intensity—a pattern likely generated by reduced mussel biodeposition and enhanced mortality. Additionally, increasing parasite loads in mussels led to predictable decreases in the abundances of benthic invertebrates, as well as in key ecosystem characteristics and process rates (i.e., redox potential and sediment accretion). Finally, a survey of five North Carolina salt marshes demonstrated that infection with C. opaca was most common in mussels in areas experiencing cordgrass die‐off due to drought, and that infection intensity decreased with distance from die‐off areas. Because the mussel–cordgrass mutualism underpins marsh ecosystem resilience to drought‐associated die‐off, our results suggest that parasitism may depress recovery from these disturbances. Although this is the first experimental demonstration of parasites indirectly altering community structure and functioning by undermining an ecologically influential mutualism, this type of relationship could be common in nature, given that parasites frequently infect influential mutualists.

Ocean acidification will not affect the shell strength of juveniles of the commercial clam species Chamelea gallina: Implications of the local alkalinization of seawater

Ocean acidification (OA) is expected to decrease the strength of bivalves’ shells, especially during the early stages of development, with negative consequences to the resilience of natural populations and the economy. The objectives of the present study were to assess the long-term effect of increasing pCO2 after 217 days of exposure under controlled conditions of pH of ∼8.2, 8.0, and 7.7 on the strength and integrity of shells of juveniles of the commercial striped venus clam Chamelea gallina. Shell strength was estimated through compression tests and integrity through scanning electron microscopy (SEM) and dispersive X-ray analyses (EDX). The results showed that under increasing pCO2 the shell strength of juveniles is unaffected, which could be related to the locally elevated total alkalinity of seawater with respect to other parts of the coastal lagoon. However, despite this, it was also observed that the juvenile clams exposed to elevated pCO2 decreased their shell thickness and increased the porosity of their prismatic layer. Under future OA conditions, these changes could eventually compromise the integrity of the shells, becoming more vulnerable to the attack of predators and breakable during fishing operations. Future studies should address the plasticity of the organisms and the effect of the alkalinization of seawater on the resilience of shellfish juveniles under global change conditions.

Enhanced comprehensive properties of alumina ceramic shells by a pennisetum fiber/AlF3•3H2O powder hybrid system

The strength and permeability to gas of ceramic shells are key factors affecting the quality of castings. This research aims to improve the properties of alumina-based ceramic shells (i.e., Al2O3 and SiO2) using a combination of pennisetum fiber and AlF3•3H2O powder. The pennisetum fiber can improve the green strength of ceramic shells, while AlF3•3H2O powder can improve the high-temperature strength of ceramic shells by inducing the generation of mullite (3Al2O3•2SiO2) whiskers at high temperatures. Meanwhile, the mixture of pennisetum fibers and mullite whiskers can also improve the permeability to gas of the ceramic shell. As a result, the modified ceramic shell shows a clear increase in the above-mentioned properties, including 43 % of the green strength, 100 % of the permeability to gas, and 30 % of the thermal diffusion coefficient. In addition, the high-temperature bending strength and deformation under the weight of the ceramic shells are also obtained.

Physical correction factor in ultimate strength calculation of deep-sea pressure-resistant cylindrical shells made of TC4, Ti80 and 18Ni(250)

ABSTRACT The increase in design depth of deep-sea equipment leads to new requirements for material selection criterion, so it is necessary to pay attention to the rationality of the coefficient values in the design formula based on material performance. In this paper, based on three candidate high-strength materials, TC4, Ti80 and 18Ni(250), a number of pressure-resistant cylindrical shell calculation models are designed according to the pressure vessel code, and the physical correction coefficients, Cs, in the calculation of the ultimate strength of the cylindrical shells are derived through theoretical and finite element calculations. The results are compared with the curve recommended by the China Classification Society as well as finite element analysis results. The deviations and material suitability between different methods are clearly demonstrated. The theoretical calculation basis for three alternative materials for pressure-resistant shells is extended, thus compensating for the small range of material applicability in current submersible specifications.

Collaborative optimization of a composite pressure cylindrical shell based on dynamic penalty functions

This article reports the design and optimization of pressure cylindrical shells comprising carbon/epoxy and glass/epoxy composite materials. It presents a method for analyzing the pressure cylindrical shells of composite materials, analyzes the strength and buckling of composite pressure cylindrical shells with different rib numbers, and investigates the influence of thickness and ply angles ([±θ]10 and [903(±θ)2903]) on the critical buckling and strength-failure stresses. An approximate model of composite pressure cylindrical shells and collaborative optimization based on dynamic penalty functions are combined into a multidisciplinary optimization framework of composite pressure cylindrical shells. The optimization aims to maximize the critical buckling stress while minimizing the buoyancy coefficient. At a buoyancy coefficient similar to that of the initial scheme, the critical buckling stresses of the carbon/epoxy and glass/epoxy cylindrical shells increased by 21.85% and 9.5%, respectively, verifying the effectiveness of the collaborative optimization framework based on dynamic penalty functions.

Static Stability Behavior-Based Seismic Damage Endurance Assessment of Long-Span Single-Layer Spherical Lattice Shells

ABSTRACT This paper presents a modified evaluation approach for the structural-capacity-reserve (SCR) based on the static stability behavior of single-layer spherical lattice shells to achieve more accurate assessment results of seismic damage endurance. The SCR index in this paper is calculated by integrating the redefined residual structural capacity (RSC) ratio based on post-earthquake static stability behavior within the range of damage degrees caused by strong earthquakes. Compared with the assessment work for seismic damage endurance in the existing literature, the proposed RSC ratio in this paper could take into account both ultimate load-bearing strength and residual deformation. Additionally, the specific quantitative indicator in the proposed assessment method should also be determined according to whether the residual nodal displacement of the lattice shell after an earthquake exceeds the limit value state specified by the design code. The numerical results in the case study indicate that the residual load-bearing strength of the lattice shell remains relatively constant under the same damage state induced by different earthquakes, with residual deformation significantly impacting the assessment of seismic damage endurance. Thereby, the required RSC can be controlled by reducing the residual nodal displacements of the lattice shell under strong earthquakes to achieve a well-balanced design scheme.

Exploring the potential of pulverized oyster shell as a limestone substitute in limestone calcined clay cement (LC3) and its implications for performance

With the advent of rapid climate change and global warming, the cement industry has been actively striving to minimize its carbon footprint. An effective approach for reducing carbon emissions is to utilize supplementary cementitious materials (SCMs). Limestone calcined clay cement (LC3) has garnered significant attention because of its ability to reduce clinker use by approximately 45 wt%, compared to ordinary Portland cement. However, the raw materials involved in LC3 production, which are obtained through mining and heating of raw clay, also counts toward the carbon footprint. Therefore, the present study aims to explore the feasibility of using oyster shells as a replacement for limestone in LC3 systems. Various amorphousness of calcined clay were tested to investigate the hydration reaction and strength of the oyster shell calcined clay cement (OC3). Data collected using techniques such as X-ray diffraction, thermogravimetry, scanning electron microscopy, isothermal calorimetry, compressive strength testing, and 29Si nuclear magnetic resonance spectroscopy were analyzed to elucidate the hydration reaction mechanisms of OC3, considering the type of calcite (oyster shell or limestone) and the extent of the transformation of kaolinite clay to metakaolin. The findings of this study demonstrate that oyster shells can effectively replace limestone as a raw material for LC3. Furthermore, the irregular morphology of the shell particles enhanced the hydration reaction and development of the cement’s microstructure.

Effect of local loading on microstructure and enhanced mechanical property of large complex castings prepared by Al–Si–Fe–Mn–Mg–Cu alloy during squeeze casting

Flywheel shells with a complex structure and large wall-thickness difference, as key components in heavy trucks, serve to connect the engine and transmission. Formability and mechanical performance control of such components should be taken into consideration. In this work, an Al–Si–Fe–Mn–Mg–Cu alloy was used to manufacture the flywheel shell via squeeze casting. The role of local loading on microstructure and mechanical property at thick-walled positions was investigated. Furthermore, the effect of the squeeze casting specific pressure and heat treatment on the microstructure and mechanical property of the Al–Si–Fe–Mn–Mg–Cu alloy flywheel shells was also analyzed. The results showed that at the thick-walled positions, local loading not only helped eliminate the solidification defects, but also refined the microstructure including α-Al grains and secondary dendrite arm spacing. With increasing the squeeze casting specific pressure from 24 MPa to 32 MPa, microstructure refinement and mechanical property enhancement of squeeze casting flywheel shells were obtained. After T6 heat treatment, the yield strength and ultimate tensile strength of flywheel shells were further increased to 261.8 and 318.4 MPa, respectively, owing to the formation of spherical eutectic Si phases and nano-sized β'', Q and S precipitates.

Insight into the tribological performances of coconut shells as a potential natural water lubrication material

To better understand the tribological performance of coconut shell and to demonstrate its potential as a wear-resistant material for use in a water-lubricated environment, the microstructure of coconut shell was hereby characterized, and its hardness and water absorption properties were correspondingly measured. The tribological characteristics of coconut shells rubbing against a ZrO2 ceramic ball in dry and wet environments were studied, and the wear mechanism was revealed. The measurement characterization and experimental results indicate that the long axis of coconut shell ellipsoid cells grows along the direction of the long axis pointing towards the coconut shell ellipsoid, but this directionality has a relatively small impact on the tribological properties. The average sliding friction coefficient of coconut shell rubbing against ZrO2 ceramic balls is about 0.52 and 0.095, respectively under dry and wet friction conditions. Under dry friction conditions, the wear of coconut shells is mainly because of cell tearing, detachment and abrasive wear caused by alternating friction forces. Mainly considering the combined effects of the high hardness, high strength and good water absorption of coconut shells, as well as the water film at the friction interface, the friction force significantly reduces and makes it difficult to damage the cell structure, leading to a wear rate decrease by more than 100 times under wet friction conditions, much lower than that of lignum vitae. Overall, this study indicates the potential of coconut shell as a water lubricated friction pair material featuring excellent performance.

Normal Mode Solutions of Target Strengths of Solid-filled Spherical Shells and Discussion of Influence Parameters

The normal mode solution for the form function and target strength (TS) of a solid-filled spherical shell is derived. The calculation results of the spherical shell’s acoustic TS are in good agreement with the results of the finite element method (FEM). Based on these normal mode solutions, the influences of parameters such as the material, radius, and thickness of the inner and outer shells on the TS of a solid-filled spherical shell are analyzed. An underwater spherical shell scatterer is designed, which uses room temperature vulcanized (RTV) silicone rubber as a solid filling material and does not contain a suspension structure inside. The scatterer has a good TS enhancement effect.

Strength Analysis of Cylindrical Shells with Tangential Nozzles under Internal Pressure

Pressure vessels having the structure of a cylindrical shell with a tangential nozzle are often used in engineering for some process requirements. But there are no accurate methods in engineering codes for the strength design of this special structure. In this paper, the limit–load analysis was performed to evaluate the weakening effects of the tangential nozzles on the strength of the cylindrical shells under internal pressure. A so-called strength–weakening coefficient was defined to reflect the weakening degree of the load-bearing capacity of the cylindrical shells by the tangential nozzles or specifically by the three dimensionless structural parameters, namely diameter ratio (do/Di), diameter-thickness ratio (Di/T) and thickness ratio (t/T). Results show that when increasing do/Di and Di/T or decreasing t/T, the strength–weakening coefficient increases, which means that the strength–weakening effect of the tangential nozzle on the cylindrical shell increases. With sufficient simulation results, regression equations for the strength–weakening coefficient were obtained which provides a reference for the strength design of cylindrical shells with tangential nozzles under internal pressure.

Study on the Ultimate Load Failure Mechanism and Structural Optimization Design of Insulators.

This study aims to enhance the productivity of high-voltage transmission line insulators and their operational safety by investigating their failure mechanisms under ultimate load conditions. Destructive tests were conducted on a specific type of insulator under ultimate load conditions. A high-speed camera was used to document the insulator's failure process and collect strain data from designated points. A simulation model of the insulator was established to predict the effects of ultimate loads. The simulation results identified a maximum first principal stress of 94.549 MPa in the porcelain shell, with stress distribution characteristics resembling a cantilever beam subjected to bending. This implied that the insulator failure occurred when the stress reached the bending strength of the porcelain shell. To validate the simulation's accuracy, bending and tensile strength tests were conducted on the ceramic materials constituting the insulator. The bending strength of the porcelain shell was 100.52 MPa, showing a 5.6% variation from the simulation results, which indicated the reliability of the simulation model. Finally, optimization designs on the design parameters P1 and P2 of the insulator were conducted. The results indicated that setting P1 to 8° and P2 to 90.062 mm decreased the first principal stress of the porcelain shell by 47.6% and Von Mises stress by 31.6% under ultimate load conditions, significantly enhancing the load-bearing capacity. This research contributed to improving the production yield and safety performance of insulators.

An Experimental Study On Split Tensile Strength Of M30 Concrete Using Novel Seashell Powder And Egg Shell Powder As A Partial Replacement Of Fine Aggregate In Comparison With Conventional Concrete

Aim: The study's goal is to compare the Split Tensile Strength of Novel Seashell and Egg Shell based Powder M30 concrete and conventional concrete. Materials and Methods: There are two categories taken into account. Concrete with egg and seashell powders is in group 1, while standard concrete is in group 2. There are 18 samples in each group, for a total of 36 sample sizes. The preparation and examination of the samples involved using a variety of tools and materials. Result: The independent sample T-test is carried out using SPSS software, version 21, was used. The mean Split Tensile Strength of conventional concrete sample is 3.59 N/mm2, but the mean Split Tensile Strength of novel seashell and egg shell-based Powder M30 concrete is 4.87 N/mm2. To assess the data, a T-test for independent samples is used. The mean values for the group statistical report were 3.5889 and 4.8411, and the independent t-test revealed a F value of 0.150. An independent sample t-test is performed on the two groups to see whether there is a significant difference, with g power set at 80% and p=0.000 (p0.05) as the cutoff. This indicates that there are statistical differences between the two groups considered in this study significantly from one another. Conclusion: The concrete with theNovel Seashell and Egg Shell based Powder M30 concrete had more Split Tensile Strength when compared the conventional concrete.

ELASTIC AND STRENGTH PARAMETERS DETERMINATION OF POLYMER COMPOSITE MATERIALS AND CYLINDRICAL SHELLS

The article presents a method for layout optimization in polymer composite materials that allows to assess their strength. In order to assess the stress-strain state of each layer, an orthotropic elasticity model is used assuming that the fibers in the material are parallel. The behavior model of polymer composite materials is based on the Hashin criterion, which makes it possible to separate the destruction mechanisms of matrix and fiber. The strength assessment was carried out in accordance with the structural approach involving studying the strength of each layer separately. The parameters of the deformation model and the Hashin strength criterion were determined based on the results of testing. Tests were carried out on unidirectional polymer composite materials samples cut at angles of 0, 90 and 45° to the direction of reinforcement. The verification was based on the results of bending tests of polymer composite materials samples. Verification showed high proximity between the calculation results and the experimental data. A method for selecting the layout angles of each layer of polymer composite materials has been developed making it possible to calculate the greatest strength of the cylindrical shell under various external loads. The method involves determining the stresses in each of the polymer composite materials layers, as well as Hashin indicators corresponding to the destruction of the fiber or matrix under tension or compression. Based on the indicator values, the optimal angle and layout pattern can be selected, providing the greatest margin of safety for the shell. This method allows for a preliminary assessment of the safety factor of cylindrical shells made of polymer composite materials based on the experimentally determined elastic parameters of the material and the parameters of the Hashin strength criterion. The method takes into account the angle and layout of the prepreg under the influence of internal pressure, axial compressive force and torque.

On the ultimate strength of heterogeneous slender structures based on multi-scale stress decomposition

This paper presents an algorithm based on asymptotic methods for computing the effective ultimate and high cyclic fatigue strength of heterogeneous periodic plates, shells, and textiles. The rigorous analysis and convergence proof of this asymptotic method builds upon a series of our previous papers. The method allows to decompose the local stresses as products of periodic stress-concentrations, given as functions of unit cells or graphs/lattices in them, and the macroscopic strain components.In addition, this paper establishes bounds for the applicability of the method and presents several examples to demonstrate the qualitative advantages of this approach, e.g. for the standard shear and compression tests for plates. The main objective of this paper is to substantially reduce the problem dimension and complexity, thereby enabling more efficient computations.

Ultimate state assessment of medium-thick composite cylindrical pressure shells based on progressive damage

The ultimate strength of medium-thick composite pressure shells under hydrostatic pressure was studied by experimental test and finite element method in this paper. The ultimate strength, damage form and strain response of cylindrical shells were obtained by hydrostatic destruction test, which carried out for two T700 carbon fiber/epoxy composite cylindrical pressure shells with different length. Meanwhile, finite element models were built to predict the strength failure pressure based on the progressive damage mechanism of composite materials and its initial defects. The finite element results were in close agreement with the experimental results. A parametric study was carried out to discuss the effect of radius-length ratio and radius-thickness ratio on ultimate strength. Based on the numerical results, an empirical formula was proposed as a function of radius-length ratio and radius-thickness ratio to predict the ultimate strength of medium-thick composite pressure shells.

Optimized Design of the Carrier Structure of an Autonomous Glide Marine Seismometer

Mobile Earthquake Recording in Marine Areas by Independent Divers (MERMAID) provides a possibility for long-term and large-scale observation of natural seismic P waves, but it does not have mobility and can only drift with ocean currents, resulting in observation equipment locations that are too sparse or too dense, both of which are not suitable for network observation. Therefore, this paper developed a new type of Autonomous Glide Marine Seismometer (AGMS) with mobility and the ability to adjust the observation position. The AGMS adopts a flying saucer shape, which has better hydrodynamic characteristics and better motion stability. This paper focused on the material, shape, and structure of the pressure-resistant shell for the selection of design and strength checking research. Using the finite element analysis method and introducing the initial defect, the results showed that the yield strength of the pressure-resistant shell decreases with the initial defect value. The calculation results were compared and analyzed with the relevant theoretical formulas and specification calculation results, and all the results met the design requirements. The results of this design could also provide reference for the design of related deep-sea pressure chambers.

Empirical formula to assess ultimate strength of side shell on passenger ship under combined axial and shear load based on experimental and numerical analysis

This study proposes an empirical formulation to assess the ultimate strength of side shells on passenger ships subjected to combined effects of axial compression and shear loads. The deteriorating effects of large openings and strengthening effects of stiffener reinforcements were considered in the proposed formulation for a wider range of applications. To verify accuracy of the empirical formula, an experimental test was first conducted to inspect the collapse behaviour and influential parameters of the side shell. More than 5000 side-shell scenarios were subsequently adopted as the input dataset based on the experimentally validated nonlinear finite element method. A simplified polynomial shape was proposed for the empirical formula by comparing various generation sets of the four-parameter-based formulations. A reliable solution to the proposed empirical formula was obtained with respect to a high determination coefficient compared to the numerical results. The developed empirical formula can be considered as applicable and beneficial for practical structural design work of side shells with large openings in modern passenger ships.

Seismic Resistance of Non-Linearly Deformable Large-Span Spatial Structures of Unique Buildings

Analytical, computer and experimental modeling methods are applied in the study of seismic resistance and changing dynamic parameters of long-term loaded non-linearly deformed large-span spatial shell structures. Physically and geometrically nonlinear deformation models and computational algorithms for solving dynamic problems are proposed for estimating the stress-strain state of smooth and ribbed spatial systems with variable stiffness caused by damage accumulation and orthotropic structure reinforced by ribs. The possibility of using the proposed method of taking into account variable dynamic stiffness in calculations for solving problems of dynamic strength and stability of spatial large-span shells of unique buildings of complex geometry is shown.

Main problems of mine drum design

Problem. The article deals with the problem of mine drums, namely, an adjusted approach to the justification of their design, and suggests ways to improve their operational properties. Mine drums ensure the reliable operation of the entire hoisting machine and often the safety of people themselves, so the topic discussed in the article is very relevant. Gool. The practice of designing mine drums is based on the use of elemental stiffeners, such as ribs, rings and braids. This significantly increases the weight and complexity of the drum manufacturing, and also leads to the appearance of local stresses at the welding points. In mine drums, not only the drum shell, but also the lining is loaded. Methodology. To increase their stiffness, they are reinforced with braids, which not only increases the weight of the drum itself, but also significantly complicates the technology. At the same time, the strength of the frontal lobes decreases, i.e. we have the opposite effect. This greatly complicates the operation of the structure and leads to the destruction of welds and cracks. Reinforcing the welds does not improve the situation, but, on the contrary, reduces the durability of the mine drum shell. Results. The calculations of the strength of the headwall by the simplified and refined methodology showed that the strength of the headwall is fully ensured and the need to install an additional structure in the form of scarves does not make sense. Originality. Additional factors were taken into account that were not considered in previous calculations, such as the stiffness of the headstays themselves and the coefficient of friction between the rope and the drum. Practical value. The application of the new methodology for calculating the strength of the mine rope drum shell proposed in this paper can significantly improve the operation of mine hoisting machines, reduce the number of repairs, and ensure their durability. In addition, the metal consumption of the drums is significantly reduced, which allows to obtain significant savings in their cost and ensure reliable operation of the entire mine hoisting process.