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Material loss due to wear plays a key role in the service life of rubber components in various tribological applications, such as tires, shoe soles, wiper blades, to name a few. It also adversely affects energy consumption, economy, and CO2 emissions around the globe. Therefore, understanding and modeling the wear behavior of rubbers are important in the design of economic and environment-friendly rubber compounds. In this study, we investigated the effect of normal load and sliding velocity on the wear rate of rubber compounds widely used in the tire treads and evaluated the wear models previously proposed for rubbers to determine the best model to predict the rubber wear rate. The sliding wear rates of different types of Styrene-Butadiene Rubber (SBR) and Isoprene Rubber (IR) compounds on a broom finish concrete slab were measured for different sliding velocities and normal loads. The experimental results were used to evaluate and discuss different wear models proposed in the literature. A new empirical model was proposed to predict the wear rate by considering mechanical properties associated with rubber wear. The experimental results revealed that the wear rate of rubber compounds non-linearly depends on the normal load or friction force, while the effect of sliding velocity on the wear rate is not significant in the 20–100 mm/s range. Moreover, traces of both mechanical (abrasion) and chemical (smearing) wear were observed on all rubber compounds.

Piezoresistive structures inspired by serpentines, auxetic, and kirigami arrangements have demonstrated good flexibility and sensitivity under tension. Piezoresistive structures display optimal performance when the characteristics entail reliable stretchability and repeatability. These structures can be implemented as wearable sensors by compressing and elongating the conductive nanocomposites to vary the flow of electrons and to provide resistance change. To guarantee the reliability of these structures for strain sensing, it is important that the resistance change in these structures remains constant under repeated loads. In this study, the performance of different piezoresistive structures under cyclic tensile load is investigated and compared. Based on the performance of different types of structures, novel hybrid structures have been also proposed to design for both high stretchability and sensitivity of piezoresistive sensors. All the structures were tested with position limits rather than a fixed force to avoid permanent deformation. First, small position limits were used to determine Young’s Modulus, then a 10-cycle tensile test with larger position limits was used to further study the electromechanical behavior of different piezoresistive structures under larger deformation and repetition. Finally, the gage factor was derived for all the studied structures, and they were re-categorized based on properties’ similarities.

The surge of growth in additive manufacturing (AM) has brought about increased interest in smart devices and advanced manufacturing. Fused Filament Fabrication (FFF) often presents itself as the starting equipment for industrial applications and hobby enthusiasts. The introduction of conductive polymer composites into FFF has brought about widespread capabilities, particularly in the areas of flexible sensors, printed electronics, and other multi-functional materials. Piezoresistive sensors have especially been of interest due to their use in wearable electronics and structural health monitoring coupled with the increasing commercial availability of conductive thermoplastic filaments. However, while much research has been devoted to the geometrical parameters in piezoresistive sensors in conventional manufacturing, little has been investigated with respect to additive manufacturing. Here, we present a unique method for tailoring the sensitivity of FFF produced flexible pressure sensors by altering the infill printing settings, therefore affecting the electromechanical response. Sensors were printed using common infill patterns (Concentric, Grid, Gyroid, Honeycomb, Lines, and Cubic) and low infill percentages (5–15%) capable of sensitivities of 2,010 kPa−1 under an applied pressure of up to 60 kPa and 530 kPa−1 under an applied pressure of up to 950 kPa. This work demonstrates the ease-of-fabrication and performance of flexible pressure sensors using an inexpensive and simple fabrication method.

The implementation of Industry 4.0 tools and technologies in many companies coupled with the impact of those tools and technologies in the product design and development process is creating a demand for engineering graduates that have basic competencies (i.e., knowledge, skills, and abilities) related to Industry 4.0 when they join the workforce. This paper presents key Industry 4.0 competencies that were selected for a new mechanical engineering program at Texas State University. For each competency, the level in Bloom’s taxonomy that students are expected to attain at the time of graduation is defined taking into consideration that the implementation of Industry 4.0 tools and technologies is a multidisciplinary endeavor that involves professionals from different majors. The paper also provides information about the implementation plan that will be used to incorporate the competencies selected in the undergraduate curriculum.

Modeling the real contact area plays a key role in every tribological process, such as friction, adhesion, and wear. Contact between two solids does not necessarily occur everywhere within the apparent contact area. Considering the multiscale nature of roughness, Persson proposed a theory of contact mechanics for a soft and smooth solid in contact with a rigid rough surface. In this theory, he assumed that the vertical displacement on the soft surface could be approximated by the height profile of the substrate surface. Although this assumption gives an accurate pressure distribution at the interface for complete contact, when no gap exists between two surfaces, it results in an overestimation of elastic energy stored in the material for partial contact, which typically occurs in many practical applications. This issue was later addressed by Persson by including a correction factor obtained from the comparison of the theoretical results with molecular dynamics simulation. This paper proposes a different approach to correct the overestimation of vertical displacement in Persson’s contact theory for rough surfaces with self-affine fractal properties. The results are compared with the correction factor proposed by Persson. The main advantage of the proposed method is that it uses physical parameters such as the surface roughness characteristics, material properties, sliding velocity, and normal load to correct the model. This method is also implemented in the theory of rubber friction. The results of the corrected friction model are compared with experiments. The results confirm that the modified model predicts the friction coefficient as a function of sliding velocity more accurately than the original model.

In this paper, a novel portable sliding friction and wear test rig is introduced. Unlike other laboratory-based test setups, this setup can be used for both indoor and outdoor experiments. There is also no limitation on the size and type of the substrate surface that can be used for the friction and wear test in contrast to typical test rigs, which have some limitations for the size and type of substrate surface. A small six-wheel ground robot is developed to drag the sample on an arbitrary surface for a desired distance and velocity. A ground robot is an unmanned ground vehicle, capable of driving on the ground without humans on board. The speed of this robot can be measured and controlled precisely. The nominal normal load is adjusted using dead weights placed on the sample holder and the friction force is measured using a load cell. An adjustable sample holder was also designed and built to hold different-size specimens. The results of styrene–butadiene rubber block sliding on an asphalt track are presented to validate the test setup and illustrate the potential of the system for friction and wear testing. In addition, the effect of sliding velocity on the friction and wear is studied, and the correlation between the wear rate and the friction coefficient is investigated. These experimental results can be used to estimate the friction and life span of a tire tread compound on the real asphalt road. Finally, the formation of abrasion pattern observed on the rubber surface sliding on an asphalt track is discussed, which provides an insight into the understanding of dominant wear mechanism of tire tread compound on typical asphalt surfaces.

Tribological behavior of Styrene-Butadiene Rubber (SBR) compound reinforced by silica and carbon-black fillers on two different asphalt-like surfaces is studied using theoretical and experimental approaches. Linear sliding friction and wear tests were performed on two different roofing asphalt papers. The surface roughness power spectra of asphalts and the master curves of the large-strain viscoelastic modulus of SBR compound were used to model the contact area and friction coefficient theoretically. The theoretical results are in good agreement with experiment providing the tribochemical degradation is not the dominant wear mechanism. When the formation of a tribo-modified layer prevails the mechanical abrasion, the wear rate, in terms of mass loss, does not necessarily increase with the increase of frictional work as expected theoretically.

Background: The coronavirus disease 2019 (COVID-19) presents various phenotypes from asymptomatic involvement to death. Disseminated intravascular coagulopathy (DIC) is among the poor prognostic complications frequently observed in critical illness. To improve mortality, a timely diagnosis of DIC is essential. The International Society on Thrombosis and Hemostasis (ISTH) introduced a scoring system to detect overt DIC (score ≥5) and another category called sepsis-induced coagulopathy (SIC) to identify the initial stages of DIC (score ≥4). This study aimed to determine whether clinicians used these scoring systems while assessing COVID-19 patients and the role of relevant biomarkers in disease severity and outcome. Materials and Methods: An exhaustive search was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses, using Medline, Embase, Cochrane, CINAHL, and PubMed until August 2020. Studies considering disease severity or outcome with at least two relevant biomarkers were included. For all studies, the definite, maximum, and minimum ISTH/SIC scores were calculated. Results: A total of 37 papers and 12,463 cases were reviewed. Studies considering ISTH/SIC criteria to detect DIC suggested a higher rate of ISTH ≥5 and SIC ≥4 in severe cases and nonsurvivors compared with nonsevere cases and survivors. The calculated ISTH scores were dominantly higher in severe infections and nonsurvivors. Elevated D-dimer was the most consistent abnormality on admission. Conclusion: Higher ISTH and SIC scores positively correlate with disease severity and death. In addition, more patients with severe disease and nonsurvivors met the ISTH and SIC scores for DIC. Given the high prevalence of coagulopathy in COVID-19 infection, dynamic monitoring of relevant biomarkers in the form of ISTH and SIC scoring systems is of great importance to timely detect DIC in suspicious patients.

Coagulopathy and derangements in the coagulation parameters are significant features of COVID-19 infection, which increases the risk of disseminated intravascular coagulation, thrombosis, and hemorrhage in these patients, resulting in increased morbidity and mortality. In times of COVID-19, special consideration should be given to patients with concurrent chronic kidney disease (CKD) and COVID-19 (CKD/COVID-19 patients) as renal dysfunction increases their risk of thrombosis and hemorrhage, and falsely affects some of the coagulation factors, which are currently utilized to assess thrombosis risk in patients with COVID-19. Hence, we believe extra attention should be given to determining the risk of thrombosis and bleeding and optimizing the timing and dosage of anticoagulant therapy in this unique population of patients. CKD/COVID-19 patients are considered a high-risk population for thrombotic events and hemorrhage. Furthermore, effects of renal function on paraclinical and clinical data should be considered during the evaluation and interpretation of thrombosis risk stratification. Individualized evaluation of clinical status and kidney function is necessary to determine the best approach and management for anticoagulant therapy, whereas there is a lack of studies about the population of CKD/COVID-19 patients who need anticoagulant therapy now.

Chemotherapy-associated renal injury is considered one of the major concerns among nephrological and oncological practice. The use of novel anti-neoplastic therapies that target carcinomas has helped in the detection of this form of renal injury. Immune checkpoint inhibitors (ICPIs) are a group of monoclonal antibodies targeting inhibitory receptors that exist on tumor cells and T cells. ICPIs are able to suppress tumors that might have escaped from the immune surveillance. Meanwhile, although ICPIs have shown promising efficacy in cancer treatment, their immune-related side effects limit their widespread use in cancer therapy schedules. One of the major side effects limiting ICPIs’ usage is nephrotoxicity. Glomerular disease, acute interstitial nephritis (AIN), and acute tubular necrosis (ATN) are considered different infusion-related adverse events. Infiltration of eosinophils, T lymphocytes, and plasma cells, as well as interstitial inflammation and edema, leading to acute tubulointerstitial nephritis (ATIN). It is conceivable that the rupture of self-tolerance by ICPIs induces an autoimmune reaction against some specific self-antigens in the organs including kidneys. The exact nature of the antigen is unclear; however, it is possible that it is found in the renal tubular cells, as indicated by a greater frequency of ATIN in kidney biopsies. The current review paper discusses the relationship between ICPIs therapy and kidney disorders or more specifically, their possible role in renal damage along with renal toxicity profile in the setting of ICPIs treatment.

Lack of driver’s knowledge about the abrupt changes in pavement’s friction and poor performance of the vehicle’s stability, traction, and ABS controllers on the low friction surfaces are the most important factors affecting car crashes. Due to its direct relation to vehicle stability, accurate estimation of tire-road friction is of interest to all vehicle and tire companies. Many studies have been conducted in this field and researchers have used different tools and have proposed different algorithms. This literature survey introduces different approaches, which have been widely used to estimate the friction or other related parameters, and covers the recent literature that contains these methodologies. The emphasize of this review paper is on the algorithms and studies, which are more popular and have been repeated several times. The focus has been divided into two main groups: experiment-based and model-based approaches. Each of these main groups has several sub-categories, which are explained in the next few sections. Several summary tables are provided in which the overall feature of each approach is reviewed that gives the reader the general picture of different algorithms, which are widely used in friction estimation studies.

Integrating nano-sized reinforcing materials into carbon fiber polymer composites (CFRPs) could enhance several aspects of their mechanical performance; e.g., interfacial strength, delamination resistance and vibrations attenuation. In this study, ZnO nanorods were grown on the surface of carbon fibers to create hybrid reinforcements. The hydrothermal synthesis of ZnO nanorods was tuned such that relatively long (>2.0 μm) nanorods can be grown. This synthesis technique requires pre-deposition of a thin seeding layer of ZnO particulates on the carbon fibers to initiate the ZnO nanorods growth. Depending on the method by which the seeding layer is deposited, the grown ZnO nanorods could display different morphologies. In this study, two different techniques were utilized to pre-deposit the ZnO seeding layer on the carbon fibers; ZnO nanoparticles/solution mixture airbrush spraying, and magnetron sputtering. The carbon fibers pre-coated with the airbrush spraying method yielded forests of randomly oriented ZnO nanorods, while the fibers pre-coated via the sputtering technique exhibited radially aligned ZnO nanorods forests. Hybrid CFRPs were fabricated based on the aforementioned carbon fiber fabrics and tested via 3-point bending dynamic mechanical analysis (DMA) and quasi-static tension tests. The loss tangent of the CFRPs, which delineates the damping capability, increased by 28% and 19% via radially and randomly grown ZnO nanorods, respectively. The in-plane tensile strength of the hybrid CFRPs were improved by 18% for the composites based on randomly oriented ZnO nanorods over the carbon fibers. The fractographs of the tension samples were also captured to reveal the role of the long ZnO nanorods in the in-plane performance of the hybrid CFRPs.

Friction and wear of viscoelastic materials like rubbers are topics of extreme practical importance such as the construction of tires, shoe heels and soles, rubber O-ring seals, and wiper blades. Friction of viscoelastic materials differs from the frictional properties of the elastic solids as friction is directly related to energy dissipation via the internal damping of such materials while purely elastic materials do not dissipate energy. Based on hysteresis properties of viscoelastic materials, physics based multiscale models were developed by Persson for fiction [1, 2] and powdery wear [3] of rubbers sliding on rough surfaces. In this research, these theories were studied and the theoretical results were compared with experimental results obtained from a dynamic friction/wear tester. The inputs to the theoretical models were the fractal properties of the rough surface, the dynamic modulus, and the fatigue behavior of the viscoelastic material. The fractal properties of the rough surface was obtained from the 3D profile of the surface measured using an optical profilometer. The dynamic modulus of the rubber samples was characterized via dynamic mechanical analysis at different frequencies and temperatures. The fatigue crack growth behavior of the samples were found from experimental results of crack propagation versus tearing energy obtained from the fatigue test. Then, the friction coefficient between different rubber samples and rough surfaces was calculated as a function of sliding velocity using both analytical model and experimental approach. In the dynamic friction/wear tester, normal force was adjusted and measured accurately, in addition, the frictional force was measured using a load cell in longitudinal direction along the sliding axis. The experimental sliding friction coefficient was calculated as the ratio of longitudinal force at a constant velocity to the normal force. The mass loss of rubber sample was measured by weighting the sample before and after each test to obtain the wear rate. The comparison between experimental and analytical results showed that the friction model could predict the friction coefficient accurately while the theory of powdery wear is unable to capture all the physics involved in rubber wear on rough surfaces.

Good understanding of friction in tire-road interaction is of critical importance for vehicle dynamic control systems. Most of the friction models proposed to describe the friction coefficient between tire-treads and road surfaces have been developed based on empirical or semi-empirical relations that are not able to include many effective parameters involved in the tire-road interactions. Therefore, these models are just useful in limited conditions similar to the experiments, and do not accurately represent tire-road traction in numerical tire models. However, in last two decades, a few theoretical models have been developed to calculate the tire-road friction coefficient theoretically by considering both viscoelastic behavior of tire tread compounds and multi-scale interactions between tire treads and rough road surfaces. In this article, a novel physics-based model proposed by Persson has been investigated and used to develop computer algorithms for calculation of sliding friction coefficient between a tire tread compound and a rough substrate. The viscoelastic behavior of tread compound and the surface profile of rough counter surface are the inputs of this physics-based theoretical model. The numerical results of the model have been compared with the experimental results obtained from a dynamic friction tester designed and built in the Center for Tire Research (CenTire). Good agreement between numerical results of theoretical model and experimental results has been found at intermediate range of slip velocities considering the effect of adhesion and shearing in the real contact area in addition to hysteresis friction due to internal energy dissipation in the tire tread compound.

There is a major concern with aging and fretting wear in the transportation industry. The presence of an edge crack in structures can be tolerated if its evolution is predicted using fracture mechanics. In this study, the digital image correlation (DIC) technique was employed to evaluate the in-plane stress intensity factors (SIFs), KI and KII, for the contact between a half plane with an edge crack and an asymmetric tilted wedge. DIC requires two digital images of the same sample at different stages of loading to measure the corresponding displacements and strain fields. A computer code was developed to process the captured images and determine the correlation coefficients. Fracture mechanics theory was then applied to calculate the SIFs from displacement fields obtained via DIC analysis. The effect of the wedge tip angle on the SIFs was studied using DIC. To highlight the advantages of DIC, a photoelasticity method was also employed to determine SIFs for the identical problem. The SIF values from the two techniques were compared and a good agreement was observed. In summary, it was shown that although the DIC method requires simple setup and minimal sample preparation relative to the alternatives, it provides reliable results.

Photoelasticity was utilized as an experimental stress analysis tool to determine the stress intensity factors for the contact problem between a half-plane with an edge crack and an asymmetric tilted wedge. The effect of contact force magnitude as well as the angle, length, and position of the crack on mode I and II stress intensity factors were studied and discussed. Analysis of the experimental results is based on fracture mechanics, optical properties of materials, and the correlation between fringe patterns and the distribution of stress in transparent materials (i.e., polycarbonate). Image processing was utilized to extract details from the images acquired from the plate under loading. The finite element method was also used to calculate the stress intensity factors. Experimental and finite element results were in good agreement; however, there are some limitations on the application of photoelasticity method.

Structural health monitoring can enhance reliability, increase safety, and decrease maintenance costs by detecting damage at an early stage. By taking advantage of the electromechanical coupling, piezoelectric materials have the potential to harvest energy from ambient vibration sources to provide low-power electricity for self-powered electronic devices. In comparison with other piezoelectric transducers, zinc oxide (ZnO) nanowires carry the added advantages of structural flexibility, lower cost, compactness, and lighter weight. In this study, the energy harvesting capabilities of nanoscale ZnO piezoelectric nanowires (NW) grown on the surface of glass fiber fabrics are investigated experimentally. A series of cantilevered carbon fiber beams containing a controlled amount of ZnO nanowires is evaluated. The absolute electrical energy dissipation is quantified by measuring the output power over a broad spectrum of known vibratory loads and frequencies. The maximum amount of power extracted is obtained by employing resistive impedance matching. Here, a maximum peak of ∼6.7 mV was generated when the beam containing ZnO nanowires was excited at 2.90g and connected to a 10 MΩ load. At that excitation level, a maximum of 20.0 pW was generated when an optimal resistor of 1 MΩ is connected. A tip mass of ∼0.6 gram added to the sample with ZnO NWs increased the peak-voltage by 2.21 mV and increased the peak-power by 13.3 pW. A series of DC voltage applied to the ZnO sample suggests the equivalence of poling treatment, where the dipole alignment of the ZnO NWs are disrupted. Here, a maximum peak-power of 45 pW is reported, showing promising potential of scaling-up to harvest ambient energy for low-powered electronics.Copyright © 2015 by ASME