Browsing by Subject "Friction"

Now showing 1 - 7 of 7
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    Anisotropic Properties of Articular Cartilage in an Accelerated In Vitro Wear Test
    (Elsevier, 2020-09) Hossain, M. Jayed; Noori-Dokht, Hessam; Karnik, Sonali; Alyafei, Naomi; Joukar, Amin; Trippel, Stephen B.; Wagner, Diane R.; Mechanical and Energy Engineering, School of Engineering and Technology
    Many material properties of articular cartilage are anisotropic, particularly in the superficial zone where collagen fibers have a preferential direction. However, the anisotropy of cartilage wear had not been previously investigated. The objective of this study was to evaluate the anisotropy of cartilage material behavior in an in vitro wear test. The wear and coefficient of friction of bovine condylar cartilage were measured with loading in directions parallel (longitudinal) and orthogonal (transverse) to the collagen fiber orientation at the articular surface. An accelerated cartilage wear test was performed against a T316 stainless-steel plate in a solution of phosphate buffered saline with protease inhibitors. A constant load of 160 N was maintained for 14000 cycles of reciprocal sliding motion at 4 mm/s velocity and a travel distance of 18 mm in each direction. The contact pressure during the wear test was approximately 2 MPa, which is in the range of that reported in the human knee and hip joint. Wear was measured by biochemically quantifying the glycosaminoglycans (GAGs) and collagen that was released from the tissue during the wear test. Collagen damage was evaluated with collagen hybridizing peptide (CHP), while visualization of the tissue composition after the wear test was provided with histologic analysis. Results demonstrated that wear in the transverse direction released about twice as many GAGs than in the longitudinal direction, but that no significant differences were seen in the amount of collagen released from the specimens. Specimens worn in the transverse direction had a higher intensity of CHP stain than those worn in the longitudinal direction, suggesting more collagen damage from wear in the transverse direction. No anisotropy in friction was detected at any point in the wear test. Histologic and CHP images demonstrate that the GAG loss and collagen damage extended through much of the depth of the cartilage tissue, particularly for wear in the transverse direction. These results highlight distinct differences between cartilage wear and the wear of traditional engineering materials, and suggest that further study on cartilage wear is warranted. A potential clinical implication of these results is that orienting osteochondral grafts such that the direction of wear is aligned with the primary fiber direction at the articular surface may optimize the life of the graft.
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    Bracket, ligation, and misaligned straight wires effects on load systems during orthodontic sliding mechanics
    (2015-07) Hannah, Richard D.; Katona, Thomas R.
    Objective: The objectives of this study were to measure and compare the complete, not solely friction, load components (forces and moments) experienced by brackets as they slide along straight wires that are angled relative to the path of bracket travel. Materials and Methods: Three types of brackets (stainless steel mandibular canine and central incisor, and an all-ceramic mandibular canine) were ligated with stainless steel or elastomeric modules to 2 sizes of stainless steel wire (0.021” x 0.021” and 0.016” x 0.016”) at 0°, 1° and 2° bracket-wire misalignments. All 3 force and 3 moment components experienced by the brackets were measured as they slid along the wire. Results: Overall, all 36 permutations of the 3 brackets, 2 ligations, 2 wires and 3 alignments produced statistically different (predominantly P < .0001) load components on the bracket. Conclusions: The type of bracket, wire, ligation, and relatively small misalignments (1° and 2°) between bracket and wire affect all force and moment components applied to the bracket. Traditional friction-focused “pull through” studies miss the attendant effects on the other 5 load components.
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    Correlation analysis of cartilage wear with biochemical composition, viscoelastic properties and friction
    (Elsevier, 2023) Joukar, Amin; Creecy, Amy; Karnik, Sonali; Noori-Dokht, Hessam; Trippel, Stephen B.; Wallace, Joseph M.; Wagner, Diane R.; Orthopaedic Surgery, School of Medicine
    Healthy articular cartilage exhibits remarkable resistance to wear, sustaining mechanical loads and relative motion for decades. However, tissues that replace or repair cartilage defects are much less long lasting. Better information on the compositional and material characteristics that contribute to the wear resistance of healthy cartilage could help guide strategies to replace and repair degenerated tissue. The main objective of this study was to assess the relationship between wear of healthy articular cartilage, its biochemical composition, and its viscoelastic material properties. The correlation of these factors with the coefficient of friction during the wear test was also evaluated. Viscoelastic properties of healthy bovine cartilage were determined via stress relaxation indentation. The same specimens underwent an accelerated, in vitro wear test, and the amount of glycosaminoglycans (GAGs) and collagen released during the wear test were considered measures of wear. The frictional response during the wear test was also recorded. The GAG, collagen and water content and the concentration of the enzymatic collagen crosslink pyridinoline were quantified in tissue that was adjacent to each wear test specimen. Finally, correlation analysis was performed to identify potential relationships between wear characteristics of healthy articular cartilage with its composition, viscoelastic material properties and friction. The findings suggest that stiffer cartilage with higher GAG, collagen and water content has a higher wear resistance. Enzymatic collagen crosslinks also enhance the wear resistance of the collagen network. The parameters of wear, composition, and mechanical stiffness of cartilage were all correlated with one another, suggesting that they are interrelated. However, friction was largely independent of these in this study. The results identify characteristics of healthy articular cartilage that contribute to its remarkable wear resistance. These data may be useful for guiding techniques to restore, regenerate, and stabilize cartilage tissue.
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    The effects of bracket, wire conformation and size on the load systems during orthodontic sliding mechanics
    (2015-07) Mika, David E.; Katona, Thomas R.
    Objective: The purpose of this laboratory study was to compare all 6 load components (3 force and 3 moment) acting on 2 different stainless steel brackets as they slide along 3 sizes of stainless steel archwires with 3 different conformations. Materials and Methods: Brackets were attached to a load cell and elastomeric ligated to the wires. As the load cell was pulled along a precision track, the 6 load components (forces and moments in the 3 orthogonal coordinate system) acting on the bracket were recorded. ANOVA was applied to the data. Results: Overall, there were significant differences for all effects (bracket, wire size and wire configuration), for all outcomes (the loads), except the effect of bracket on the force of friction and one of the moment components. Conclusion: The results demonstrate that the force of friction associated with sliding mechanics should not be considered in isolation, because factors that affect it also affect the other 5 load components.
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    Factors influencing cartilage wear in an accelerated in vitro test: collagen fiber orientation, anatomic location, cartilage composition, and photo-chemical crosslinking
    (2018) Hossain, M. Jayed; Wagner, Diane; Jones, Alan; Holguin, Nilsson
    Articular cartilage (AC) is a strong but flexible connective tissue that covers and protects the end of the long bones. Although cartilage has excellent friction and wear properties that allow smooth joint function during daily activities, these properties are not fully understood. Many material properties of cartilage are anisotropic and vary with anatomic location and the composition of the tissue, but whether this is also true for cartilage friction and wear has not been previously determined. Furthermore, cartilage disease and injury are major health concerns that affect millions of people, but there are few available treatments to prevent the progression of cartilage degeneration. Collagen crosslinking may be a potential treatment to reduce cartilage wear and slow or prevent the progression of cartilage disease. The objectives of this thesis were to investigate the relationships between the friction/wear characteristics of cartilage and the orientation of the preferred fiber direction, the anatomic location of the tissue, the composition of the tissue, and exogenous photochemical crosslinking. In the superficial zone, AC has preferential fiber direction which leads to anisotropic material behavior. Therefore, we hypothesized that AC will show anisotropic behavior between longitudinal and transverse direction in an accelerated, in vitro wear test on bovine cartilage in terms of friction and wear. This hypothesis was proven by the quantification of glycosaminoglycans released from the tissue during the wear test, which showed that more glycosaminoglycans were released when the wear direction was transverse to the direction of the fibers. However, the hydroxyproline released from the tissue during the wear test was not significantly different between the two directions, nor was the coefficient of friction. The material properties of AC can also vary with anatomic location, perhaps due to differences in how the tissue is loaded in vivo. We hypothesized that cartilage from a higher load bearing site will give better wear resistance than cartilage from lower load bearing regions. However, no differences in friction or wear were observed between the different anatomic locations on the bovine femoral condyles. The concentration of collagen, glycosaminoglycans, cells and water in the tissue was also quantified, but no significant differences in tissue composition were found among the locations that were tested. Although wear did not vary with anatomic location, variation in the wear measurements were relatively high. One potential source of variation is the composition of the cartilage. To determine whether cartilage composition influences friction and wear, a correlation analysis was conducted. An accelerated, in vitro wear test was conducted on cartilage from bovine femoral condyles, and the tissue adjacent to the wear test specimens was analyzed for collagen, glycosaminoglycan, cell, and water content. Because wear occurs on the cartilage surface, the superficial zone of the cartilage might play an important role in wear test. Therefore, composition of the adjacent cartilage was determined in both the superficial zone and the full thickness of the tissue. A significant negative correlation was found between wear and collagen content in the full thickness of the tissue, and between the initial coefficient of friction and the collagen content in the superficial zone. This correlation suggests that variation in the collagen content in the full thickness of the cartilage partially explains differences in amount of wear between specimens. The wear resistance of cartilage can be improved with exogenous crosslinking agents, but the use of photochemical crosslinking to improve wear resistance is not well understood. Two photochemical crosslinking protocols were analyzed to improve the wear resistance of the cartilage by using chloro-aluminum phthalocyanine tetrasulfonic acid (CASPc) and 670nm laser light. The cartilage treated with the two crosslinking protocols had lower wear than the non-treated group without changing the friction properties of the cartilage.
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    Mechanical and geometric considerations for the airgapless motor
    (2018-08) Wheeler, Nathan W.; Rovnyak, Steven
    The purpose of this thesis is to perform modeling from different perspectives for an airgapless motor. The airgapless motor is a proposed type of electric machine whose purpose is to replace hydraulic machines in low speed high torque applications. Because of the nature of the movement for this device, modeling of this device is atypical to the modeling done with other electric machines. This thesis will present the operating principle of the airgapless motor and take an analytical approach to modeling the torque and total energy in the device. In addition, this thesis will present the power electronics necessary to drive this device and offer recommendations to maximize the torque and minimize the torque ripple. MATLAB simulations are used to verify that the conclusion of this thesis are consistent with observations made by previous publications and prototypes.
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    Perspectives of 2D MXene Tribology
    (Wiley, 2023) Rosenkranz, Andreas; Righi, Maria Clelia; Sumant, Anirudha V.; Anasori, Babak; Mochalin, Vadym N.; Mechanical and Energy Engineering, Purdue School of Engineering and Technology
    The large and rapidly growing family of two-dimensional early transition metal carbides, nitrides, and carbonitrides (MXenes) raises significant interest in the materials science and chemistry of materials communities. Discovered a little more than a decade ago, MXenes have already demonstrated outstanding potential in various applications ranging from energy storage to biology and medicine. The past two years have witnessed increased experimental and theoretical efforts toward studying MXenes’ mechanical and tribological properties when used as lubricant additives, reinforcement phases in composites, or solid lubricant coatings. Although research on the understanding of the friction and wear performance of MXenes under dry and lubricated conditions is still in its early stages, it has experienced rapid growth due to the excellent mechanical properties and chemical reactivities offered by MXenes that make them adaptable to being combined with other materials, thus boosting their tribological performance. In this perspective, we summarize the most promising results in the area of MXene tribology, outline future important problems to be pursued further, and provide methodological recommendations that we believe could be useful for experts, as well as newcomers to MXenes research, in particular, to the emerging area of MXene tribology.