18,376 research outputs found
Prediction of Sliding Wear of Artificial Rough Surfaces
No full textWhen two surfaces are brought in contact, deformation takes place at asperity level. The local pressure distribution and deformation of the contacting surfaces are importance with respect to wear. This paper describes a wear model to predict the wear of rough sliding contacts. The wear model is based on the general Archard’s wear equation in combination with finite element analysis (FEA). In this paper the roughness is represented by uniformly distributed spherical asperities. The proposed model, FE in combination with Archard’s wear law, has proven to be a powerful tool in predicting wear of rough surfaces
Accelerated wear protocols for understanding clinical wear in modern hip prostheses
No full textThe copyright of this thesis rests with the author and no quotation from it or information derived from it may be published without the prior written consent of the authorSuccess of total hip replacements is well reported however, failures as a result of wear processes and the biological response to these products continue to challenge the orthopaedic community. Lately, corrosion of metal surfaces as well as wear particles have seen particular interest with elevated blood cobalt levels widely reported in patients receiving metal-on-metal (MoM) hip replacements. Some instances have also reported this in patients with metal-on-polyethylene (MoP) components and these corrosion products are believed to contribute to hypersensitivity reactions reported. This thesis considers wear and cobalt release in MoP and MoM hip bearings tested under standard and challenging hip simulator conditions and includes an exploration of novel bearing coatings to reduce cobalt release. The incorporation of silver into these coatings may be sufficient to produce an antibacterial response, reducing the risk of mid-term infections, another reported cause of failure.
Polyethylene wear was low under standard and clinically relevant adverse conditions in 28mm and 52 mm diameter MoP bearings (less than 35 mm3/mc). Cobalt release was measurable in 28 mm diameter MoP bearings (51 ppb/mc) with higher levels produced in large 52 mm diameters (123 ppb/mc), the first time this has been reported, although cobalt release was substantially less than that observed in MoM bearings (6909 ppb/mc). Alumina abrasives introduced in the lubricant substantially damaged MoP bearings, increasing the cobalt release to 70,690 ppb after 1 mc, greater than found after edge loaded MoM bearings (19,240 ppb). The removal of these particles still produced elevated cobalt levels compared to standard conditions and increased polyethylene wear to 435 mm3/mc.
A chromium nitride (CrN) coating in MoP bearings was resistant to this abrasive damage showing no delamination in the coating, with negligible cobalt released after 7.04 mc (153 ppb) and maintained a polyethylene wear rate below 20 mm3/mc. Silver CrN coatings on both bearing surfaces of MoM components prevented cobalt release under standard conditions, with silver release after 0.17 mc up to 3,720 ppb in high silver surface coatings, although the wear was relatively high (5.24 mm3/mc). A silver CrN coating with a low concentration of silver at the surface reduced wear and was resistant to 5 mc of edge loading. It generated 241 ppb of cobalt and maintained comparable steady state wear rates (0.65 mm3/mc) to the uncoated metal while releasing 18,786 ppb silver which may be sufficient to be an effective anti-microbial agent. These coatings may provide potential clinical benefits in MoP and MoM bearings by reducing both wear and cobalt release in ideal and adverse conditions. There may also be beneficial wear products in the form of silver, although further testing of optimised coatings is required
Tissue biomechanical strength, wear resistance and recovery in C4 turfgrass species: physiological and morphological factors and innovative evaluation techniques.
No full textTurfgrass wear effects are known to be the sum of soil compaction and plant tissue injury. As such, tissue intrinsic resistance to several mechanical factors, including traction stress, is a decisive in determining the wear resistance of a turfgrass species. Wear simulation in the field can suffer from climate, soil and machinery operator error, and is always inclusive of the soil compaction factor that is one of the origins of turfgrass wear effects in the field. Lignin, dry matter, starch, sugars and silica are some of the tissue constituents and characteristics that have been associated with leaf and stem mechanical resistance, while little information is to be found concerning stolons and rhizomes. These organs not only enable C4 turfgrass species lateral growth, soil colonization and injury recovery, but are also key constituents of mature swards.
A firsts study consisted in an extensive investigation on the effective leaf, rhizome traction resistance of Cynodon dactylon L. Pers. var. dactylon x C. transvaalensis Burt-Davy cv. Tifway 419 (Cdxt), Zoysia matrella (L.) Merr. Cv. Zeon (Zm) and Paspalum vaginatum Swartz. cv. Salam (Pv), as measured with a FIFA-approved dynamometer, and correlating these results with laboratory investigations on key tissue constituents. Several aspects emerged from the present work that can be summarized as follows:
1. Tensile strength tests on leaf, rhizome and stolon tissues of Cdxt, Zm and Pv can supply useful information regarding these species’ starch, sugars, dry matter, lignin and silica content.
2. Tensile strength was more influenced by tissue constituents than by tissue dimension.
3. The results of tensile strength tests are in accordance with these species’ wear resistance as tested in previous work, with Zm stronger than Cdxt and Pv.
3. In rhizomes and stolons, tissue breakage usually occurs in the area at the intercalary meristem at the apical zone in the immediate proximity of a node.
4. Older tissues have higher tensile strength thanks to their higher lignification.
5. Starch and sugars content found in tissues is in accordance with the species’ previously observed linear growth rate, with Cdxt faster than Pv and Zm.
6. Starch content is generally inversely proportional to lignin content.
7. Stolon TSS content, and glucose in general, is a clear marker of tissue mechanical strength.
8. Lignin is the principle constituent in determining tissue tensile strength, and as such it could be used as a turfgrass wear resistance predictor in the cultivar breeding stages.
9. Silica is a constituent undermining tissue tensile strength.
10. Leaves are the plant organs with the highest silicization and the lowest lignification of tissues.
A second study consisted of testing slabs of mature canopies of the same species for wear resistance in laboratory with a Lisport machine, as adopted by FIFA for artificial turf testing. Worn slabs of turfgrass were then allowed to recover in greenhouse to fathom out percent recovery of shoots. The results of these investigations were once again plotted again laboratory investigations on key tissue constituents. Several aspects emerged from this second work that can be summarized as follows:
1. The Lisport machine can be successfully used in an effective and reproducible way to fathom out natural turfgrass wear resistance, devoid of soil compaction effects.
2. Wear resistance for C4 species as observed in the field does not necessarily coincide with the relative tissue intrinsic resistance, but rather with the initial canopy density.
3. C4 species show a wear resistance that is much higher than C3 species.
4. C3 species show a virtually nil recuperative capability (mainly due to the lack of vegetative propagation organs).
5. The species with a very high intrinsic (tissue) wear resistance are also the species with the slowest recuperation potential. This seems to be due to lower levels of starch and TSS available for recovery.
6. Starch was a clear marker of wear resistance (negatively correlated) and recovery (positively correlated).
7. Silica was a marker positively correlated with wear resistance.
8. Lignin was the clearest marker found to be positively correlated with wear resistance.
9. A more severe wear induces a higher percentage of shoot recovery, and this particular aspects deserves further investigation
Is there evidence for accelerated polyethylene wear in uncemented compared to cemented acetabular components? A systematic review of the literature
No full textJoint arthroplasty registries show an increased rate of aseptic loosening in uncemented acetabular components as compared to cemented acetabular components. Since loosening is associated with particulate wear debris, we postulated that uncemented acetabular components demonstrate a higher polyethylene wear rate than cemented acetabular components in total hip arthroplasty. We performed a systematic review of the peer-reviewed literature, comparing the wear rate in uncemented and cemented acetabular components in total hip arthroplasty. Studies were identified using MEDLINE (PubMed), EMBASE and the Cochrane Central Register of Controlled Trials. Study quality was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. The search resulted in 425 papers. After excluding duplicates and selection based on title and abstracts, nine studies were found eligible for further analysis: two randomised controlled trials, and seven observational studies. One randomised controlled trial found a higher polyethylene wear rate in uncemented acetabular components, while the other found no differences. Three out of seven observational studies showed a higher polyethylene wear in uncemented acetabular component fixation; the other four studies did not show any differences in wear rates. The available evidence suggests that a higher annual wear rate may be encountered in uncemented acetabular components as compared to cemented components
Characterisation of wear particles genarated during accelerated testing of total hip replacement
No full textPhDTotal hip replacements have been in use for over 30 years, and have shown great
improvement from design to surgery since the first generation of implants were introduced.
The greater need for hip replacements has led to the development of test methods that can
be applied in the lab, which can predict the lifetime of a particular implant. To achieve this
aim this study has sought to investigate key parameters, which may affect wear and its
subsequent effect upon the production of particles for various material combinations and
bearing geometries, under high (jogging) and low (walking) loads, with concurrent
assessment of wear reduction, particle size and morphology.
The clinical use of cross-linked polyethylene (XLPE) has been shown to reduce wear and
thereby the onset of osteolysis in total hip arthroplasty. Hip simulator studies have
suggested that while XLPE generates low wear under smooth counterface bearing surfaces,
there appears to be an increased sensitivity to scratched femoral head conditions which can
occur in the patient. However, these simulator studies have not combined damaged articular
surfaces with a severe gait model, representing the worst-case scenario for high-risk, active
patients. This hip simulator study has shown that the size distribution of wear particles
generated in tests on 5 MRads crosslinked polyethylene can be influenced by the degree of
patient activity. Fast jogging showed a greater influence on the number of sub-micron-sized
wear particles (5-fold increase compared to walking) than on volumetric wear rate (26
mm3/106 cycles compared to 29 mm3/106 cycles). Fast jogging also did not generate the
largest wear particles (>I 0p m) produced by normal walking. Roughening of the Co-Cr-Mo
femoral heads created a 1700-fold increase in the numbers of sub-micron PE particles
under fast jogging. The clinical significance of this result suggests that highly active
patients will generate high numbers of bioactive PE wear particles within the accepted
bioactive range, 0.2-10μm.
Metal-on-metal (MOM) hip arthroplasty has also seen rapid growth worldwide. However,
there remains concern over their long-term biocompatibility due to systemic ion release.
Therefore, the aim of this current investigation was to test the hypothesis that larger
diameter MOM bearings (greater than 40 mm) will generate smaller Co-Cr-Mo wear
particles compared to a 28 mm size bearing, and reduce the total wear particle surface area,
and to test the hypothesis that `severe' gait conditions will greatly increase the size of Co-
Cr-Mo wear particles, thereby causing a sizable increase in wear particle surface area.
Walking with a 28 mm bearing produced the largest wear rate of at 0.92 mm3/106 cycles,
whereas the 40 mm and 56 mm bearings, generated lower wear rates of 0.39 mm3/106
cycles and 0.32 mm3/106 cycles respectively. Simulated fast jogging created a 3-fold
increase in the number of elongated (needle) wear particles compared to normal walking,
and generated a 20-fold increase in total wear particle surface area per year of use
compared to normal walking. The clinical significance of this result suggests that highly
active patients with MoM implants will exhibit greater ion release, although this may be
minimised by using larger diameter bearings for active or younger patients.Engineering and Physical Science Research Council (EPSRC)cor grant fundin
Comparison of various high-stress wear conditions and wear performance of martensitic steels
No full text<p>The demanding environments typically encountered by the wear resistant steels create challenges for the materials selection, because the hardness grades of the steels alone do not reveal the true nature of their wear behavior. In this study, five commercial wear resistant steels were tested using three application oriented test methods with five different test variables for abrasion, impact-abrasion, and slurry erosion. All the used test methods produced high-stress conditions that crushed the used mineral abrasive, plastically deformed the sample surfaces, and led to the formation of adiabatic shear bands. When the results produced by the chosen methods were compared, the normalization of the wear losses by the wear area and test time revealed well the differences between the methods. The test methods ranked the steels similarly, but there were clear differences in the wear rates and wear mechanisms between the tests. In addition, the abrasive methods produced surface adiabatic shear bands, while subsurface shear bands were initiated by the more impacting methods. In the studied conditions, the work hardening ability of the steel had a clear influence on its wear resistance, which largely explains the marked differences in the wear rates of the studied commercial 500HB grade steels.</p>Peer reviewe
The evolutionary paradox of tooth wear: simply destruction or inevitable adaptation?
No full textOver the last century, humans from industrialized societies have witnessed a radical increase in some dental diseases. A severe problem concerns the loss of dental materials (enamel and dentine) at the buccal cervical region of the tooth. This “modern-day” pathology, called non-carious cervical lesions (NCCLs), is ubiquitous and worldwide spread, but is very sporadic in modern humans from pre-industrialized societies. Scholars believe that several factors are involved, but the real dynamics behind this pathology are far from being understood. Here we use an engineering approach, finite element analysis (FEA), to suggest that the lack of dental wear, characteristic of industrialized societies, might be a major factor leading to NCCLs. Occlusal loads were applied to high resolution finite element models of lower second premolars (P2) to demonstrate that slightly worn P2s envisage high tensile stresses in the buccal cervical region, but when worn down artificially in the laboratory the pattern of stress distribution changes and the tensile stresses decrease, matching the results obtained in naturally worn P2s. In the modern industrialized world, individuals at advanced ages show very moderate dental wear when compared to past societies, and teeth are exposed to high tensile stresses at the buccal cervical region for decades longer. This is the most likely mechanism explaining enamel loss in the cervical region, and may favor the activity of other disruptive processes such as biocorrosion. Because of the lack of dental abrasion, our masticatory apparatus faces new challenges that can only be understood in an evolutionary perspective
Effect of tempering on the impact-abrasive and abrasive wear resistance of ultra-high strength steels
No full text<p>Tempering is an essential part in the fabrication of ultra-high strength steels and it is also widely applied in the processing of wear-resistant steels. In this paper, the effects of different tempering temperatures on the impact-abrasive and abrasive wear properties of martensitic ultra-high strength steels were studied. A novel press-hardening steel with carbon content of 0.4 wt% was received in hot-rolled condition and further austenitized, water-quenched and tempered for 2 h at different temperatures (150–400 °C). Tensile strength values up to 2200MPa and hardness exceeding 650HV were measured. Wear testing was done with impact-abrasive impeller-tumbler and abrasive dry-pot application-oriented test methods simulating mining and mineral handling environments. A laboratory rolled 600HB steel and a commercial 500HB grade wear-resistant steel were included for comparison. The wear surfaces and cross-sections of the samples were thoroughly characterized. Both testing methods produced highly deformed surface layers and strong work-hardening. Wear performance was mainly controlled by the initial hardness of the steels, but differences were found in the highly work-hardened surfaces of the steels.</p>Peer reviewe
Utility of a fretting device working under free displacement
No full textRelative movements of low amplitudes between two materials in contact are generally reproduced on fretting devices with imposed displacement or imposed tangential force. The damage kinetics observed (cracking, wear) is established under such conditions. In this article, a fretting device working under free displacement is used to characterize the damages generated by seizure and wear. The conditions of seizure are analyzed from the total sliding distance and the discussion is focused on a correlation established with Dupre's work of adhesion. The wear behavior of materials has been characterized from an energetic wear coefficient taking into account the wear volume of contact, the total sliding distance and the dissipated energy
Impact-abrasive and abrasive wear behavior of low carbon steels with a range of hardness-toughness properties
No full textThis work investigates steels for mining wear applications involving abrasive and impact-abrasive conditions. The study comprises four low carbon steels with a range of hardness-toughness combinations: a commercial grade martensitic steel, the same steel heat treated to lower bainite, a commercial TRIP steel (tensile strength grade 700 MPa), and a quenching-partitioning (QP) steel. The <br/>steels were subjected to crushing pin-on-disc (CPOD) and slurry-pot wear tests, offering reasonably high-stress abrasive and impact-abrasive conditions, respectively. The results showed that the best performer in both studied wear conditions is the martensitic steel due to its higher initial hardness. Nevertheless, the performance benefit of this steel was of lesser magnitude in the slurry-pot than in the CPOD tests. On the other hand, the TRIP steel showed poor ranking in the CPOD tests but outperformed the QP and lower bainite steels in the slurry-pot tests. Detailed surface and subsurface wear damage investigations were conducted to study the wear responses of the microstructural constituents of the steels to explain their wear behavior in different wear conditions.Peer reviewe
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