Load-bearing Ability Research Articles

Stress–strain and burst failure analysis of fiber wound composite material high-pressure vessel

Composite material high-pressure storage vessel has been increasingly applied in the hydrogen storage industry. This study aims to establish parametric analysis of fiber wound composite vessel and investigate the stress distribution, failure mechanism as well as the burst strength. Based on the maximum strain criterion and Tsai-Wu failure criterion, the burst strength of the vessel and the failure mechanism of the cylinder segment were evaluated and studied. The stresses of the cylinder were much higher than those of the dome. The cylindrical part of the vessel is its weakest area. Matrix failure initiated at the spiral wound layer, then the accumulation of matrix failure resulted in the stiffness becoming degraded and hence fiber failure happened on the hoop wound layers. The fiber failure leaded to the ultimate failure of the vessel. The wound scheme of the outer layers also plays an important role on the load-bearing ability of the vessel. The burst strength of vessel with case-A wound was 122 MPa, while it was 91 MPa for case-B wound, about 25.4% decrease. The numerical results were compared with the burst mode studied in experiments on composite vessels and a good agreement was obtained. This study provides a theoretical foundation for safe design and utilization of composite material high-pressure vessel in the fields of hydrogen storage.

Stability of pinned-rotationally restrained arches

The article aims to find the buckling loads for pinned?rotationally restrained shallow circular arches in terms of the rotational end stiffness, geometry and material distribution. The loading is a concentrated vertical force placed at the crown. A geometrically nonlinear model is presented which relates not only the axial force but also the bending moment to the membrane strain. The nonlinear load-strain relationship is established between the strain and load parameters. This equation is then solved and evaluated analytically. It turns out that the stiffness of the end-restraint has, in general, a significant effect on the lowest buckling load. At the same time, some geometries are not affected by this. As the stiffness becomes zero, the arch is pinned-pinned and as the stiffness tends to infinity, the arch behaves as if it were pinned-fixed and has the best load-bearing abilities.

Two-Mode Controlled Single/Dual-Input DC–AC Inverter With Wide-Range DC Input

This article presents a two-mode controlled step-up inverter (TMCSI), which is capable of handling single or dual inputs with a wide range of dc input voltage. In comparison to traditional multistage dc/dc power conversion systems, the power conversion stage is reduced and the voltage/current stress of device is significantly alleviated without using high-voltage dc-bus capacitors. As a result, the reliability and overall conversion efficiency are improved accordingly. By combining the two working modes, the proposed inverter achieves uniform distribution of duty ratio under single/dual-input with a wide range of input voltage, and thereby is very suitable for systems having large input voltage variation. Moreover, based on the dual-input TMCSI, a novel power allocation method is also proposed to improve the system load-bearing ability. The power allocation method is controlled separately from two working modes that allows the two-input sources directly supply the ac load simultaneously. In this article, topology derivation, two-mode control strategy, characteristics of steady principle, and design criteria for the key circuit parameters are systematically analyzed, and important conclusions are obtained. Finally, the experimental results from the single/dual-input 500 VA 96-192 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> input and 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> /50 Hz output inverter prototype verify the effectiveness of the proposed TMCSI topology and its associated power regulation approach.

Finite element analysis of viscoelastic creep behaviors of deep-sea manned submersible viewport windows

This paper studies the creep and damage behaviors of PMMA deep-sea manned submersible viewport windows under constant seawater pressure. First, the viscoelastic creep experiments of PMMA material specimens under four groups of tensile stresses (near 30 MPa) are performed. Second, we adopt the three-element spring/dashpot viscoelastic model to study the creep behaviors of the PMMA viewport windows without considering damage behaviors. Third, we develop a viscoelastic creep/damage coupled model to evaluate the creep behaviors of viewport windows by leveraging the Burgers viscoelastic model with four spring/dashpot elements. The main features are represented by three aspects: 1. the creep initiation, growth and acceleration stages are included, 2. the introduced damage variable into the creep model is featured by the void volume fraction, which represents the degradation of load-bearing ability of viewport windows and 3. the creep/damage coupling behaviors are reflected by the increased functional relationship between the damage variable and the equivalent strain. Fourth, the finite element algorithm using ABAQUS-UMAT (user material subroutine) is developed to implement the three-element and four-element spring/dashpot models, and the unknown viscoelastic parameters are identified by combining with the tensile creep experiments on PMMA material specimens. Finally, finite element analysis is performed to evaluate the distributions of the creep strain, displacement and damage variable of viewport windows by discussing the effects of the water depth (100–500 m and 3000 m). As an extreme case, the creep lifetime of the conical viewport window under 3000 m water depth is also evaluated from the conservative perspective.

Load-bearing biodegradable PCL-PGA-beta TCP scaffolds for bone tissue regeneration.

A biocompatible and biodegradable scaffold with load-bearing ability is required to enhance the repair of bone defects by facilitating the attachment, and proliferation of cells, and vascularization during new bone formation. However, it is challenging to maintain the porosity and biodegradability, as well as mechanical properties (especially compressive strength), at the same time. Therefore, in the present work, a biodegradable composite structure of poly(caprolactone) (PCL) was designed using compression molding with varying amounts of poly(glycolic acid) (PGA) (25, 50, 75 wt%) and fixed amount (20 wt%) of beta tricalcium phosphate (beta TCP). It was hypothesized that the fabricated composite structure will develop porosity during the degradation of the PGA and that the corresponding decrease in mechanical properties will be compensated by new bone formation and ingrowth, in vivo. Accordingly, we have systematically studied the effects of sample composition on time-dependent dissolution and mechanical properties of the PGA/beta TCP scaffolds. The compressive strength increased up to ~92 MPa at 50% compression of the designed PCL-PGA samples. Furthermore, the dissolution rate, as well as weight loss, was observed to increase with an increase in the PGA amount in PCL. Based on the mechanical properties and dissolution data, it is concluded that the PCL-PGA scaffolds with beta TCP can be suitable candidates for bone tissue engineering applications, specifically for the reconstruction of bone defects, where strength and biodegradation are both important characteristics.

Surface characterization of steel/steel contact lubricated by PAO6 with novel black phosphorus nanocomposites

In the present work, two types of novel nano additives, titanium sulfonate ligand/black phosphorus (TiL4/BP) and titanium dioxide/black phosphorus (TiO2/BP) nanocomposites, were prepared. The tribological behavior of the steel/steel friction pairs lubricated by polyalphaolefins type 6 (PAO6) containing the nanocomposites under boundary lubrication was studied. The worn surfaces were analyzed using modern surface techniques. The experimental results show that the rubbed surfaces became smooth and showed little wear with the addition of the nanocomposites. TiO2/BP nanocomposites can significantly improve the lubricity of BP nanosheets under high contact stress. The synergistic roles of the load-bearing abilities and rolling effect of TiO2 nanoparticles, the slip induced by the BP with its layered structure, and the establishment of a tribofilm on the sliding interface are the basis of the tribological mechanisms.

Anti-sand erosion and tribological performance of thick DLC coatings deposited by the filtered cathodic vacuum arc

In order to improve the abrasion and erosion resistance in severe environments, 50-μm-thick diamond like carbon (DLC) films with a hardness of 27.3 GPa were fabricated using filtered cathodic vacuum arc technique coupled with a high-voltage pulse power. The microstructures, mechanical properties and tribological and anti-sand erosion performance of DLC coatings with different thicknesses were evaluated. The increase in thickness from 3 to 50 μm, resulting the adhesion of the coatings increased from HF1 to above HF1 level. Radial cracks or delamination were not observed at the edge of the indentation of 50-μm-thick coating. The coefficient of friction (COF) was decreased but wear rate was increased as coating growing thicker due to the stacking of graphited debris between the asperities. Mechanical polish was carried out on the 50-μm-thick films, which lead to the COF and wear rate decreased from 0.079 to 0.067 and 14.7 to 6.78 × 10−8 mm3/N·m at 20 N. The sand erosion test demonstrated that as the increase in thickness from 3 to 50 μm, average mass loss rate significantly decreased from 0.81 to 0.035 mg/g. High load-bearing capacity and ability to restrain the initiation and propagation of cracks were responsible for the great erosion resistance for thick coating.

Periprosthetic fractures of the acetabulum: revision endoprosthetics

Periprosthetic acetabular fractures are an increasing severe complication in revision arthroplasty. A differentiation is made between periprosthetic acetabular fractures (acute/traumatic fractures) and insufficiency fractures (chronic fractures). This article introduces anovel treatment algorithm that provides assistance in therapeutic decision making for implant selection and the anchoring philosophy based on diagnostic decision criteria and the relevant load-bearing osseous structures, taking the defect situation into account. The article provides an overview of original and review articles. The essential criteria for decisions in treatment planning are based on the stability of the primary cup, the load-bearing ability of the main anatomical structures and the resulting defect situation. For insufficiency fractures the reason for the revision and therefore the exclusion of periprosthetic joint infections (PJI) must additionally be considered. In the case of proven PJI a two-stage or multistage prosthesis exchange must be carried out. Based on the extent of apparent bony defects and pelvic discontinuity, the spectrum of treatment options ranges up to implantation of individual patient custom-made acetabular components. This overview introduces anew treatment algorithm that provides assistance in decision making for traumatic periprosthetic acetabular fractures and insufficiency fractures. It also provides decision criteria for selection of implants and the surgical approach. Due to the complexity of revision arthroplasty often requiring specialized expertise in trauma and orthopedic surgery and experienced revision surgeons, the operative treatment of periprosthetic acetabular fractures should only be carried out in specialized orthopedic and trauma surgery centers with appropriate experience.

Composite Hydrogel Model of Cartilage Predicts Its Load-Bearing Ability

Articular cartilage is a load-bearing tissue found in animal and human joints. It is a composite gel-like material in which a fibrous collagen network encapsulates large proteoglycan assemblies that imbibe fluid and “inflate” the network. Here we describe a composite hydrogel consisting of a cross-linked polyvinyl alcohol matrix filled with poly(acrylic acid) microparticles that mimics functional properties and biomechanical behavior of cartilage. The swelling and mechanical behaviors of this biomimetic model system are strikingly similar to that of human cartilage. The development of synthetic composite gel-based articular cartilage analog suggests new avenues to explore material properties, and their change in disease and degeneration, as well as novel strategies for developing composite tissue-engineered cartilage constructs for regenerative medicine applications.

Structural integrity analysis and damage assessment of a long composite wind turbine blade under extreme loading

The high demand of low cost wind energy needs to design large scale turbine blades with reduced weight which poses great challenges to their structural integrity while prone to extreme wind gusts. The loading can cause large-deflection bending and damage leading to significant drop in the load-bearing ability of long composite wind turbine (WT) blades. In this study, a comprehensive finite element (FE) modelling procedure is developed to simulate structural integrity and damage in composite blade using ANSYS software. The three-dimensional blade model is analyzed by carrying out geometrically nonlinear FE analysis to investigate the blade deformation and highly stressed regions leading to possible failure modes. The results show that the blade suction side is subjected to high compressive stress causing local skin buckling, which is further investigated using linear buckling analysis. Such local buckling drives interfacial debonding between skin and spar joined with a weak adhesive. Subsequently, the interfacial damage in the identified critical region is modelled by developing a damage submodel employing cohesive zone model (CZM) approach at the skin-spar interface. The analysis results indicate that buckling driven skin-spar debonding at adhesive interface is initial damage mode which can lead to progressive failure of the blade structure. Consequently, the ultimate load bearing capacity of WT blade is governed by a coupled buckling and debonding phenomenon even at load level below the ultimate design load. The simulation methodology adopted in this study can be employed to develop reliable and cost-effective computational tools for analyzing structural integrity and assessing damage in blade structure than expensive experimental testing.

Effect of Web Openings on Flexural Behaviour of Underground Metro Station RC Beams under Static and Cyclic Loading

This paper investigates the influence of multiple transverse web openings on the flexural behaviour of underground metro station reinforced concrete (RC) beams. This problem is outlined with an actual underground engineering project, in which the web opening used in the RC beams violates the current specifications. A total of five beams with different numbers of web openings are fabricated and tested under static and cyclic loading conditions, thereby simulating actual operations in unfavourable conditions. The results suggest that the existence of the openings decreases the loadbearing capacity, ductility, stiffness, and energy dissipation ability of the RC beams. Moreover, the results show that the corners of the openings are the weakest parts of the beams. However, additional reinforcements around the openings can partially mitigate the impact of the openings on the loadbearing and seismic performance of the RC beams. The laboratory experiments presented herein not only provide guidelines for the use of RC beams with web openings in actual engineering projects, especially underground projects where RC beams with web openings have seldom been investigated, but also shed light on improving the related design specifications.

Improving Bending Behaviour of Laminated Glass Using Novel Treatment Methods

Laminated glasses (LGs) are used frequently for load-bearing applications. The present work reports the newly developed ways to improve the load-bearing ability of LG. A three-point bending tests were conducted following the ASTM D790-03 before and after treatment. The load-bearing ability of treated LG sample was found superior to untreated LG. The fracture pattern of the treated LG was uniform in comparison to the untreated LG as impurities and defects were reduced during treatment. The mechanics of increased bending strength and modified fracture is also discussed with reference to the effects of thermo-chemical treatment of LG.

Why liquids can appear to solidify during squeeze-out – Even when they don’t

When liquids are squeezed out between two solid surfaces, they often exhibit layering, load-bearing ability, and a much increased viscosity. The combination of these phenomena is frequently interpreted as confinement-induced solidification. Here we propose that such behavior may often better be rationalized as the non-zero wavevector response of a pressurized liquid: bulk liquids contain structure even beyond the nanoscale as evidenced by their (damped) sinusoidal density correlations. Under confinement, this structure enables liquids to sustain non-isotropic stresses and thereby to carry load over a time span that is long enough for molecules to rearrange in the confined zone. In response to the load, viscosity can increase locally, in which case liquid flow is suppressed. This interpretation is supported by molecular-dynamics simulations of a key commercial base-oil component (1-decene trimer), which is squeezed out between a ridge and a substrate. The layering of the oil reflects the density correlations of the bulk liquid. At the same time, the confined liquid can sustain von Mises stresses exceeding locally 100 MPa over sufficiently long times for molecules to diffuse within the confined zone.

Strength retention, corrosion control and biocompatibility of Mg–Zn–Si/HA nanocomposites

Owing to the poor load-bearing ability and apparent cytotoxicity of polymeric and ceramic materials, magnesium-based materials can be an ideal substitute for bone repair applications. Magnesium is bioresorbable, unlike other metallic materials like titanium and stainless steel, has excellent biocompatibility, compressive strengths and elastic modulus similar to the natural bone, which circumvents the need for secondary surgery post-implantation in vivo. Against this background, in this study, magnesium-based nanocomposites were developed by using hydroxyapatite bioceramic as a nano reinforcement. Magnesium-based alloys were synthesized using selective alloying elements and hydroxyapatite incorporated nanocomposites were processed using the disintegrated melt deposition technique. The microstructure characterization revealed that the addition of hydroxyapatite resulted in superior grain refinement of the magnesium alloy matrix. The addition of hydroxyapatite improved the yield strength of the alloy matrix and displayed superior strength and ductility retention post corrosion for 21 days, under compression loading. The presence of hydroxyapatite improved the hydrophilicity of the alloy matrix thereby aiding the biocompatibility properties with improved corrosion resistance, level 0 cytotoxicity, and high cell attachment. Hence, the present study strongly suggests that magnesium alloy-based hydroxyapatite nanocomposites can be a suitable candidate for bone repair applications.

Implementation of a Reconfigurable Robot to Achieve Multimodal Locomotion Based on Three Rules of Configuration

SUMMARYIn this paper, we focus on the configuration design of a reconfigurable robot that merges the functions of wheels, tracks, and legs together. A deformable rim is utilized to make the robot wheel reconfigurable to change its locomotion mode. Three rules of configuration design to achieve reconfiguration between different modes are proposed: (1) in wheel mode, the track wheel set should be hidden inside the wheel rim; (2) in track/leg mode, the folded wheel rim should be hidden inside the caterpillar loop; (3) the circumference of the wheel rim in wheel mode should be equal to the length of the track ring in track mode. According to these rules, the configuration of the deformable rim, track wheel set, and telescopic spoke are analyzed and designed. A prototype of the reconfigurable wheel is fabricated by three-dimensional printing, and its functions of locomotion in different modes, the switch between different modes, and its load-bearing ability are tested, verifying the effectiveness of the configuration design. Furthermore, a prototype of the reconfigurable robot is manufactured by computerized numerical control (CNC) machining to verify the structural design of the reconfigurable wheel. Compared to traditional hybrid robots with separate wheels, tracks, and legs, this reconfigurable design lends the multimodal robot both excellent terrain adaptability and a compact structure; thus, it can be widely used as a universal mobile platform in search and rescue missions and explosive object disposal missions.

In Vivo Bone Effects of a Novel Bisphosphonate-EP4a Conjugate Drug (C3) for Reversing Osteoporotic Bone Loss in an Ovariectomized Rat Model.

ABSTRACTPathological bone loss is a regular feature of postmenopausal osteoporosis, and the microstructural changes along with the bone loss make the individual prone to getting hip, spine, and wrist fractures. We have developed a new conjugate drug named C3, which has a synthetic, stable EP4 agonist (EP4a) covalently linked to an inactive alendronate (ALN) that binds to bone and allows physiological remodeling. After losing bone for 12 weeks, seven groups of rats were treated for 8 weeks via tail‐vein injection. The groups were: C3 conjugate at low and high doses, vehicle‐treated ovariectomy (OVX) and sham, C1 (a similar conjugate, but with active ALN at high dose), inactive ALN alone, and a mixture of unconjugated ALN and EP4a to evaluate the conjugation effects. Bone turnover was determined by dynamic and static histomorphometry; μCT was employed to determine bone microarchitecture; and bone mechanical properties were evaluated via biomechanical testing. Treatment with C3 significantly increased trabecular bone volume and vertebral BMD versus OVX controls. There was also significant improvement in the vertebral load‐bearing abilities and stimulation of bone formation in femurs after C3 treatment. This preclinical research revealed that C3 resulted in significant anabolic effects on trabecular bone, and EP4a and ALN conjugation components are vital to conjugate anabolic efficacy. A combined therapy using an EP4 selective agonist anabolic agent linked to an inactive ALN is presented here that produces significant anabolic effects, allows bone remodeling, and has the potential for treating postmenopausal osteoporosis or other diseases where bone strengthening would be beneficial. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Ultrastructural response of tendon to excessive level or duration of tensile load supports that collagen fibrils are mechanically continuous

The basic collagen fibril structure of tendons continues to be debated in the literature. Some studies have proposed that collagen fibrils are longitudinally discontinuous, with the load-bearing ability of tendon dependent on interfibrillar shear strength. Other evidence indicates that collagen fibrils are probably structurally continuous, running uninterrupted from osteotendinous to myotendinous junction. In this study we explored the question of collagen fibril continuity in tendon by examining fibril response to tendon loading. Tendons were subjected to high stress and/or long duration tensile loading routines, after which we examined the ultrastructure of the tendons using differential scanning calorimetry and scanning electron microscopy, comparing the results from the loaded tendons to control samples taken from the same tendons prior to loading. Our results show that under ramp loading, collagen fibril damage begins near the end of the linear region in the stress-strain response (i.e., near the yield point). When tendons are allowed to gradually elongate under static load, tendon rupture is caused by failure of collagen fibrils, not uncontrolled slippage between fibrils. Our findings indicate that the collagen fibrils of tendon are at least sufficiently long to be mechanically continuous, meaning that tensile failure of tendon does not occur as the result of uncontrolled slippage between fibrils, but by failure of the fibrils themselves.

Direct link between mechanical stability in gels and percolation of isostatic particles.

Colloidal gels have unique mechanical and transport properties that stem from their bicontinuous nature, in which a colloidal network is intertwined with a viscous solvent, and have found numerous applications in foods, cosmetics, and construction materials and for medical applications, such as cartilage replacements. So far, our understanding of the process of colloidal gelation is limited to long-time dynamical effects, where gelation is viewed as a phase separation process interrupted by the glass transition. However, this purely out-of-equilibrium thermodynamic picture does not address the emergence of mechanical stability. With confocal microscopy experiments, we reveal that mechanical metastability is reached only after isotropic percolation of locally isostatic environments, establishing a direct link between the load-bearing ability of gels and the isostaticity condition. Our work suggests an operative description of gels based on mechanical equilibrium and isostaticity, providing the physical basis for the stability and rheology of these materials.

Self-aligned and hierarchically porous graphene-polyurethane foams for acoustic wave absorption

Manipulating the morphology of three-dimensional (3D) cellular structures in both macroscale and microscale is very important in designing a sound absorbing material effective in a broad frequency bandwidth. However, it is extremely difficult to synthesize the hierarchical porous structures having nano- and micro-pores in a self-assembled or controlled manner. Herein, we report an efficient strategy to fabricate the self-aligned and hierarchically porous graphene-polyurethane foams as a sound absorbing material via electrostatic repulsion mechanism of graphene oxide and potassium hydroxide activation. Two unique microscopic cellular structures are designed by controlling the morphology of graphene layers inside the polyurethane backbone using spontaneous self-alignment and stochastic disruptive methods, respectively. The obtained heterogeneous graphene microstructure network provides enhanced mechanically load-bearing ability and significantly improves the sound energy attenuation performance over 312% compared to pristine sound absorber depending on the existence of ordered or disordered graphene lattices, resulting in an efficient pathway for rapidly decaying out acoustic wave energy.

Novel evaluation method of acoustic emission data based on statistical fiber bundle cells

In general, the aim of acoustic emission-assisted tensile tests of composite materials is to identify and characterize the damage and failure modes of the specimens. This paper presents a fiber-bundle-cells-based statistical model, which provides a possible solution to the problem of characterizing the mechanical and failure behavior of the material. The model, based on the results of mechanical tests and acoustic emission measurements, decomposes the measured acoustic emission event number and tensile force–load time processes into components corresponding to the different damage modes. The acoustic emission events belonging to different failure modes are described by inhomogeneous Poisson point processes, while failures are modeled with the breakage of fibers as elementary parts of the sample. Hence, damage modes can be characterized with the number fraction, and the tensile strength and signal energy distributions of the components. Moreover, the variation of the number fraction of the intact or damaged fibers as a function of the load time can be calculated and depicted as well. As reliability function or a kind of damage map, it reveals the mechanical load-bearing ability of the material tested. The applicability of the model is demonstrated by compact tension testing and the comparison of short and long glass fiber-reinforced VERTON PP sheets and injection molded wood fiber-reinforced PP composites.