Normal Load Research Articles

New Equipment for Determining Friction Parameters in External Conditions: Measurements for the Design

Friction parameters such as the angle of internal friction and the external friction of soils (bulk materials) show the possibilities of further material use. These are, for example, possibilities for soil processing, handling, and storage. The determination of friction parameters is usually carried out under laboratory conditions. For the possibility of determining the properties of soils outside the laboratory in terms of immediate material response, a laboratory prototype was developed. The main objective for its development was to determine the effect of the shape of the friction surface when “sliding” on the soil. This was achieved with the help of validation equipment designed to measure, test, and validate the processes of raking, material piling, material transfer and removal, and tool movement or sliding on or in a material. It was found that by using an appropriate speed and normal load, the Jenike method can be applied to determine the angle of external friction over a shorter distance with an error of about 6–7.5% from the values measured on a calibrated shear machine. The results also showed that the method can be applied to detect the shear stresses that arise when a tool is plunged into a material, and thus predict the possible increase in energy loss during the process.

Association Between Age and Cognitive Severity in Participants from the Longitudinal Early‐Onset Alzheimer’s Disease Study

AbstractBackgroundAge‐related cognitive declines are well‐documented in cognitively normal adults (van der Willik et al., 2021), as are greater cognitive impairments with advancing age in traditional‐ (or “late‐”) onset Alzheimer’s disease (LOAD; Davis et al., 2018). Early‐onset Alzheimer’s disease (EOAD; diagnosis ≤65 years old) possesses a unique disease course and underlying pathology relative to LOAD (Mendez, 2012), consequently it is unknown if the association between age and cognitive severity is similar. The objective of the current study is to examine the relationship between cognition and age‐at‐baseline in participants enrolled in the Longitudinal Early‐Onset Alzheimer’s Disease Study (LEADS; Apostolova et al., 2019).MethodCross‐sectional cognitive data from 371 participants (aged 40‐64) enrolled in the LEADS protocol were analyzed, using composites for the domains of Episodic Memory, Speed/Attention, Visuospatial skills, Language, and Executive skills. Relationships between age‐at‐baseline and cognition were examined using linear regression based on diagnostic group classification (cognitively normal [CN], amyloid‐positive EOAD, and amyloid‐negative Early‐Onset non‐Alzheimer’s disease [EOnonAD]), controlling for the effects of age and education years.ResultDemographic characteristics for each group are shown in Table 1. Across cognitive domains, the CN group displayed either non‐significant or negative relationships (Executive skills; r = ‐0.30, p = .006) between age‐at‐baseline and cognitive performance (Figure 1 and Table 2). Conversely, the EOAD group showed consistent positive relationships for domains of Speed/Attention (r = 0.23, p<.001), Visuospatial Skills (r = 0.19, p = .01), and Episodic Memory (r = 0.16, p = .02). A similar non‐significant trend was observed for the EOnonAD group for Speed/Attention (r = 0.17, p = .19). When considering those with amnestic‐variant early‐onset dementia across diagnostic groups, positive relationships between age‐at‐baseline and cognition were observed for Speed/Attention (r = 0.19, p = .006) and Visuospatial skills (non‐significant trend; r = 0.14, p = .05), but not for Episodic Memory (r = ‐0.06, p = .35).ConclusionWorse cognitive severity was associated with younger age‐at‐baseline for EOAD participants in LEADS. Similar trends were observed for EOnonAD participants, though to a lesser magnitude. These results were counter to those observed for CN participants, and to what is known about cognitive trajectories in normal aging or LOAD. These findings further support previous suggestions that EOAD appears to be a distinct entity relative to LOAD.

Numerical simulation of the rheology of alumina abrasive particles applied to UHMWPE during the microabrasion test

The material used for 50 years in orthopedics for joint replacements is ultra-high molecular weight polyethylene (UHMWPE). Joint replacements are designed so that the metal is in surface contact with the polymeric material, and it is used in most degenerative joint disorders. A problem with joint replacements is the half-life of their UHMWPE components resulting from surface contact, leading to premature wear. This leads to the detachment of wear particles causing osteolysis. In the present investigation, a numerical simulation of the rheology of 5 μm size alumina abrasive particles applied to UHMWPE type GUR 1020 was performed by duplicating the microabrasion test. An analogy was proposed between the alumina particles observed in the scanning electron microscope (SEM) and the gravel stone obtaining a geometry similar to that of the alumina particles. A 3D scanner was used, obtaining different randomly selected gravel models. They were scanned and rendered to obtain the IGS files to be used in the finite element software. Using Archad’s abrasive wear theory, the volume displaced by the abrasive particles was obtained as a function of the geometry of the abrasive grains, influenced by the entry position of one or more of the different cutting edges contained in the geometry, the hardness of the softer material, the value of the normal load and the sliding distance. Individual trace profiles were obtained by 2D profilometry and wear traces were analyzed by SEM. Explicit dynamic analysis of particle motion was used to simulate the entry, transition and displacement during the abrasive wear test caused by detached particles. The experimental results of the microabrasion test were compared with finite element analysis, demonstrating that simulation can be used as a reliable tool to obtain information about the type of wear of a material.

A multifunctional shear apparatus for rocks subjected to true triaxial stress and high temperature in real-time

Deep engineering disasters, such as rockbursts and collapses, are more related to the shear slip of rock joints. A novel multifunctional device was developed to study the shear failure mechanism in rocks. Using this device, the complete shear–deformation process and long-term shear creep tests could be performed on rocks under constant normal stiffness (CNS) or constant normal loading (CNL) conditions in real-time at high temperature and true-triaxial stress. During the research and development process, five key technologies were successfully broken through: (1) the ability to perform true-triaxial compression–shear loading tests on rock samples with high stiffness; (2) a shear box with ultra-low friction throughout the entire stress space of the rock sample during loading; (3) a control system capable of maintaining high stress for a long time and responding rapidly to the brittle fracture of a rock sample as well; (4) a refined ability to measure the volumetric deformation of rock samples subjected to true triaxial shearing; and (5) a heating system capable of maintaining uniform heating of the rock sample over a long time. By developing these technologies, loading under high true triaxial stress conditions was realized. The apparatus has a maximum normal stiffness of 1000 GPa/m and a maximum operating temperature of 300 °C. The differences in the surface temperature of the sample are constant to within ±5 °C. Five types of true triaxial shear tests were conducted on homogeneous sandstone to verify that the apparatus has good performance and reliability. The results show that temperature, lateral stress, normal stress and time influence the shear deformation, failure mode and strength of the sandstone. The novel apparatus can be reliably used to conduct true-triaxial shear tests on rocks subjected to high temperatures and stress.

A Fractal Prediction Method for Contact Stiffness of Helical Gear Considering Asperity Lateral Contact and Interaction

The normal contact stiffness (NCS) on rough surfaces has a significant impact on the dynamic characteristics of helical gear. Aiming at the problem of inaccurate calculation of the NCS model under the traditional Hertz theory of smooth surfaces, a fractal prediction model of helical gear contact stiffness considering asperity lateral contact and interaction between asperities is proposed in this paper. The variation formula of asperity and the correction coefficient of a tooth contact surface under asperity lateral contact and interaction are derived, and the influence of micro-elements on normal load and NCS is qualitatively analyzed. The results show that the NCS of considering the interaction and lateral contact of asperity is closer to the experimental results; the contact surface correction coefficient increases with the increase of curvature radius and load. The NCS of a tooth surface increases with the increase in fractal dimension D or the decrease in roughness amplitude G. The influence of asperity lateral contact and interaction decreases with the increase in D and the decrease in G. The NCS of the helical gear decreases under the lateral contact and interaction of the asperity, which is critical for exact estimation of the NCS of contact surfaces in gear.

Modelling the thermo-mechanical behaviour of a rock joint

The CNSC, the Canadian regulator for the nuclear industry, participated in DECOVALEX-2023 Task G that focuses on the thermo (T) - hydro (H)- mechanical (M) behaviour of rock joints. Joints are omnipresent in rock masses and are planes of weakness in the host rock. When deep geological repositories (DGRs) for radioactive waste are being considered in areas where rock joints are present, the joints could be preferential pathways for radionuclide migration. Therefore, their THM behaviour must be better understood to assess the safety of the DGR. Under different possible internal and external perturbations, a joint can move by shear and dilation. If the joint crosses the emplacement area of a waste container, the heat generated from the waste can itself induce shearing of the joint. Excessive shear movement can in turn lead to failure of the container, resulting in earlier release of radionuclides. Furthermore, dilation that might accompany shear, results in an increase in the joint aperture creating a faster flow path for radionuclide transport. Mathematical models are important tools that need to be developed and employed, in order to assess joint shear and dilation under different loading conditions, such as the heat generated from the emplaced waste. The authors have developed such a mathematical model based on a macroscopic formulation within the framework of elasto-plasticity. It is verified against analytical solutions and validated against shear under constant normal load tests and thermal shearing tests of joints in granite.

Evaluation of the behavior of the interface zone between an asphalt mixture and an inductive power transfer pad

Wireless charging of Electric Vehicles (EVs) is seen as part of an important strategy to reduce emissions from essential transportation trips of people and goods. Resonant Inductive Power Transfer (IPT) is used in the development of wireless charging systems for in-road charging systems. IPT pads are embedded in a pavement infrastructure to create a magnetic field that is coupled into a similar pad fitted underneath an EV. This is then converted to the voltage and current needed to charge the onboard battery. This method enables EVs to wirelessly receive a charge while stationary or in motion. However, ensuring the robustness of this integrated in-road system is essential. Poor interface bonding between a surrounding asphalt mixture and an IPT pad decreases the structural integrity within the IPT pad-asphalt pavement system, hence increasing the risk of damage to the system. The purpose of this study is to investigate the behavior of an IPT pad-asphalt interface zone by performing direct shear tests. In the experimental setup, a normal compressive load is applied to a three-layer cylindrical specimen, comprising an asphalt mixture, the interface material, and the material forming the outer containment layer of the pad. The influence of temperature, moisture, and normal stress on the interface shear strength is investigated. Among the three interface materials tested (epoxy bitumen, epoxy resin, and structural plastic adhesive), the epoxy resin material showed the highest shear strength at 25 °C. The interface shear strength and the shear stiffness decreased for all three materials with increasing temperature, with the epoxy bitumen material being the most temperature sensitive, yielding a decrease in strength of 77 % and stiffness of 62 % between 15 °C and 40 °C. Experiments were performed using an orthogonal test design. Five variables, known to affect the interface shear strength, each variable assuming three values, were considered. The results of a range analysis and analysis of variance (ANOVA) showed that temperature has the most significant effect on the shear strength of the interface zone, i.e. between the asphalt mixture and pad surfacing. Other important factors affecting the shear strength are the interface material and the shear deformation rate. A numerical study of a full-scale IPT-asphalt pavement system is presented to show the effect of the interface bonding condition on the longitudinal and transverse strains at the bottom of the asphalt layer and the fatigue life. The results of this study will be used in the design of an IPT pad-asphalt pavement system by minimizing the differential permanent displacements between an IPT pad and the surrounding asphalt pavement.

Determination of the stress-deformed state of the grinding circle adjustment pencil

Using the Ery stress function in a linear formulation, using the methods of the classical theory of elasticity, an algorithm for analytically determining the stress-strain state of the working part of the abrasive wheel straightening tool as a two-layer composite material was developed. The algorithm allows considering arbitrarily distributed normal and tangential loads of the working surface of the abrasive grain of the tool. It considers the mandrel's limitation of deformations of the grain and the material that attaches it to it, the compatibility of the deformation of the grain and the material of its attachment to the mandrel, and their mechanical properties.
 Calculations performed according to the obtained algorithm allowed the following to be established. The maximum standard stresses on the working face of the grain exceed the corresponding stresses on the opposite face due to their more uniform distribution. The tangential stresses are almost uniformly distributed along the specified face. The material connecting the grain to the tool mandrel deforms almost uniformly due to its lower modulus of elasticity and smaller thickness than the abrasive grain's modulus of elasticity and thickness. Determining the stress-deformed state of the executive part of the pencil for correcting the working surfaces of grinding wheels for abrasive processing of materials makes it possible to specify the known mechanism of their interaction and increase the efficiency of the technological process of restoring the working surfaces of the tool for abrasive processing of metals.
 Taking into account the simultaneous deformation of the abrasive grain and the material that attaches it to the pencil mandrel, determining their stress-strain states using the methods of the classical theory of elasticity allows us to consider the results obtained by the given algorithm as sufficiently reliable within the limits of linear deformation. It is advisable to direct further research to determine the durability of the "abrasive grain-bond" system under variable cyclic loads.

Experimental and Numerical Investigations on the Dynamic Response of Blades with Dual Friction Dampers

Friction dampers are widely employed to reduce blade resonance vibration amplitude in turbomachinery. In this paper, a study was performed on the forced response of two blades with dual friction dampers. Numerical simulation and experimental testing were conducted. Firstly, the dynamics of the blade and dual friction damper system assembly are modeled. A nonlinear code based on the multi-harmonic balance method was developed to calculate the resonance response. In this analysis, both the blade and the damper are modeled with the finite element and the matrices reduced with the component mode synthesis method, while the contact forces are modeled with a one-dimensional variable normal load array element. Secondly, a test rig made of two blades and dual friction dampers, the material of which was steel, was established to measure the nonlinear frequency response function curves of the blade system. The results indicate that when a dual friction damper is applied, superior vibration reduction characteristics are demonstrated, with the system exhibiting an average 21% reduction in the response amplitude levels and an increase of 3% in the frequency shifting range compared to a single damper. Dampers positioned at relatively higher locations contribute significantly to the vibration reduction process. In the end, the numerical predictions match very well with the experimental ones.

Numerical study on influence of particle shape and deformation on friction behavior of flexible cylindrical particle flows

AbstractA discrete element method (DEM) model for deformable particles is established and adopted to investigate the Jenike shear process of flexible cylindrical particles with different aspect ratios (4 < < 6). The DEM model is firstly validated against both experimental data and analytic solutions. Then, numerical simulations are carried out and the effects of particles shape and deformation on their friction behavior are investigated through a particle‐scale analysis on particle deformation, coordinate number, contact forces, orientation and internal friction angle. Comparative results between flexible and rigid particles under the same conditions show that the shear stress increases almost linearly with the normal load regardless of particle stiffness or shape. For both rigid and flexible particles, the shear stress and internal friction angle increase with . The shear stress and internal friction angle of the flexible particles are higher than those of the rigid ones especially when = 6. The latter has more inter‐particle contacts but the former has stronger contact forces. When = 4 and 5, the flexible particles without many initial deformations will deform significantly during the shear process with a complex reconfiguration taking place. However, when = 6, the initial deformation and internal forces of the flexible particles only change slightly during the shear process. It is thus believed that the high shear stress and internal friction angle of the flexible particles with = 6 are caused by their solid packing structure which strongly enhances the capability of the particle flow to resist shear. The current knowledge will be helpful for improving the kinetic theories for granular flow for complex irregular particle flows.

Mechanical behaviors of backfill-rock composites: Physical shear test and back-analysis

The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence. For exposing the shear failure mechanism of backfill-rock composites, we conducted shear tests on backfill-rock composites under three constant normal loads, compared with the unfilled rock. To investigate the macro- and meso-failure characteristics of the samples in the shear tests, the cracking behavior of samples was recorded by a high-speed camera and acoustic emission monitoring. In parallel with the experimental test, the numerical models of backfill-rock composites and unfilled rock were established using the discrete element method to analyze the continuous-discontinuous shearing process. Based on the damage mechanics and statistics, a novel shear constitutive model was proposed to describe mechanical behavior. The results show that backfill-rock composites had a special bimodal phenomenon of shearing load-deformation curve, i.e. the first shearing peak corresponded to rock break and the second shearing peak induced by the broken of aeolian sand-cement/fly ash paste backfill. Moreover, the shearing characteristic curves of the backfill-rock composites could be roughly divided into four stages, i.e. the shear failure of the specimens experienced: stage I: stress concentration; stage II: crack propagation; stage III: crack coalescence; stage IV: shearing friction. The numerical simulation shows that the existence of aeolian sand-cement/fly ash paste backfill inevitably altered the coalescence type and failure mode of the specimens and had a strengthening effect on the shear strength of backfill-rock composites. Based on damage mechanics and statistics, a shear constitutive model was proposed to describe the shear fracture characteristics of specimens, especially the bimodal phenomenon. Finally, the micro- and meso-mechanisms of shear failure were discussed by combining the micro-test and numerical results. The research can advance the better understanding of the shear behavior of backfill-rock composites and contribute to the safety of mining engineering.

Effect of roughness, contact pressure and lubrication on the onset of galling of the 6082 aluminium alloy in cold forming, a numerical approach

The effect of surface roughness, contact pressure and lubrication on the onset of galling of aluminum 6082-T6 is studied with a pin-on-plate tribometer. The design of experiments involves pins with mean arithmetic roughness Ra equaled to 0.2, 0.35 and 0.6 μm, normal loads ranging from 5 to 600 N, and 4 different lubrications: without lubricant, with MoS2 dry lubricant, with pure mineral oil and with a highly chlorinated paraffin oil. Tests are performed at room temperature and are repeated three times. Experimental results show the great sensitivity of the onset of galling to the roughness and the beneficial effect of dry and liquid lubricants. The occurrence of galling is study by optical micrographs, by the analyses of the coefficient of friction, and by the use of finite element simulations. It comes that the variation of the coefficient of friction is not self-sufficient to detect the onset of galling. The finite element computations involves Wilson’s lubrication model and Xue’s damage model. Galling is assumed when finite elements near the contact area reach the critical damage Dc. This numerical approach leads to a good prediction of the onset of galling for the tests performed under constant normal load. For tests performed with increasing normal loads and various lubricants, the numerical prediction overestimate the sliding length before galling occurs.

Tribological behavior of diamond coated reaction-bonded silicon carbide under dry and seawater environment

Ceramic seal materials such as Silicon carbide (SiC) and Reaction-Bonded SiC (89%SiC and 11 % free Silicon) are widely used in mechanical pumps, compressors, and feed water pumps to prevent the fluid leakage between the two rotating shafts. In a continuously harsh environment, these mechanical seal materials undergo high friction and wear due to the high asperity-to-asperity contact between the two mating parts and generate high frictional heat at the interface. This scenario induces seal failure under high operating conditions. Especially in corrosive mediums such as acids, high pH value solutions, and hard abrasive media can cause aggressive seal failure. To reduce production downtime and improve the longevity of the mechanical seal, the surface of the seal material needs to be engineered with a suitable coating that will satisfy the required properties of high hardness, chemically inertness, and low friction coefficient. In this regard, we have come up with a super hard coating material such as diamond (Micro-crystalline) on the surface of Reaction-Bonded SiC using the hot filament CVD (HFCVD) method to meet the above-required properties. In this work, we have carried out a systematic study on the tribological effect of uncoated, and diamond-coated seal material against silicon nitride ceramic under a dry and seawater environment. The initial physical characteristics such as surface morphology, surface roughness, and Raman analysis were performed on the samples before and after coating. To understand the friction and wear characteristics, the linear reciprocating tribometer test (Ball on Flat) was conducted on the uncoated and diamond-coated samples using a universal tribometer for an operating period of 36,000 cycles. The experimental results show that the diamond-coated sample exhibits a low friction coefficient (0.05 ± 0.01) compared to the uncoated sample (Friction coefficient (CoF) = 0.24 ± 0.037) at a normal load of 10 N with a frequency of 10 Hz under a seawater environment. Similarly, under dry conditions for the same tribo-test parameters, the diamond-coated sample (CoF = 0.06 ± 0.02) outperforms compared with the uncoated sample (CoF = 0.42 ± 0.17) at a percentage improvement of 85 %. From the observed results, we conclude that diamond-coated ceramic seals are considered a suitable alternative to commercially available seals in terms of high operating conditions and durability under both wet (seawater) and dry running operations.

High thermal conductivity and ultralow friction of two-dimensional ice by molecular dynamics simulations

Two-dimensional ice (2D ice) is a relatively new family member of ice polymorphs. While the phase transitions and growth kinetics of 2D ice have aroused intensive investigation, its thermal and mechanical properties are seldom studied. The unique 2D structure of this polymorph suggests that it may possess distinct physical characteristics compared to its bulk counterparts. In this work, the thermal conductivities and friction of 2D ice were systematically studied by molecular dynamics (MD) simulations. It was found that the thermal conductivities of 2D ice show a strong dependence on their length and the extrapolated value of the infinite system can achieve ∼4.7 W/(m∙K), which is notably higher than that of bulk phase of ice Ih ∼1.5 W/(m∙K). Decreasing temperature or applying mechanical strains can both increase the thermal conductivity of 2D ice, which can be explained by structure or phonon analyses. 2D ice also exhibits an ultralow friction of ∼0.24 nN when sliding upon a graphene substrate, lower than that of ice Ih ∼0.70 nN at the same sliding conditions. With the decrease in temperature or the increase in normal load, the friction coefficient of 2D ice exhibits a downward trend, and it could be as low as ∼0.005, indicating superlubricity. The analysis on structural lubricity suggests that ordered but mismatched crystal-crystal contacts have lower friction than disordered case. The results on high thermal conductivity and ultralow friction would guide the potential application of 2D ice in efficient thermal management or design of nanofluidic devices.

Enhancing tribological performance of graphene sheet-embedded carbon films on steel substrates via texture engineering and chromium doping

Amorphous carbon (a-C) film is a promising solid lubricant coating due to its unique structure and excellent properties. However, its poor adhesion and long running-in period hinder the application in metal components. Graphene sheet-embedded carbon (GSEC) film has a significantly shorter running-in period but suffers from inferior tribological properties due to its rough surface and weak mechanical characteristics. In this study, we utilized an electron cyclotron resonance (ECR) plasma nano-surface manufacturing device to deposit GSEC films onto steel substrate surfaces. By manipulating the surface/interface texture and incorporating chromium (Cr) doping, the tribological properties of the GSEC films were improved both chemically and physically. The results demonstrated that the textured carbon film exhibited superior adhesion to the steel substrate and a wear life that was three orders of magnitude longer than the untextured GSEC film, under low normal load conditions while sliding against the GCr15-bearing steel ball. After doping the Cr into textured carbon films, there was a significant reduction in the friction coefficients, and the wear type of carbon film transformed from adhesive wear to abrasive wear. Moreover, the doped carbon films demonstrated prolonged wear lives under high normal loads. This improvement can be attributed to the formation of hard CrC nanocrystalline, which effectively reduced surface roughness and enhanced the mechanical properties of the carbon films. Notably, even under a contact pressure of 0.83 GPa, the doped carbon film maintained favorable tribological performances. These findings have extended the potential applications of carbon films on metal substrates.

The Influence of Fin Thread Implant Design on Stress Distribution Comparative FEA StudyFaaiz

Background: one of the requirements of long term dental implant success lies within the implant structure and bone- implant interface ability to cope with functional stress. Dental implant ability to withstand different occlusal loads optimizes implant-supported prosthesis function, minimize stress over the surrounding bone, improve osseointegration and reduce the required period for implant loading. One of the areas of research on implant geometry is the thread design. Threads increase initial bone contact, enhance implant stability, maximize implant surface area with subsequent improvement of osseointegration. Recently, Fin Thread (FT) and Modified Fin Thread designs (IBS®) have been introduced. These designs on TiG5 dental implant did not seem to receive adequate attention in the current literature. Methods: four dental implant models (Modified Fin Thread, Fin Thread, V-shaped and Buttress designs) of TiG5 were tested using FEA for stress distribution using normal and extreme static occlusal loads on 0, 15 and 25ο angles. Results: Modified Fin Thread (MFT) design and Fin Thread (FT) design showed almost uniform stress distribution compared to other models under normal occlusal load. However, MFT design showed better stress distribution with no cortical bone involvement in overloaded occlusal stress (200 and 400N) respectively. Conclusion: Modified Fin Thread Design of Ti G5 seems to be the more suitable dental implant model in terms of stress distribution in normal and over occlusal load conditions. MFT designs need clinical studies to support this study findings on patients with long follow up periods.

Analysis and design of a novel segmented energy absorbing steel plate shear wall system

A steel plate shear wall (SPSW) system capable of providing strength and stiffness under normal load conditions and dissipating energy under extreme load conditions is proposed. The infill plate of this proposed Segmented Energy Absorbing SPSW (SEA-SPSW) system consists of two trapezoidal plate segments. For each plate segment, one edge is connected to the beam while the opposite edge is joined together by steel strips. The steel strips are held together using high strength bolts with long-slotted holes. Under normal load conditions, the SEA-SPSW behaves like a conventional SPSW. However, under extreme load conditions, the plate segments will slide between the steel strips and dissipate energy through friction. Because the proposed system does not rely on yielding or buckling to dissipate energy, it can be reset and reused after a severe load event. The behavior of this SEA-SPSW is studied using finite element and compared to an all steel conventional SPSW system. It is found that the proposed system not only helps reduce inter-story displacement, it also offers a desirable equivalent viscous damping ratio as well as a rather favorable energy dissipation to mass ratio.

Friction and damage of carbon fiber in tow-metal friction during the formation of flexible-oriented three-dimensional composite preforms

As the main structure of fiber-reinforced composite, the preform affected the mechanical properties of the composite. The forming of preforms is associated with the damage of fiber due to tow-metal friction, which can compromise the properties of the composite component. This study simulated the frictional behavior of carbon fibers during flexible-oriented three-dimensional woven process to reveal the mechanism of damage and determine the process window, and the effects of processing-related parameters on friction and carbon fiber were discussed. The normal load and pre-tension played a dominant role in generation of hairiness and wear, while the weaving speed had a minimal effect. The different parameters affected the damage of tow by changing the contact area between filament and metal. According to the results, the process window of pre-tension on filament was set to [0.083 mN, 0.183 mN]. The normal load should be within the window of pre-tension, as normal load was determined by pre-tension. The process window of weaving speed was set to [1 Hz, 5 Hz]. The optimized process parameters could improve the tensile strength of woven carbon fiber by 25.7%.

High-temperature tribological properties of Co-29Cr-6Mo alloy fabricated by selective laser melting process

This paper discusses the experimental procedure and results of an investigation into the sliding wear behavior of Co-Cr-Mo specimens produced by selective laser melting (SLM) process. The sliding wear tests were carried out with different normal loads, sliding frequencies, and temperatures. The results showed that the coefficient of friction decreased as the applied normal load increased due to the temperature effect. The wear rate increased significantly at higher loads due to increased surface stresses. Testing the specimens at elevated temperatures resulted in a decrease in COF due to thermal softening and the formation of an oxide layer on the surface. The wear rate increased for specimens tested at 200°C due to a decrease in hardness and strength, but the wear rate decreased at higher temperatures due to the protective effect of the oxide layer. The obtained results showed the SLM-printed Co-Cr-Mo alloy exhibited good mechanical properties and wear resistance, making it a promising material for tribological applications, especially at elevated temperatures.

Buckling analysis of stiffened functionally graded multilayer graphene platelet reinforced composite plate with circular cutout embedded on elastic support subjected to in-plane normal and shear loads

Buckling analyses of orthogonally stiffened functionally graded graphene platelet reinforced composite plate with circular cutout supporting on Winkler elastic foundation is conducted according to the third order shear deformation plate theory and the finite element method to achieve the desired solutions. Material properties of the composite plate are evaluated using Rule of mixture and Halpin-Tsai approach. Graphene platelet reinforcements and Poly methyl methacrylate matrix are considered as the two components of the composite media. The material of the stiffeners is selected the same as that of the polymer matrix. In one efficient case, adding a set of stiffeners increased the critical buckling load by 41.8 % with only a 10.3 % increase in weight of the structure. Influence of broad range of factors such as GPLs nanofillers distribution pattern and weight fraction, Winkler-type elastic foundation, uniaxial and biaxial normal and shear loads, plate thickness and aspect ratio, width, height and number of longitudinal and transverse stiffeners are reported in several tabular and graphical data in detail.