ULTIMATE LOAD-BEARING CAPACITY OF CYLINDER DERIVED FROM AUTOFRETTAGE UNDER IDEAL CONDITION

According to the basic theory on autofrettage and according to the 4th strength theory, several parameters and their relations are studied under ideal condition, including σej/σy, the equivalent stress of total stresses at elastoplastic juncture; σei/σy, the equivalent stress of total stresses at inside surface; σej＇/σy, the equivalent stress of residual stresses at elastoplastic juncture; σei＇/σy, the equivalent stress of residual stresses at inside surface; and p/σy, load-bearing capacity of an autofrettaged cylinder. By theoretical study on relations between the parameters, noticeable results and laws are achieved： to satisfy ｜σei＇｜=σy. the relation between kj and k is, k^2lnkj^2-k^2-kj^2＋2=0, when k→∞, kj = √e = 1.648 72, as based on the 3rd strength theory, where k is the outside/inside radius ratio of a cylinder, kj is the ratio of elastoplastic juncture radius to inside radius of a cylinder; If the plastic region covers the whole wall of a cylinder, for compressive yield not to occur after removing autofrettage pressure, the ultimate k is k=-2.218 46 as based on the 3rd strength theory; With k=2.218 46, a cylinder＇s ultimate load-bearing capacity equals its entire yield pressure, or p/σy=21nk/√3; The maximum and optimum load-bearing capacity of an autofrettaged cylinder is just 2 times the loading which an unautofrettaged cylinder can bear elastically, or p/σy=2（k^2-1）/√3 k^2, and the limit of the load-bearing capacity of an autofrettaged cylinder is also just 2 times that of an unautofrettaged cylinder. The conclusions are the same as based on the 3rd strength theory, but some equations are different from each other.

Effect of Optimum Plastic Depth on Stresses and Load-bearing Capacity of Autofrettaged Cylinder

Autofrettage is an effective measure to even distribution of stresses and raise load-bearing capacity for （ultra-）high pressure apparatus. Currently, the research on autofrettage has focused mostly on specific engineering problems, while general theoretical study is rarely done. To discover the general law contained in autofrettage theory, by the aid of the authors’ previous work and according to the third strength theory, theoretical problems about autofrettage are studied including residual stresses and their equivalent stress, total stresses and their equivalent stress, etc. Because of the equation of optimum depth of plastic zone which is presented in the authors’ previous work, the equations for the residual stresses and their equivalent stress as well as the total stress and their equivalent stress are simplified greatly. Thus the law of distribution of the residual stresses and their equivalent stress as well as the total stress and their equivalent stress and the varying tendency of these stresses are discovered. The relation among various parameters are revealed. The safe and optimum load-bearing conditions for cylinders are obtained. According to the results obtained by theoretical analysis, it is shown that if the two parameters, namely ratio of outside to inside radius, k, and depth of plastic zone, kj, meet the equation of optimum depth of plastic zone, when the pressure contained in an autofrettaged cylinder is lower than two times the initial yield pressure of the unautofrettaged cylinder, the equivalent residual stress and the equivalent total stress at the inside surface as well as the elastic-plastic juncture of a cylinder are lower than yield strength. When an autofrettaged cylinder is subjected to just two times the initial yield pressure of the unautofrettaged cylinder, the equivalent total stress within the whole plastic zone is just identically equal to the yield strength, or it is a constant. The proposed research theoretically depicts the stress state of ultra-）high pressure autofrettaged cylinder more accurately and more reasonably and provides the reference for design of （ultra-）high pressure apparatus.

Simulation and Experimental Study on Load-bearing Deformation Characteristics of 11R22.5 Vehicle Retreaded Tire

The finite element bearing deformation simulation was implemented on 11.00R22.5 retreaded tires by ANSYS software in the paper in order to further clarify the bearing deformation characteristics of retreaded tires and improve the performance of retreaded tires effectively.The characteristic laws of bearing radial deformation and bearing lateral deformation of retreaded tire and new tires of the same model under different working conditions were obtained through load deformation tests.The radial deformation calculation results,simulation results and measured results of retreaded tires were comparatively analyzed.The calculation formula of bearing radial deformation of retreaded tires was proposed based on the linear regression principle.The difference of bearing deformation characteristics and ground area characteristics of retreaded tires and new tires were comparatively analyzed.The results showed that the radial and lateral deformation of retreaded tires and new tires is increased with the increase of radial load when the tire pressure was constant,and the increase trend is approximately linear.The radial stiffness of retreaded tires is similar to that of new tires under certain tire pressure and low load.The radial stiffness of retreaded tires is larger than that of new tires,and the stiffness difference is increased with the increasing of load under constant tire pressure and high load.Rubber aging phenomenon in retreaded tire carcass have an impact on the bearing deformation characteristics of retreaded tires,thereby producing great impact on the remaining service life of retreaded tires.

Developing of Load-bearing Bones Replacement Based on Cerium Compounds/Nano-hydroxyapatite Composites

The importance of implantable biomaterials is growing up in recent days for modern medicine,especially fixation,replacement,and regeneration of load-bearing bones.Through the past several years,metals,ceramics,polymers,and their composites,have been used for the reconstruction of hard tissues.Special standards such as adequate mechanical and biocompatible properties are required to avoid rejection reactions of the tissues.Recently,a number of novel advanced biomaterials are developed as promising candidates.Amongst those,cerium-based biomaterials acquired attention as a substitution material for hard tissues reconstruction because of cerium antioxidative properties,which enabled it to be used to decrease mediators of inflammation.In addition,the eminent mechanical properties,as well as the perfect chemical and biological compatibilities,make cerium-based biomaterials attractive for biomedical application.

Additively manufactured Ti–Ta–Cu alloys for the next-generation load-bearing implants

Bacterial colonization of orthopedic implants is one of the leading causes of failure and clinical complexities for load-bearing metallic implants. Topical or systemic administration of antibiotics may not offer the most efficient defense against colonization, especially in the case of secondary infection, leading to surgical removal of implants and in some cases even limbs. In this study, laser powder bed fusion was implemented to fabricate Ti3Al2V alloy by a 1:1 weight mixture of CpTi and Ti6Al4V powders. Ti-Tantalum(Ta)–Copper(Cu) alloys were further analyzed by the addition of Ta and Cu into the Ti3Al2V custom alloy. The biological,mechanical, and tribo-biocorrosion properties of Ti3Al2V alloy were evaluated. A 10 wt.% Ta(10Ta) and 3 wt.% Cu(3Cu) were added to the Ti3Al2V alloy to enhance biocompatibility and impart inherent bacterial resistance. Additively manufactured implants were investigated for resistance against Pseudomonas aeruginosa and Staphylococcus aureus strains of bacteria for up to 48 h. A 3 wt.% Cu addition to Ti3Al2V displayed improved antibacterial efficacy, i.e.78%–86% with respect to CpTi. Mechanical properties for Ti3Al2V–10Ta–3Cu alloy were evaluated, demonstrating excellent fatigue resistance, exceptional shear strength, and improved tribological and tribo-biocorrosion characteristics when compared to Ti6Al4V. In vivo studies using a rat distal femur model revealed improved early-stage osseointegration for alloys with10 wt.% Ta addition compared to CpTi and Ti6Al4V. The 3 wt.% Cu-added compositions displayed biocompatibility and no adverse infammatory response in vivo. Our results establish the Ti3Al2V–10Ta–3Cu alloy’s synergistic effect on improving both in vivo biocompatibility and microbial resistance for the next generation of load-bearing metallic implants.

Ultra-low Friction and High Load-Bearing Hydrogel with Tubular Structure Based on Controllable Light-Induced Dissociation

With high water content,excellent biocompatibility and lubricating properties,and a microstructure similar to that of the extracellular matrix,hydrogel is becoming one of the most promising materials as a substitute for articular cartilage.However,it is a challenge for hydrogel materials to simultaneously satisfy high loading and low friction.Most hydrogels are brittle,with fracture energies of around 10 J·m^(-2),as compared with∼1000 J·m^(-2) for cartilage.A great deal of effort has been devoted to the synthesis of hydrogels with improved mechanical properties,such as increasing the compactness of the polymer network,introducing dynamic non-covalent bonds,and increasing the hydrophobicity of the polymer,all at the expense of the lubricating properties of the hydrogel.Herein,we develop a hydrogel material with anisotropic tubular structures where the compactness gradually decreases and eventually disappears from the surface to the subsurface,achieving a balance between lubrication and load-bearing.The porous layer with hydrophilic carboxyl groups on the surface exhibits extremely low friction(coefficient of friction(COF)∼0.003,1 N;COF∼0.08,20 N)against the hard steel ball,while the bottom layer acts as an excellent load-bearing function.What is more,the gradual transition of the tubular structures between the surface and the subsurface ensures the uniform distribution of friction stress between a lubricating and bearing layers,which endows the material with long-lasting and smooth friction properties.The extraordinary lubricious performance of the hydrogels with anisotropic tubular structure has potential applications in tissue engineering and medical devices.

Additive manufacturing of metallic and polymeric load-bearing biomaterials using laser powder bed fusion:A review

Surgical prostheses and implants used in hard-tissue engineering should satisfy all the clinical,mechanical,manufacturing,and economic requirements in order to be used for load-bearing applications.Metals,and to a lesser extent,polymers are promising materials that have long been used as load-bearing biomaterials.With the rapid development of additive manufacturing(AM)technology,metallic and polymeric implants with complex structures that were once impractical to manufacture using traditional processing methods can now easily be made by AM.This technology has emerged over the past four decades as a rapid and cost-effective fabrication method for geometrically complex implants with high levels of accuracy and precision.The ability to design and fabricate patient-specific,customized structural biomaterials has made AM a subject of great interest in both research and clinical settings.Among different AM methods,laser powder bed fusion(L-PBF)is emerging as the most popular and reliable AM method for producing load-bearing biomaterials.This layer-by-layer process uses a high-energy laser beam to sinter or melt powders into a part patterned by a computer-aided design(CAD)model.The most important load-bearing applications of L-PBF-manufactured biomaterials include orthopedic,traumatological,craniofacial,maxillofacial,and dental applications.The unequalled design freedom of AM technology,and L-PBF in particular,also allows fabrication of complex and customized metallic and polymeric scaffolds by altering the topology and controlling the macro-porosity of the implant.This article gives an overview of the L-PBF method for the fabrication of load-bearing metallic and polymeric biomaterials.

Towards a Medium/High Load-Bearing Scaffold Fabrication System

This paper describes fabrication of scaffolds for load-bearing applications, with primary consideration from the manufacturing perspective. An extrusion device, inspired by the FDM process, was used to create scaffolds from a variety of different polymeric materials and mixtures. The effectiveness of these scaffolds to host cells for bone regeneration has been investigated. This ongoing work has generated significant insight into the future direction of research and the possibilities of developing scaffolds for medium/high load-bearing applications.

Porous metal implants: processing,properties, and challenges

Porous and functionally graded materials have seen extensive applications in modern biomedical devices—allowing for improved site-specific performance;their appreciable mechanical,corrosive,and biocompatible properties are highly sought after for lightweight and high-strength load-bearing orthopedic and dental implants.Examples of such porous materials are metals,ceramics,and polymers.Although,easy to manufacture and lightweight,porous polymers do not inherently exhibit the required mechanical strength for hard tissue repair or replacement.Alternatively,porous ceramics are brittle and do not possess the required fatigue resistance.On the other hand,porous biocompatible metals have shown tailorable strength,fatigue resistance,and toughness.Thereby,a significant interest in investigating the manufacturing challenges of porous metals has taken place in recent years.Past research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized,their biological and biomechanical compatibility—with the host bone—has been followed up with extensive methodical research.Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review,specifically,how the manufacturing process influences microstructure,graded composition,porosity,biocompatibility,and mechanical properties.Most of the studies discussed in this review are related to porous structures for bone implant applications;however,the understanding of these investigations may also be extended to other devices beyond the biomedical field.

Experimental Investigation on Durability of Reinforced Concrete Beams in A Simulated Marine Environment

This paper presents some results from a comprehensive experimental program designed to determine the interaction between mechanical loading and corrosion of reinforcing steel, as well as their combined effect on serviceability and residual load- bearing capacity of reinforced concrete beams. Beam specimens with the size of 120mm×200mm×1700mm were subjected to four-point bending at various sustained loading levels (0%, 25%, 45%, and 65% of the ultimate load) during the corrosion test process. The marine tidal zone was simulated by alternating spraying and draining of 3.5% NaCl solution. An external direct current technique was used to accelerate the corrosion of the reinforcement. Residual flexural load-bearing capacity of the beams was evaluated at the end of the experiment. The results indicate that the loading has a significant effect on corrosion. Under simultaneous loading and accelerated corrosion conditions, the time-dependent deflection of the beams increases with the progressive corrosion of the reinforcement. The beams under high-level loading deteriorate more rapidly than those under low-level loading and without loading. As a result, the residual flexural capacity of the beams subjected to higher level loading was much lower than that of the beams subjected to lower level loading and in the absence of loading. The results suggest that, for a rational service-life prediction of reinforced concrete structures, the influence of the service load on the structural performance should be considered in combination with environmental conditions.

RESULTS RESULTING FROM AUTOFRETTAGE OF CYLINDER

Autofrettage is used to introduce advantageous residual stresses into wall of a cylinder and to even distributions of total stresses. Basic theory on autofrettage has been functioning for several decades. It is necessary to reveal profound relations between parameters in the theory. Therefore, based on the 3rd strength theory, σej/σγ, σej/σγ, σej/σγ, σej/σγ and their relations, as well as p/σγ, are studied under ideal conditions, where σej/σγ is equivalent stress of total stresses at elastoplastic juncture/yield strength, σej/σγ is equivalent stress of total stresses at inside surface/yield strength, σej′/σγ is equivalent stress of residual stresses at elastoplastic juncture/yield strength, σej′/σγ is equivalent stress of residual stresses at inside surface/yield strength, p/σγ is load-bearing capacity of an autofiettaged cylinder/yield strength. Theoretical study on the parameters results in noticeable results and laws. The main idea is： to satisfy ｜σej′｜=σγ the relation between kj and k is k^2ln kj^2 -k^2 -kj^2 ＋2=0, where k is outside/inside radius ratio of a cylinder, kj is ratio of elastoplastic juncture radius to inside radius of a cylinder; when the plastic region covers the whole wall of a cylinder, for compressive yield not to occur after removing autofiettage pressure, the ultimate k is k=-2.218 46, with k=-2.218 46, a cylinder＇s ultimate load-bearing capacity equals its entire yield pressure, or p/σγ =（k2 -1）/k2=lnk; when kj≤√e =1.648 72, no matter how great k is, compressive yield never occurs after removing Pas; the maximum and optimum load-bearing capacity of an autofrettaged cylinder is just two times the loading which an unautofrettaged cylinder can bear elastically, or p /σγ = （k2 - 1） / k2, thus the limit of the load-bearing capacity of an autofrettaged cylinder is also just 2 times that of an unautofrettaged cylinder.

Influence of cyclic loading on the fracture toughness and load bearing capacities of all-ceramic crowns

The purpose of this study was to investigate how cyclic loading influenced the fracture toughness of hot-press lithium disilicate and zirconia core materials and whether there was an increase in the propensity for crown failure. Two types of all-ceramic crowns including the IPS e.max Press system （n=24） and the Lava zirconia system （n=24）, were selected. Sectioned specimens were subjected to cyclic loading with the maximum magnitude of 200 N （R=0.1） until two million cycles. The material properties including Young＇s modulus （E） and hardness （H） and the fracture toughness （K,c） of the core materials were evaluated using indentation methods （n= 12 each）. The load-bearing capacities of the specimens were examined by means of monotonic load to fracture （n=12 each）. It was found that the material properties, including E, Hand Knc, of the two types of dental ceramics, were reduced. Statistical analysis indicated that there were no significant influences of fatigue loading on material properties E and H for both types of dental ceramics or Kgc for zirconia, while for the IPS e.max Press core, K,c, which was parallel to the direction of the lithium disilicate crystals, was significantly reduced （P-0.001）. A conclusion was drawn that zirconia possesses high mechanical reliability and sustainable capacity to resist fatigue loading, while fatigue loading remarkably degraded the anisotropic mechanical behaviour of hot-press lithium disilicate ceramics.

Analysis on Autofrettage of Cylinders

Autofrettage is an effective technique to improve load-bearing capacity and safety for pressure vessels.For autofrettaged cylinder,the depth of plastic zone,or overstrain is a key factor which affects load-bearing capacity and safety.The previous research on overstrain was not done in terms of the point of view of raising load-bearing capacity as far as possible and simultaneously avoiding compressive yield for cylinders experiencing autofrettage handling,and there were no analytic solutions of autofrettage in the above view point presented,the 3rd and 4th strength theories were not applied synthetically in the research to compare the results from these two theories.In this paper,with the aid of the analytic method,based on summing up the authors＇ previous research,results from autofrettage of a cylinder based on the 3rd and 4th strength theories are studied and compared,and the laws contained in the results are looked into.Then,the essential cause and reason for the obtained laws are analyzed and the inherent and meaning relations between various parameters in autofrettage theory are revealed.It is shown that the maximum radius ratio for equivalent residual stress at inside surface never exceeds the yield strength even for a cylinder experiencing wholly yielded autofrettage,or the critical radius ratio is kc=2.218 457 489 916 7…,irrespective of the 3rd or 4th strength theories.The equation relating the depth of plastic zone with the thickness of a cylinder is identical for the 3rd and 4th strength theories.In form,the optimum load-bearing capacity of an autofrettaged cylinder is two times the initial yield pressure of the unautofrettaged cylinder irrespective of the 3rd or 4th strength theory.The revealed inherent relations between various parameters and varying laws of the parameters as well as the forms of the relations under the 3rd and 4th strength theories not only have theoretical meanings but also have prospects in engineering application.

Design and Mechanical Characterization of an S-Based TPMS Hollow Isotropic Cellular Structure

Cellular structures are regarded as excellent candidates for lightweight-design,load-bearing,and energy-absorbing applications.In this paper,a novel S-based TPMS hollow isotropic cellular structure is proposed with both superior load-bearing and energy-absorbing performances.The hollow cellular structure is designed with Boolean operation based on the Fischer-Koch(S)implicit triply periodic minimal surfaces(TPMS)with different level parameters.The anisotropy and effective elasticity properties of cellular structures are evaluated with the numerical homogenization method.The finite element method is further conducted to analyze the static mechanical performance of hollow cellular structure considering the size effect.The compression experiments are finally carried out to reveal the compression properties and energy-absorption characteristics.Numerical results of the Zener ratio proved that the S-based hollow cellular structure tends to be isotropic,even better than the sheet-based Gyroid TPMS.Compared with the solid counterpart,the S-based hollow cellular structure has a higher elastic modulus,better load-bearing and energy absorption characteristics.

Lecablock, an Alternative Construction Material for the Exterior Walls of Passive House

In this paper it is attempted to investigate the Leca blocks as sustainable construction material for the exterior walls of passive house. The building physical properties of Leca design wall structure are studied along with the environmental impact and load-bearing capacity. To compare the results, a similar analysis is carried out considering the traditional wooden wall construction of passive houses. The results showed that Leca design wall structure can be an alternative sustainable solution to the traditional wooden wall structure of passive house, mainly due to its low U-value, its ability to handle moisture, and comparable structural load-bearing capacity. However, the wooden wall structure is more environmentally friendly than the Leca blocks due to its lower emissions to the environment and reduced energy use, especially during the manufacturing process.

OPTIMUM DESIGN OF HIGH-SPEED RAILWAY LOCOMOTIVE TRACTION GEAR

On the basis of deep investigation of locomotive traction gears manufactured at home and abroad , a variety of measures are putted forward to improve the driving load-bearing capacity and working life of our country's high-speed locomotive traction gears. The measures include the fol- lowing five aspects : optimally selecting the material and heat treatment process , optimally designing the tooth profile . reasonably choosing the manufacture accuracy and technique , optimally choosing the lubricant and the way of lubrication and seal , improving the dynamic feature of the gearing. In the respect of the tooth profile , a hob with optimal cutter angles is designed to make root thickness on the dangerous section as large as possible and the stress concentration as small as possible. Ad- dendum modification coefficient is optimized to minimize the maximum flash temperature in the course of meshing. Finally . finite element analysis method is used to calculate the deformation and the stress of teeth accurately. And on this basis , optimal profile correction and axial modification have been designed with regard to the start , continuious running and high speed travel of the loco- motive .

A novel inflatable rings supported design and buoyancy-weight balance deformation analysis of stratosphere airships

Owing to the unique advantages in flight altitude,dwelling time and wide coverage area,stratospheric airships provide permanent monitoring and surveillance for both civil and military applications.Here we propose a semi-rigid stratosphere airship design with circumferential high-pressure inflatable rings and a longitudinal carbon fiber skeleton supported inside.We perform numerical simulations to analyze the deformation characteristics during the whole ascending and descending process.An equivalent internal gradient pressure model of helium is established based on the capsule shape and buoyancy-weight equilibrium conditions.The implicit dynamic method is used to deal with the large deformation of the airship capsule under a low negative pressure condition.Deformation and load-bearing performance of the airship capsule,inflatable ring,skeleton,and suspension line are obtained under different working conditions.The results show that the airship,supported with the inflatable rings and the suspension lines,effectively maintains the shape and ensures the stiffness during the ascending,dwelling,and descending stages,especially suffering from negative pressure.

PREDICTIVE APPROACH TO FAILURE OF COMPOSITE LAMINATES WITH EQUIVALENT CONSTRAINT MODEL

This work established a new analytical model based upon the equivalent constraint model （ECM） to constitute an available predictive approach for analyzing the ultimate strength and simulating the stress/strain response of general symmetric laminates subjected to combined loading, by taking into account the effect of matrix cracking. The ECM was adopted to mainly predict the in-plane stiffness reduction of the damaged laminate. Basic consideration that progressive matrix cracking provokes a re-distribution of the stress fields on each lamina within laminates, which greatly deteriorates the stress distributed in the primary load-bearing lamina and leads to the final failure of the laminates, is introduced for the construction of the failure criterion. The effects of lamina properties, lay-up configurations and loading conditions on the behaviors of the laminates were examined in this paper. A comparison of numerical results obtained from the established model and other existed models and published experimental data was presented for different material systems. The theory predictions demonstrated great match with the experimental observations investigated in this study.

Residual Strength Study for Damaged Hull and Risk Analysis and Formal Safety Assessment

Residual strength assessment and prediction has been introduced in the project studies, including the determination of risk failure scenario, the change law of structural capacity and load effects in the damage of ship structure, the models for structural response and ultimate strength analysis, and dynamical model of reliability assessment. In addition, the project has improved the calculation method of ship ultimate load -bearing capacity, and studied the change law, assessment criteria of residual strength, and the method of predicting lifetime for aging ships. The valuable conclusions have been obtained by a large number of engineering calculations. The project and its extended results can provide theoretical foundation and background condition to make risk rule and modem design system, and can implement risk analysis and formal safety assessment for the marine world. The results will improve design quality and shipping safety of ship and offshore and enhanced their society and economic benefits.