Slip Resistance Research Articles

Construction of biphasic FeCrAlWx high entropy alloys coating of BCC and Al-rich FCC second phase for dual enhancement of strength and plasticity

In this work, a series of novel FeCrAlWx (x = 0.25, 0.5, 0.75, 1) high entropy alloys (HEAs) coating were successfully prepared using laser cladding technology to simultaneously enhance both strength and plasticity. The effect of W on the microstructure, phase composition, strength, and plasticity of the coating was investigated. The results showed that the FeCrAlW0.75 HEAs coating, which exhibits a biphase structure consisting of a body-centered cubic (BCC) phase and a nanoscale Al-rich face-centered cubic (FCC) second phase, displays the most favorable overall performance. Specifically, FeCrAlW0.75 HEAs coating demonstrated a hardness, ultimate tensile strength, and ultimate elongation of 750.9 HV, 875.6 MPa, and 36.6 %, respectively, highlighting the simultaneous enhancement of strength and plasticity. The enhancement of strength in biphase FeCrAlW0.75 HEAs coating was attributed to the hardness of the BCC phase increased via added W, while the improvement in plasticity can be attributed to the twinning structure and low slip resistance of the nanoscale Al-rich FCC second phase. Furthermore, we analyzed the mechanism of W-improved strength by first-principles calculations, and investigated the formation mechanism of the nanoscale Al-rich FCC second phase for W-induced utilizing a pseudo-binary approach based on phase diagrams and elemental characteristics.

Influences of various parameters on shear stiffness of bolted joints subjected to shear load

Parameters which affect shear stiffness characteristics of bolted joints subjected to shear load should be elucidated in order to design mechanical structures for functionality focusing not only on their strength and self-loosening but also on their shear stiffness. In this study, we have both experimentally and analytically investigated the behaviors of a bolted joint subjected to shear load and primary parameters which determine the shear stiffness characteristics of bolted joints. The experiments have been conducted applying the shear load four times repeatedly on clamped plates of a bolt/nut assembly with washers. We measured the shear stiffness of bolted joints and the shear load at which the slippage started to occur between the clamped plates. Four types of washers were used in the experiments with different contact areas on the clamped plates in order to reveal the effect of contact area of washers. We also conducted FE analysis under the same conditions. As the results, it was seen that the shear stiffness slightly increased with an increase in the clamp force of bolted joint. The shear stiffness was not influenced by the number of loading cycles. It was also seen that the amount of rotational deformation in the bolted joint depended on the slippage between the clamped plates. Although the rotation deformation was very small until the slippage occurrence, the rotational deformation remarkably increased after the slippage occurred. In general, it is well-known that the joining portion of lap jointed plates by spot welding, for example, slightly and rotationally deformed, but it has never been elucidated that the inclination angle due to the rotational deformation depends on the slippage between the clamped plates in the bolted joint. It was also seen that the shear stiffness until the slippage occurrence increased with an increase in the contacting surface area between the clamped plates. Although we investigated the effect of surface roughness of the clamped plates only in the experiments, we cannot clearly reveal its effect on the shear stiffness. But it is seen from the FE analysis result that the friction coefficient between clamped plates had a slight influence on the shear stiffness. The result shows that the shear stiffness of bolted joint mainly depends not only on the slip resistance between the clamped plates but also on increase of the contact surface between the washers and clamped plates. The results can be applied in order to control the shear stiffness of lap-jointed plates by spot welding and so on.

Slip ratio of rigid wheels on TRI-1Lunar Simulant

Research work is conducted on performance evaluation of rover/rover wheel mobility in terms of slip ratio and motion resistance, which helps in solving and to overcome the present existing problems on a deformable soil terrain (flat/sloppy). The aim of this paper is to analyze the slip ratio and motion resistance of rigid wheels with various diameters, widths, lug height and different number of lugs, travelling on TRI-1 or Tiruchirappalli – 1 Lunar Soil Simulant. Slip ratio has more impact on the traveling performance of planetary rover which is a trafficability parameter. Hence, trafficability studies are required to understand –its affects, variation, and improvement of mobility from its parameter’s behavior. This paper brings out a best suitable combination of wheel that travels on TRI-1 Simulant, i.e., lugged wheels (small and large) with lug height 15 mm with 16 number of lugs and both wheels (plain small and plain large) are most suitable on Tiruchirappalli – 1 Lunar Soil Simulant with its maximum travelling performance and better mobility within the cases examined.

Effect of cellular structure on the mechanical properties of 316L stainless steel fabricated by EBF3

The cellular structure formed in additive manufactured 316L stainless steel (316L SS) plays a crucial role in achieving strength–ductility synergy. The cellular structure was also found in the 316L SS fabricated by electron beam freeform fabrication process (EBF3), and its microstructural characterization was analyzed. Interrupted tensile tests were carried out to demonstrate the effect of the cellular structure on the mechanical properties. The results showed that the microstructure of the as-deposited 316L SS consisted of the single austenite phase, and the enrichment of Cr and Mo elements was found in the cellular boundary. The orientation of the cellular structure and boundary was similar, and the obvious {100} preferred orientation was parallel to the building direction. The yield strength and fracture elongation of the as-deposited 316L SS parts were 316 MPa and 37.2%, respectively. Its ultimate tensile strength with a value of 632 MPa, was higher than that manufactured by conventional methods. The hardness and elastic modulus in the cellular interior were 2.88 ± 0.11 GPa and 227.45 ± 10.66 GPa, respectively. The cellular boundary had a higher hardness and a lower elastic modulus than the cellular interior. At the initial stage of tensile deformation, the cellular boundary deforms first due to its lower elastic modulus, causing the dislocation pileup and orientation change. The high dislocation density improved the slip resistance leading to the appearance of deformation twins after necking. The micron-dimples and nano-dimples formed in the fracture surface with the deformation of the cellular boundary and interior. Different from 316L SS fabricated by other additive manufacturing processes, the cellular structure improved the strain hardening capacity of the 316L SS fabricated by the EBF3 process.

Grip mechanisms and mechanical characterization of outsole materials: towards shoe slip resistance prediction

Grip mechanisms and mechanical characterization of outsole materials: towards shoe slip resistance prediction

Crystal plasticity-based analysis and modelling of grain size and strain path dependent micro-scaled deformation mechanisms of ultra-thin sheet metals

Multi-stage microforming is increasingly used in manufacturing of the miniaturized parts with complex structures and geometries. Optimization design of this type of manufacturing process, however, is still challenging due to its unknown intrinsic nature of the process. In the multi-stage deformation and microforming, the size effect (SE), the strain path change (SPC), and the intragranularly misoriented grain boundary (IMGB) generated in previous forming stage, are the main factors governing the deformation behaviors of ultra-thin sheets. To gain thorough insights into their influences on deformation and elucidate the associated micro-scaled mechanisms, SS 316L ultra-thin sheets with the thickness of 0.1 mm and different mean grain sizes (d¯) were used for two-stage tensile tests under the conditions with distinct pre-strain εpre and intersection angle θSPC (the angle between the previous loading direction and subsequent one). Mechanical tests reveal that increasing εpre and θSPC reduces the yield stress and hardening rate in SPC tension, but this reduction gets smaller after increasing d¯. This is because more IMGBs with complex pattern are formed in relatively large grains, raising the permanent deformation resistance inside grains in subsequent tension. To model the IMGB-induced hardening, the SPC-induced softening, and the SE-induced concurrent facilitations to the hardening and softening, an enhanced crystal plasticity constitutive relation was established. The physical essence that IMGB obstructs dislocation movement, is used to model the IMGB-induced hardening based on the interactions between the main slip planes and IMGBs. The hardening facilitation caused by increasing grain size is implicitly incorporated in determining the saturated slip resistance. Modelling of the SPC-induced softening is based on the high Schmid factor grain fraction and its influences are governed by pre-strain and the defined SPC parameter. The softening facilitation caused by coarsening grains is modelled in establishing the initial slip resistance in SPC deformation. The proposed simulation procedure and constitutive relationship help with accurately predicting the mechanical response and microstructure evolution in micro-scaled SPC deformation, and also provide a basis for modelling and design of the multi-stage microforming of complex miniaturized parts.

Dislocation patterning in the TiZrVTa refractory high-entropy alloy under tribological loading

Investigation of the plastic deformation mechanism of refractory high entropy alloys (RHEA) under tribological loading is crucial to understanding their excellent tribological properties. In this study, the dislocation patterning and the dependence of scratch system between the TiZrVTa RHEA and pure Ta under tribological loading were compared through nanoscratching molecular dynamics simulation, and partial experimental verification was conducted. The results showed that TiZrVTa RHEA exhibits a stable and excellent tribological response, stemming from the stable dislocation length evolution and firm dislocation patterning caused by the significant pinning effect of lattice distortion and chemical composition fluctuations on dislocations. In particular, both pure Ta and RHEA exhibit strong dependence of scratch system on their tribological properties and dislocation patterning. Compared to pure Ta, RHEA has better tribological properties in any scratch system, and dislocation patterning is more concentrated at the scratching trace. An accident is the widespread expansion of dislocation patterning in RHEA when scratching along the slip system ((110)[1–10]), indicating that more favorable stress conditions can overcome the strong dislocation slip resistance in RHEA, leading to severe plastic deformation. This study aims to better understand the deep roots of excellent theoretical tribological properties of RHEA through dislocation patterning analysis, thereby promoting the development of RHEA with better tribological properties.

A combined experimental and crystal plasticity study of grain size effects in magnesium alloys

This work presents a method to incorporate the micro Hall-Petch equation into the crystal plasticity finite element (CPFE) framework accounting for the microstructural features to understand the coupling between grain size, texture, and loading direction in magnesium alloys. The effect of grain size and texture is accounted for by modifying the slip resistances of individual basal and prismatic systems based on the micro Hall-Petch equation. The modification based on the micro Hall-Petch equation endows every slip system at each microstructural point with a slip system-level grain size and maximum compatibility factor, which are in turn used to modify the slip resistance. While the slip-system level grain size is a measure of the grain size, the maximum compatibility factor encodes the effect of the grain boundary on the slip system resistance modification and is computed based on the Luster-Morris factor. The model is calibrated using experimental stress-strain curves of Mg-4Al samples with three different grain sizes from which the Hall-Petch coefficients are extracted and compared with Hall-Petch coefficients predicted using original parameters from previous work. The predictability of the model is then evaluated for a Mg-4Al sample with different texture and three grain sizes subjected to loading in different directions. The calibrated parameters are then used for some parametric studies to investigate the variation of Hall-Petch slope for different degrees of simulated spread in basal texture, variation of Hall-Petch slope with loading direction relative to basal poles for a microstructure with strong basal texture, and variation of yield strength with change in grain morphology. The proposed approach to incorporate the micro Hall-Petch equation into the CPFE framework provides a foundation to quantitatively model more complicated scenarios of coupling between grain size, texture and loading direction in the plasticity of Mg alloys.

Numerical Simulations of the Driving Process of a Wheeled Machine Tire on a Snow-Covered Road

Wheeled machines, such as agricultural tractors, snowplows, and wheeled mobile robots, usually work on icy or snow-covered roads. Therefore, it is very important to study the driving and slip resistance of the tires of these machines. In this paper, we investigate the driving behavior of tires on snow-covered terrain by means of numerical simulations. A high-fidelity snow-covered road model is established, and smoothed particle hydrodynamics (SPH) and the finite element method (FEM) are employed to account for the behaviors of the snow layers and the pavement, respectively. We use the node-to-surface algorithm for the contact interactions between the snow and the pavement. The SPH parameters for the snow are calibrated by means of a triaxial compression experiment. A simplified tire model is established as well, using the FEM, and the effectiveness of the model is demonstrated via comparisons with the experimental data in terms of stiffness. Finally, the tire driving performance on the snow-covered road is simulated, and the influence of the tire surface configuration, external load, inflation pressure, and snowpack compression on the tire traction behaviors is systematically investigated.

Determination of the slip resistance of interspersed synthetic resin flooring with a convolutional neural network

The ramp slip test is a reliable and widely used method to evaluate the slip resistance of interspersed synthetic resin floors, common in industrial and parking areas. Following EN 16165 and using a ramp with varying inclinations, the floor R-class can be determined. This test can, however, only be performed in a laboratory, and not on-site. Here, we propose a method to determine the floor R-class from its surface topography, which can easily be measured on-site. In this study, floors of various slip resistances were prepared following the conventional method of spreading quartz sand onto a liquid resin. The interspersed surface creates a 3-dimensional topography, which is characteristic for the anti-slip properties. After the resin hardening, the R-class was measured and, in parallel, a convolutional neural network was developed and trained with the numerous photographs taken from the specimen surfaces. The used convolutional neural network classifies 95% of the surfaces into the correct R-class. This result makes it possible, for the first time, to determine the R-class slip resistance on-site with a high probability of correctness.

A novel method to predict slip resistance of winter footwear using a convolutional neural network

Slips and falls on ice are common causes of injury in the winter and can result in economic loss. Using slip resistant winter footwear is a key factor in reducing the risk of slips and eventually falls. In this study, we develop a model that classifies footwear outsoles based on how slip resistant they are on icy surfaces. Our dataset consisted of outsole images of 89 winter footwear samples that were previously tested and rated with a human-centred protocol called the Maximum Achievable Angle (MAA). We applied a transfer learning technique where the best classification model used the DenseNet169 pre-trained model and obtained an accuracy and F1-score of 0.93 ± 0.01 and 0.73 ± 0.03, respectively. Our results suggest that the proposed model was able to properly identify high and low slip resistance quality tread patterns. Our findings confirmed that a footwear’s tread pattern has a direct impact on its slip resistance. The proposed model will help footwear manufacturers to improve their workflow and increase product quality which can ultimately decrease the events of slips and falls.

Recycling of glass fibre reinforced polymer (GFRP) composite wastes in concrete: A critical review and cost benefit analysis

The application of fibre reinforced polymer (FRP) composites has increased substantially in recent years as a result of need for lighter and stronger materials. Currently, the reuse and/or recycling of composite wastes is very limited while most of wastes are disposed of in landfill or incinerated. Recently, mechanical recycling, fluidised bed, and pyrolysis has been developed to recycle FRP composites, but yet to be fully commercialised. As an alternative recycling strategy, incorporating glass fibre reinforced polymer (GFRP) into concrete has shown a great potential from both economic and environmental perspectives. This paper systematically reviews the performance of recycling of GFRP wastes into concrete with respect to fresh properties, mechanical properties, durability, environmental and financial aspects. Results show that the effect of recycled glass fibre reinforced polymer (rGFRP) on concrete mechanical strength is associated with the content of waste material (fibre or resin rich) and physical properties (shape, density, hydrophilicity) of GFRP recyclates, as well as the amount of recyclates. For rGFRP powder, the filler effect combined with the pozzolanic reaction can improve interfacial transition zone strength, increasing mechanical strength. Recycled glass fibre has reinforcing effect to restraint cracks and can provide extra slip resistance to strengthen the bond, resulting in improvement of flexural strength. Recycling of GFRP waste in concrete reduces water absorption of the concrete, improving durability properties. Furthermore, this research presents outcomes of cost-benefit analysis and benefit-cost ratio on five common GFRP recycling methods. The results show that repurposing rGFRP in concrete can reduce the total required investment and increase net profit. Recommendations and future perspectives are also provided to allow a wider adoption of rGFRP repurposing from industrial waste and the development of a more sustainable life cycle.

A robust phenomenological modeling framework based on cross-slip propensity factor for capturing the effect of dynamic strain aging on work hardening behavior of an Al-Mg alloy

In the present work, a new modeling framework for analyzing flow behavior of Al-Mg alloys is proposed by considering both direct and indirect effect of solutes on flow stress. While direct effect addresses the increased slip resistance due to dynamic strain aging (DSA), the indirect effect represents the role of solutes on cross-slip probability. This affects the dislocation annihilation propensity and consequently the work hardening behavior. The dislocation density evolution equation is suitably modified by including a factor based on activation volume and DSA-induced strengthening (σdsa) to account for the effect of solutes on dislocation annihilation propensity and develop a new phenomenological modeling framework for predicting flow curves spanning over a wide range of strain rate (0.00002–0.2 s−1). The proposed modeling framework is shown to be performing better than the existing models which consider only the direct effect of solutes on flow stress. Experimental validation of the proposed concept is shown via dislocation density measurements using X-ray line profile analysis, dislocation substructure analysis via transmission electron microscopy and fractography studies. The new modeling framework is also extended to predict flow curves of several Al-Mg alloys with varying Mg concentration to establish the robustness of the proposed concept.

부하의 변동에 따른 유도전동기의 자화 전력과 무효전력의 변화 분석

Induction motor is one of the representative inductive loads. Induction motors have coils in the stator and rotor respectively. This coil is distributed in the stator and the rotor, respectively, and has a resistive component and an inductive component according to the flow of current. The slip of an induction motor depends on the rotational speed. The slip of an induction motor varies according to no-load and changes in load. As this slip changes, resistance and reactance change. In an induction motor, the power required to form a magnetic flux is magnetizing power, and the power including the component used as a leakage component of the stator or rotor in the magnetizing power is called reactive power. The ratio of reactive power to active power in an induction motor is called power factor. In order to compensate the power factor, it is necessary to accurately know the magnitude of the magnetizing power required to form a magnetic flux. In order to know the magnitude of the magnetizing power, it is necessary to find the voltage at the air gap.

Assessment of Perceived and Measured Tribometer Readings in Evaluating Wet Barefoot Slip Resistance: A Gait-Based Approach

Assessment of Perceived and Measured Tribometer Readings in Evaluating Wet Barefoot Slip Resistance: A Gait-Based Approach

Pack Rust Mitigation Strategies for Flange Splice Connections in Steel Bridges

One of the main causes of infrastructure deterioration is corrosion. Different types of corrosion such as surface and pitting corrosion have been researched and addressed by industry. However, pack rust is another type of corrosion that requires attention because of its complexity and lack of research. Pack rust occurs between overlapping plates, which makes it difficult to remove and treat. A previous survey in the State of Indiana highlighted that a significant number of steel bridges exhibit some level of pack rust in the bottom flange of splice connections. Consequently, this study focuses on evaluating mitigation strategies that can delay further development of pack rust at the interface between the connected elements in a typical tension splice. Additionally, this study also examines the effects of pack rust on the tensile strength of a flange splice connection. The ultimate goal is to develop a series of guidelines that can be implemented in the field to address pack rust. To accomplish this, specimens were created to model the bottom splice connection. These specimens were exposed to a corrosive environment for different periods, and later tested under tension to evaluate any strength reduction. The level of pack rust developed in this study, which correlates to an exposure in the field of 20 to 40 years, increased the slip resistance of the specimens tested and did not decrease the ultimate strength. Finally, out of the three mitigation products tested, two had satisfactory results that merit further research and field testing.

On the strengthening and slip activity of Mg-3Al-1Zn alloy with pre-induced {101¯2} twins

{101¯2} twins were introduced into the magnesium (Mg) plate AZ31 via pre-rolling along its transverse direction. The plates, both with and without the pre-induced {101¯2} twins, were subjected to uniaxial tension along different directions. Using crystal plasticity modeling, we found that the strengthening effect of the pre-induced {101¯2} twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries, rather than the orientation hardening due to the twinning reorientation (although the latter did make its contribution in some specific loading directions). Besides, the pre-existing {101¯2} twins were found, by both experiments and simulation, to promote the activity of prismatic 〈a〉 and pyramidal 〈c + a〉 in the parent matrix of the material. Further analysis showed that the enhanced non-basal slip activity is related to the {101¯2} twin boundaries' low micro Hall-Petch slope ratios of non-basal slips to basal slip. With the critical resolved shear stress (CRSS) obtained from crystal plasticity modeling and the orientation data from EBSD, a probability-based slip transfer model was proposed. The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at {101¯2} twin boundaries than that at grain boundaries, which agrees with the experimental observation that the strain localization was primarily associated with the latter. The present findings are helpful scientifically, in deepening our understanding of how the pre-induced {101¯2} twins affect the strength and slip activity of Mg alloys, and technologically, in guiding the design of the pre-strain protocol of Mg alloys.

Safety of hospital floor coverings: A mixed method study

Adequate characteristics of floor coverings are essential for safely sustaining the movement of pedestrians on them. Coverings that are slippery when dry and/or wet can form a safety risk and cause people to slip and fall. Hospitals are public places where many people work in or visit. To comply with applicable standards, floor coverings in hospitals should have slip resistance characteristics that ensure the safety of pedestrians. This issue is not well researched keeping in mind that slipping and falling are the most reported work accidents in many countries. This study aims to investigate slipperiness of hospital floors in Türkiye and determine if they form a safety risk to pedestrians based on international standards. Coefficient of friction when dry and wet at multiple departments/wards in three hospitals in Türkiye were measured and statistically analysed using analysis of variance technique. It also aims to investigate potential hospital users’ opinion on floor slipperiness using a short questionnaire whose results were analysed using Mann-Whitney U test. Results show that floor coverings in hospitals form a safety risk to pedestrians when wet and that their friction do not comply with standards. Respondents to the questionnaire perceived hospital floors to be slippery, especially when wet, and said that those floor coverings should be made less slippery and safer. It is concluded that hospital floor coverings form a risk to pedestrians and that a change in their design is needed to ensure that their friction complies with safety standards and to safeguard their sustainable use.

Experimental investigation and design of slip resistant aluminium alloy–stainless​ steel connections

An experimental investigation into the structural response and slip resistance of aluminium alloy–stainless steel connections fastened by means of high-strength stainless steel swage-locking pins is presented herein. Thirty-seven friction tests on aluminium alloy–stainless steel shear connections featuring different surface treatments and material grades were carried out. Complementary material tests were also performed, while the roughness and hardness of the connected surfaces were measured. The failure modes, load–slip responses, friction coefficients and preloading behaviour of all specimens are fully reported, while the test setup, specimen dimensions, configurations of fasteners, and positions of displacement measurements, are explained. The slip factors corresponding to the different surface treatments are presented, while the key parameters affecting the preload losses of the swage-locking pins and the friction coefficients are described. Finally, the suitability of various surface treatments for aluminium alloy–stainless steel connections is evaluated, while design slip factors, as well as correction coefficients accounting for the influence of different material grades and preload levels on the response of the examined connections, are set out.

Development of high strength-ductility Mg-Er extruded alloys by micro-alloying with Mn

This work systematically investigated the influence of the micro-Mn addition on the microstructures and mechanical properties of Mg-Er alloys. To investigate their deformation mechanisms during tensile testing, electron back-scattered diffraction, transmission electron microscopy, slip trace analysis, and visco-plastic self-consistent polycrystal constitutive (VPSC) modeling were used. The study showed that the as-solid solution samples only consist of the α-Mg phase. All samples exhibit a complete dynamic recrystallized (DRXed) microstructure with an average grain size of 2.79 µm after hot extrusion. The ductility first increases from 26.02 % to 35.34 % and then remains unchanged with the increment of Mn content. Meanwhile, the yield strength significantly increases from 95 MPa to 200 MPa. According to VPSC results, the initial slip resistance (τ0) difference between prismatic and basal slips decreases from 109 MPa to 92 MPa and τ0 between pyramidal and basal slip systems from 129 MPa to 112 MPa. Both the VPSC and two-beam diffraction results confirmed that pyramidal<c+a>slip and<a>slip were activated during tensile deformation. The quantitative analysis of the slip trace line verified that the volume of non-basal slip reached 65 % when the content of Mn was increased to 0.9 wt%. Mn in solid solution increased the activity of pyramidal<c+a>and prismatic<a>dislocations during deformation, which is beneficial for accommodating c-axis strain. Consequently, the ambient ductility of Mg-2Er alloy with Mn addition is improved.