Load-carrying Ability Research Articles

Load Transfer Efficiency Based on Structural Deflection Assessment of the Precast Floating Track

In Korea, a precast floating track with anti-vibration isolators was recently developed to reduce the vibration and noise in urban railway stations, without disrupting train operations. This precast floating slab track is a newly developed structure and differs from existing conventional slab tracks. In this study, a Finite Element Method program (MIDAS CIVIL 2019) was used to analyze the load-carrying ability of structures under the train axle loads. After finishing the design, to understand more precisely about load transfer efficiency of this type of track, an assembly test (two load cases) was conducted with three precast panels (with rail 60 K mounted on) and compared with Finite Element Analysis results. The final results satisfied the test standards in Korea, which confirms that the precast floating track has an acceptable safety factor and structural behavior.

Anisotropy Effect of the Mechanical Metal Properties on the Assessment of the Load-Carrying Ability of the Launch Vehicle Oxidant Tank

The paper presents the results of the calculated estimate of the critical pressure level in the oxidant tank of the launch vehicle using generalized diagrams of elastic-plastic deformation of the aluminum alloy AMg6. These diagrams consider the anisotropy of the physical and mechanical properties of the material. The calculation of the stress-strain state is performed using the simplified calculation scheme for the specified structural element of the tank depending on the internal pressure in the axisymmetric statement considering the elastic-plastic deformations. The calculation analysis is based on the mixed scheme of the finite element method, which provides the continuous approximation of displacements and stresses. It allows one to determine the stress-strain state of the tank element with high accuracy. It is implied that the maximum values of stresses and strains occur in the area of the fillet region connecting the ring with the cylindrical shell of the tank. Complying with the obtained data, the calculation of the stress-strain state of the tank element using generalized deformation diagrams, taking into account the anisotropy of physical and mechanical properties and the nature of the load of aluminum alloy AMg6, leads to a more conservative estimate of the critical pressure level as compared with the standard calculation based on the uniaxial tensile diagram.

Analysis of open-hole-tension plates made of short fibre thermoplastic and reinforced with continuous fibre tailored inserts

In the present paper, the influence of tailored load introduction inserts applied to a bolt-loaded open-hole injection plate with different short glass fibre content is investigated. The tailored load introduction inserts made with a Tailored Fibre Placement (TFP) process, as well as open-hole injection plates without an insert were considered as reference samples. The samples were tested under tensile bolt-loading. The influence of the TFP-inserts on the load bearing properties of the open-hole injection plates was investigated. The test results show a huge increase of the load-carrying ability of the short-glass-fibre specimens when TFP-inserts are integrated. Moreover, the damage tolerance was dramatically improved as the specimens with integrated TFP-inserts did not fail abruptly and a residual strength higher than the strength of the test specimen without insert could be observed. However, the strength of the test specimen with integrated insert did not exceed the strength of the insert itself in most cases.

Methodology for Calculating the Technical State of a Reinforced-Concrete Fragment in a Building Influenced by High Temperature

The purpose of research was to develop a methodology for testing the fire-resistant quality of a building fragment influenced by a real fire to substantiate the main calculation methodology provisions and determine the residual load-carrying ability. While testing, it was supposed to determine the technical state of reinforced-concrete structures after high-temperature exposure and further intensive extinguishment. High-temperature heating and further fire extinguishing with water leads to the surface layers’ destruction and weakening of concrete. Impact on the structures of the open air leads to destruction and delamination of weakened concrete with further exposing of reinforcement and its corrosion. The approach, implemented in LIRA-SAPR software package, makes possible to take into account the influence of changes in the temperature regime of operation on the stress-strain state of the structure. After determining the temperature fields, it is necessary to reduce the rigidity characteristics of materials and perform a calculation of strength. When using this approach in order to determine the total deformations of the structure, it is necessary to take into account the creep deformation.

Tribological properties of hierarchical structure artificial joints with poly acrylic acid (AA) - poly acrylamide (AAm) hydrogel and Ti6Al4V substrate

Natural joints have the hierarchical structure of bone and cartilage, providing excellent lubrication and load-carrying capacity. In our research, the hierarchical structure artificial joints of Poly Acrylic Acid (PAA)- Poly Acrylamide (PAAm) hydrogel coating and Ti6Al4V substrate were formed using a simple yet versatile method by mimicking the hierarchical structure of natural joints. The efficient lubrication at friction interfaces was achieved. The composition and microstructure were confirmed by Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM). The hydrogel coatings were successfully prepared on the surface of Ti6Al4V substrate through the adsorption of the charged group. This hierarchical structure material exhibits the lower dynamic friction, approximately 0.085, which is much lower than bare Ti6Al4V, about 0.429. The wear on the surfaces after the tribological experiment is super-shallow and has no significant fracture area around the scratch. The PAA-PAAm hydrogel has a more uniform and compact cross-linked network porous structure, and the porous size is much smaller than PAA hydrogel. The cross-linked network porous structure is the main factor accounting for the low dynamic friction. This hierarchical structure of soft and hard improve the load-carrying ability and has the potential uses in artificial joints.

Combined effect of cylindricity, roundness and roughness on axial load-carrying ability of interference fits

Interference fits are commonly used in engineering for various applications. While the effect of many factors on the load-carrying ability of interference fits has been studied extensively, the combined effect of cylindricity, roundness and roughness does not appear to have been considered to that extent, and this paper is an attempt to remedy the situation. As a first step, finite element method was used to verify that there will be a reduction in the load-carrying ability due to the introduction of perfect geometrical deviations on the shaft. Thereafter, a detailed experimental investigation was carried out to study the effect of cylindricity and their joint effect with various other factors on the axial load-carrying ability of shaft–bearing interference fitted assemblies. A number of shafts of C40 steel of nominal diameter 20 mm were manufactured with varying cylindricity values and selectively assembled with standard deep grove ball bearings, thereby achieving interference fits with a grade of H7/u6 between them. The assembled specimens were tested on a Universal Testing Machine with a specially made fixture and the maximum extraction load determined. The effect of the various factors on the extraction load was examined using statistical methods. It was found that shaft cylindricity error did reduce the load-carrying ability of interference fits. The combination of interference, cylindricity and surface roughness was found to give the best prediction for extraction load. Certain other parameters were also examined, but they were not found significant.

Physiological Factors of Importance for Load Carriage in Experienced and Inexperienced Men and Women.

The ability to carry heavy loads is an important and necessary task during numerous outdoor activities and especially in military operations. The aim of this study was to investigate factors associated with load-carrying ability in men and women with and without extensive load-carrying experience. The energy expenditure during carrying no load, 20, 35, and 50kg at 2 walking speeds, 3 and 5kmh-1, was studied in 36 healthy participants, 19 men (30±6years, 82.5±7.0kg) and 17 women (29±6years, 66.1±8.9kg), experienced (>5years) in carrying heavy loads (n=16, 8 women) or with minor or no such experience (n=20, 9 women). A standard backpack filled with weights to according carry load was used during the walks. Anthropometric data, leg muscle strength, as well as trunk muscle endurance and muscle fiber distribution of the thigh, were also obtained. Extra Load Index (ELI)-the oxygen uptake (VO2) during total load over unloaded walking-was used as a proxy for load-carrying ability at 20, 35, and 50kg (ELI20, ELI35, and ELI50, respectively). In addition to analyzing factors of importance for the ELI values, we also conducted mediator analyses using sex and long-term carrying experience as causal variables for ELI as the outcome value. The study was approved by the Regional Ethics Committee in Stockholm, Sweden. For the lowest load (20kg), ELI20, was correlated with body mass but no other factors. Walking with 35 and 50kg load at 5kmh-1 body mass, body height, leg muscle strength, and absolute VO2max were correlated, while relative VO2max, trunk muscle endurance, and leg muscle fiber distribution were not correlated to ELI35 and ELI50.ELI50 at 5kmh-1 differed between the sexes. This difference was only mediated by the difference in body mass. Neither muscle fiber distribution, leg muscle strength, trunk muscle endurance, and body height nor did absolute or relative VO2max explain the difference.Participants with long-term experience of heavy load carrying had significant lower ELI20 and ELI50 values than those with minor or no experience, but none of the above studied factors could explain this difference. The study showed that body mass, without sex differences, and experience of carrying heavy loads are the dominant factors for the ability to carry heavy loads. Even though the effect of experience alludes to the need for extensive carrying training, no causality can be proven. Load carry training intervention studies is suggested for future investigations.

Повышение нагрузочной способности зубчатых муфт

Повышение нагрузочной способности зубчатых муфт

Comprehensive analysis of the strength and safety of potentially hazardous facilities subject to uncertainties

Aim. This paper aims to compare the two primary approaches to ensuring the structural strength and safety of potentially hazardous facilities, i.e. the deterministic approach that is based on ensuring standard values of a strength margin per primary limit state mechanisms, and the probabilistic approach, under which the strength condition criterion is the nonexceedance by the target values of probability of damage per various damage modes of the standard maximum allowable values. . The key problem of ensuring the structural strength is the high level of uncertainties that are conventionally subdivided into two types: (1) the uncertainties due to the natural variation of the parameters that define the load-carrying ability of a system and the load it is exposed to, and (2) the uncertainties due to the human factor (the limited nature of human knowledge of a system and possibility of human error at various stages of system operation). The methods of uncertainty mitigation depend on the approach applied to strength assurance: under the deterministic approach the random variables “load” and “carrying capacity” are replaced with deterministic values, i.e. their mathematical expectations, while the fulfillment of the strength conditions subject to uncertainties is ensured by introducing the condition that the relation of the mathematical expectation of the loadcarrying capacity and strength must exceed the standard value of strength margin that, in turn, must be greater than unity. As part of the probabilistic approach, the structural strength is assumed to be ensured if the estimated probability of damage per the given mechanism of limit state attainment does not exceed the standard value of the probability of damage.Conclusions. The two approaches (deterministic and probabilistic) can be deemed equivalent only in particular cases. The disadvantage of both is the limited capability to mitigate the uncertainties of the second type defined by the effects of the human factor, as well as the absence of a correct procedure of accounting for the severity of consequences caused by the attainment of the limit state. The above disadvantages can be overcome if risk-based methods are used in ensuring structural strength and safety. Such methods allow considering uncertainties of the second type and explicitly taking into consideration the criticality of consequences of facility destruction.

Effects of ballistic impact damage on mechanical behaviour of composite honeycomb sandwich panels

This paper presents the effects of ballistic impact damage on the mechanical behaviour of composite honeycomb sandwich panels. The panels are composed of facesheets made of carbon fibre reinforced laminates and the Nomex honeycomb core. Ballistic tests were conducted in a shooting range using live projectiles of three different calibres. The specimens were subjected to both normal and oblique impacts to simulate the damage to composite sandwich structures that can be inflicted by the use of small weapons or by fragments of anti-aircraft ammunition. The modes and extent of the damage induced have been analysed using optical microscopy, X-ray inspections and computer tomography methods. Structural performance of the intact and ballistically damaged panels has been investigated experimentally using in-plane compression tests, and numerically, based on the finite element modelling and analysis. The reduction in the load-carrying ability caused by the ballistic damage has been assessed for the panels under consideration and compared with that predicted by numerical simulations.

Experimental and analytical study of dynamic properties of UGM materials containing waste rubber

The permanent deformation characteristic is an important material property in determining the traffic-induced load-carrying ability of unbound granular materials (UGM). Since the repeated load triaxial test (RLT) is time-consuming, complicated, and expensive, it is highly desirable that a relatively simple and quick test can be used for estimating the permanent deformation of pavement materials in the base and subbase layers. In practice, the design engineers usually rely on California bearing ratio and unconfined compression strength tests which are static tests and very much less reliable and accurate compared to dynamic tests such as the Clegg impact hammer and dynamic lightweight cone penetrometer tests. No attempt had been previously made to correlate Clegg impact value and dynamic lightweight penetration index with the permanent deformation of construction and demolition (C&D) aggregates containing crumb rubber. On the other hand, information about the dynamic behaviour of construction and demolition (C&D) materials together with waste crumb rubber, as a green and environmentally friendly pavement material, is very limited. In the current research, a serial of RLT, the Clegg impact hammer tests, and the new dynamic lightweight cone penetrometer tests were performed to evaluate the strength and stiffness of UGM incorporating different sizes/percentages of crumb rubber. The main aim of this study was to develop a simple and reliable indirect approach for estimating the permanent deformation of UGM containing crumb rubber. Based on the experimental results, it was concluded that rubber could be blended with C&D aggregates for base/subbase applications. Also, according to the analytical results, CIV and DLPI could be considered as reliable and acceptable testing methods for estimating the permanent deformation of the unbound granular materials incorporating crumb rubber for the design of flexible pavement since there was a good correlation between the testing results and the phenomenological models.

Design and mechanical properties of hierarchical isogrid structures validated by 3D printing technique

Based on general lattice structure, a hierarchical isogrid (isotropic grid) structure with T-ribs was designed to enhance the buckling resistance and plastic performance, and manufactured by three-dimensional (3D) printing technique. It is proposed that under edgewise compression, the latticed panel has three structural failure modes, including material failure, global buckling and local buckling. Hierarchical topology simultaneously improves the out-of-plane and in-plane rigidity of the lattice ribs, as T-ribs balance the global bending rigidity and the local rib bending rigidity, endowing the panel higher buckling resistance. In the stage of post-failure plastic bending, the T-rib lattice shows good load-carrying ability and deforming ductility. Based on three failure modes, a multi-failure theory was built and verified by experiments and finite element method (FEM). A plastic model for the hierarchical isogrid panels was built to predict the post-failure deformation. The failure mode map method was proposed, providing reference for further optimal design.

Piston surface design to improve the lubrication performance of a swash plate pump

Abstract Mechanical power loss in hydraulic piston pumps comes from the friction between parts in relative motion, and wear is among the top pump failure mechanisms. Reducing friction and preventing wear require lubrication enhancement, which may be accomplished by proper surface texture design. Cylinder length is an important factor affecting the lubrication performance of the piston-cylinder system in a swash-plate pump. Our previous analyses revealed that under the same load, increasing the cylinder length could decrease the maximum pressure and increase the minimum film thickness, favorable for the pump operation with reduced wear; however, friction would become higher. The work reported in this paper intends to lower friction by textures in the piston surface while increasing, or at least maintaining, the load capacity of the piston system. Several textures are designed and their lubrication performances investigated, aiming at reducing the piston friction and improving the load-carrying ability of the system in a wide range of operation conditions. The effects of texture type, application location, and texture shape are studied, and their relationships with the friction and film thickness characteristics of the piston-cylinder interface are explored. Two optimal surface-texture designs are suggested, which are named the Step-Multiple-Grooves design and the Combine design.

Elastic hydrodynamic lubrication analysis for a sine movable tooth drive

The sine movable tooth drive has small radial dimension such that the heat, caused by friction, becomes an important factor in deciding its load-carrying ability. It is important to determine the amount of tooth lubrication in order to reduce the heat caused by the friction. This study provides equations for the meshing performance and provides the forces for the sine movable tooth drive. Using these equations, the minimum oil film thickness for the drive system is investigated. Results show that the minimum film thickness between the movable tooth and input shaft or shell changes periodically along the input shaft rotation angle. A large movable tooth radius and a movable tooth rotation radius could increase the film thickness between the movable tooth and the input shaft or the shell. In addition, a large speed ratio could increase the film thickness between the movable tooth and the input shaft, but this would also decrease the film thickness between the movable tooth and the shell. A large sine amplitude could increase the film thickness between the movable tooth and the input shaft, but this does not change the film thickness between the movable tooth and the shell. Under normal operation speeds, the hydrodynamic lubrication condition occurs between the movable tooth and the input shaft, and the partial membrane hydrodynamic state occurs between the movable tooth and the shell.

Mathematical Modeling and Analysis of Thermostressed State of Bimetallic Plate Under Electromagnetic Action in the Mode with Pulse Modulated Signal

Abstract The thermostressed state of a bimetallic plate under the electromagnetic action in the mode with pulse modulated signal (MPMS) at the resonant frequencies of the electromagnetic field is studied. There are established the critical values of the parameters of the electromagnetic action at which the bimetallic plate loses its load-carrying ability as a constituent element.

Tribological study of N-containing borate derivatives and their synergistic antioxidation effects with T531

Two N-containing borates, BTES and BMES, were synthesized with dodecyl phenol, 2-(N-containing heterocyclic) ethan-1-ol, boric acid, and dibutylamine, and their tribological properties in rapeseed oil (RSO) were investigated using a four-ball tester. The results showed that the load-carrying ability (PB value) of RSO can be improved by 40.9% and 67.9%, respectively, when using 0.5 wt% BTES and BMES. Moreover, the antiwear and friction-reducing performances of the additive-containing oils increased with the additive concentration. The X-ray photoelectron spectroscopy results of the worn steel ball surfaces showed that BTES and BMES formed protective films, which contained boron oxide, iron oxide, ferrous sulfate, ferrous sulfide (for BMES), and other organic nitrogen compounds, on the metal surfaces. The better load-carrying and antiwear performances of BMES than those of BTES might be due to their different sulfur contents, which result in different tribochemical reaction films on the contact surfaces. The oxidation stability tests showed that BTES and BMES possessed synergistic antioxidation activity with N-phenyl-α-naphthylamine (T531), and consequently, the oxidation activation energy of the oil sample increased by 77.85% and 82.19%, respectively, compared with that of RSO when the oil sample contained 0.05 wt% BTES/BMES and 0.25% T531.

Predicting damage accumulation and fatigue life of UD composites under longitudinal tension

Unidirectional composites under cyclic longitudinal tension develop damage through the accumulation and clustering of fibre–breaks, and through fibre–matrix interface debonding growth; these processes lead to a reduction of the material’s load–carrying ability with increasing loading cycles, which raises a challenge to predict the fatigue response of composite structures. This paper proposes the first model in the literature to predict the kinetics of fibre–breakage and their effect on the macroscopic response of unidirectional composites under cyclic longitudinal tension. The model couples (i) a statistical hierarchical scaling law to predict fibre failure with (ii) a Paris law to predict interfacial fatigue damage propagating from broken fibres; due to its analytical formulation, the model predicts the response of composite bundles up to virtually any size and for their entire fatigue life in less than one minute. Model predictions for the accumulation and clustering of fibre–breaks show a good correlation with experiments from the literature; the model also predicts that, although the critical cluster size does not vary significantly between static, low–cycle/high–stress fatigue, and high–cycle/low–stress fatigue, the material can withstand the highest amount of softening under high–cycle/low–stress fatigue.

Crashworthiness optimization of automotive parts with tailor rolled blank

Tailor rolled blank (TRB) as an advanced manufacturing process developed recently has broad application prospects in automotive and aerospace industries for its significant advantages in better load-carrying ability and lighter mass. TRB is a typical custom product, whose performance is closely related to its thickness variation, thus how to obtain the optimal thickness variation of a TRB part becomes a challenging task, especially for crashworthiness design. To address this issue, an optimization method based on the variation of wall thickness is presented to maximize the energy absorption capacity of TRB parts. Firstly, finite element (FE) models of two typical automotive parts, TRB top-hat column and TRB bumper beam, are established and validated through crushing experiments. Then a heuristic optimization method is proposed based on the general assumption that more mass enables to absorb more energy. The elemental energy density is used to optimize structural thickness distribution of geometrical and material nonlinear structures. Numerical results demonstrate the capability and effectiveness of the proposed optimization method for achieving the best thickness layout of automotive TRB parts for crashworthiness.

Influence of prestressing the textile on the tensile behaviour of textile reinforced concrete

In textile reinforced concrete (TRC), the yarns of the textiles are inherently wavy due to the manufacturing process. In most structural applications, this leads to delayed activation of textiles during loading and affects the composite performance negatively. In this context, the paper reports on the significance of mechanically prestressing or stretching the textiles before casting the TRC towards enhancing its load-carrying ability, which has been assessed by comparing the responses of specimens with textiles placed by manual and mechanical stretching. Studies were carried out to determine the uniaxial tensile behaviour of TRC with two types of alkali-resistant glass textiles, woven and bonded and their combinations. TRC with mechanically-stretched woven textile exhibits better performance compared to that of the manually stretched textile, in terms of load-carrying ability though the elongation at failure could be compromised for specimens with bonded textiles. Mechanically stretched textile lead to pronounced strain hardening behaviour, enhancement in the stress at first cracking and stress at peak, which also increase as the number of layers increases. The failure of TRC with manually stretched textile occurs with the pullout of the textile from the matrix contrasting with the rupture of textile when mechanically stretched. X-ray tomography images of the internal structure of TRC further revealed that there is less frictional bond loss and debonding of textile from the matrix for mechanically stretched textile.

Antiwear performance of ionic liquid+graphene dispersions with anomalous viscosity-temperature behavior

Abstract New dispersions of few-layers graphene (G) in 1-ethyl-3-methylimidazolium ([EMIM]) ionic liquids (ILs) with dicyanamide ([DCA]) or bis(trifluoromethylsulfonyl)imide ([TFSI]) anions have been obtained by mechanical mixing and sonication. IL+0.5 wt% G dispersions show constant viscosity values from 357K (for IL = [EMIM][DCA]) or from 385K (for IL = [EMIM][TFSI]) to 393K. IL + G dispersions with G > 0.5 wt% show linear viscosity increases with increasing temperature, from 306K (for [EMIM][DCA]+1 wt%G) and from 330K to 393K (for [EMIM][TFSI]+0.75 wt%G and [EMIM][TFSI]+1 wt%G). Addition of graphene improves the poor wear reducing performance of [EMIM][DCA], and prevents surface damage on steel when added to [EMIM][TFSI]. Graphene increases the load-carrying ability of ILs, forms a surface layer on the sliding path and retains wear debris, preventing the formation of large abrasive particles.