Оценка надежности трибосистем на неустановившихся режимах работы

The directions of the use of the method of acoustic emission (AE) for the study of stationary and transient processes in tribosystems during the operation have been considered here. It has been shown that the application of this method will allow obtaining information about the state of friction surfaces and the rate of wear during transients (running-in) processing online. To substantiate the choice of the informative parameters of AE, the cluster analysis of the frames of AE signals from the friction zone of the tribosystem with the separation of the signal into the groups of the sources of its generation has been performed. The correlation dependence between the friction coefficient fтр and the values of the peak factor of cluster K2, the correlation coefficient r = 0.99, and the rate of volumetric wear I, m3/h, and the values of the peak factor of cluster K3, the correlation coefficient r = 0.99 have been established. The values of the peak factor of cluster K4 correlate with the rate of volumetric wear during the running-in, the correlation coefficient r = 0.98. It has been experimentally confirmed that the cluster analysis of acoustic emission signals from the friction zone of the tribosystem allows one to identify the surface processes during wear, thereby increasing the robustness and information content of the AE method. This analysis can serve as the basis for the development of a diagnostic technique for tribosystems during their operation, which will make it possible to measure the wear rate at any time and calculate the tribosystem resource

Current evidence suggests that loosening of the acetabular socket is related to the volume of ultra-high molecular weight polyethylene wear debris generated at the articulating surfaces, through a process of bone resorption. Therefore it is important that the rate of volumetric wear is minimized in an attempt to extend the useful life of the procedure. Laboratory evidence indicates that a reduction in sliding distance would be beneficial in achieving this target and may be attained by a reduction in femoral head radius. To investigate the relationship between femoral head size and the rates of both volumetric wear and penetration, 200 acetabular components were retrieved at the time of revision surgery. The joints had femoral heads ranging in size from 11.1 to 19.8 mm radius. For those sockets that were loose at revision surgery, a significant correlation was observed, between the rate of volumetric wear and the radius of the femoral head. For this cohort an increase in radius of 1 mm resulted in an increased rate of volumetric wear of 5.1 (SE 1.4) mm3/yr. However, the explained variance in the regression was low and exemplifies the multifactorial nature of the wear process. In particular, it is anticipated that the activity of the patient will have a significant effect on the rate at which the debris is produced. No significant correlation was observed between the rate of linear wear and femoral head radius. These results would indicate a benefit in using head sizes of a smaller radius, which generate debris at a reduced rate, and therefore require more time to accumulate large volumes of wear products.

We evaluated the rates of volumetric wear and the patterns of wear of 128 acetabular components retrieved during an autopsy or a revision operation between one and twenty-one years after total hip arthroplasty. Twenty-two all-polyethylene components were retrieved at autopsy from hips that had been functioning well at the time of death (Group A). The remaining 106 components--eighty-four all-polyethylene components (Group B) and twenty-two metal-backed components (Group C)--were retrieved during revision operations. All 128 components had been inserted with cement. The mean rate of volumetric wear, determined directly with a fluid-displacement method, was thirty-five cubic millimeters per year (range, eight to 116 cubic millimeters per year) for Group A, sixty-two cubic millimeters per year (range, eight to 256 cubic millimeters per year) for Group B, and ninety-four cubic millimeters per year (range, twelve to 284 cubic millimeters per year) for Group C. Multivariate regression analysis showed a significant relationship (p < 0.05) between the size of the femoral head and the calculated mean annual rate of volumetric wear. The rate of volumetric wear was highest in association with thirty-two-millimeter femoral heads and lowest in association with twenty-two-millimeter heads; according to linear regression analysis, this represented a 7.5 per cent increase (Group A) or a 10 per cent increase (Group B) in the rate of wear for every one-millimeter increase in the size of the head. Linear regression analysis also showed a significant relationship between the duration that the implant had been in situ and the rate of wear (p < 0.05), with the rate being highest initially after the operation and decreasing with an increasing duration in situ. With the numbers available, the patient's age and gender and the side of the arthroplasty did not have a significant relationship to the annual rate of volumetric wear. Increased thickness of the polyethylene was related to a decreased rate of wear (p < 0.05) in the group of metal-backed components, which had a 25 per cent increase in the rate of wear for every one-millimeter decrease in thickness, but not in the other groups. The estimated median annual rates of wear, after adjustment of confounding variables to a hypothetical constant set of median values for the parameters (duration in situ, 132 months; diameter of the femoral head, twenty-six millimeters; and thickness of the polyethylene, eight millimeters), were significantly different among the three groups of components (p < 0.05). Histological evaluation of the worn surfaces showed the predominant mechanisms of wear to be abrasion and adhesion rather than fatigue-cracking or delamination. The highly worn areas were polished to a glassy finish on gross examination, but scanning electron microscopy showed numerous multidirectional scratches along with fine, drawn-out fibrils with a diameter of one micrometer or less oriented parallel to each other. These fibrils are the most likely source of submicrometer wear particles. Thus, wear appeared to occur mostly at the surface of the components and to be due to large-strain plastic deformation and orientation of the surface layers into fibrils that subsequently ruptured during multidirectional motion.

Effects of knee simulator control method and radiation dose on UHMWPE wear rate, and relationship between wear rate and clinical revision rate in National Joint Registry

The development of osteolysis, a commonly reported complication after total hip arthroplasty without cement, is perceived to be related to the amount of polyethylene particles generated from the bearing surfaces. Although the literature has suggested that the prevalence of osteolysis increases with increasing rates of polyethylene wear, this relationship has never been quantified. The goals of this study were to quantify the relationship between the prevalence of osteolysis and both linear and volumetric wear and to evaluate the risk of osteolysis as a function of wear in a currently used, porous-coated cup design. Polyethylene wear and osteolysis were examined in fifty-six hips with a Duraloc-100 acetabular cup articulating with a 28-mm femoral head. Penetration of the prosthetic head into the polyethylene liner was measured, with use of a validated computer-assisted technique, from anteroposterior pelvic radiographs of each patient. From these measurements, linear and volumetric wear rates were calculated. Each patient's series of radiographs was examined independently for the presence of osteolysis. A logistic regression analysis was performed to determine the risk of osteolysis associated with a given change in linear or volumetric wear rate. Osteolysis was found in twenty-three of the fifty-six hips. The hips with osteolysis had significantly higher linear (p < 0.001) and volumetric (p = 0.003) wear rates than the hips without osteolysis. Logistic regression revealed that every 0.1-mm/yr increase in the linear wear rate increased the likelihood of the development of osteolysis by a factor of four. Each 40-mm (3) /yr increase in volumetric wear raised the risk of osteolysis by about three times. To our knowledge, this study represents the first time that the relationship between polyethylene wear, as determined by both linear wear and volumetric wear, and the prevalence of osteolysis has been quantified. The use of the linear wear rate as a predictor of osteolysis can be a valuable tool in assessing the longevity of a particular implant. The results of our analysis provide quantitative support to the observation that a wear rate of 0.2 mm/yr seems to represent a "critical threshold" for the development of osteolysis. Close radiographic monitoring with the determination of linear wear rates to assess the risk of osteolysis is recommended for all patients after total hip arthroplasty.

We present the ten-year data of a cohort of patients, aged between 18 and 65 years (mean age 52.7 years; 19 to 64), who underwent total hip arthroplasty. Patients were randomised to be treated with a cobalt-chrome (CoCr) femoral head with an ultra-high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (XLPE) or ceramic-on-ceramic (CoC) bearing surface. A total of 102 hips (91 patients) were randomised into the three groups. At ten years, 97 hips were available for radiological and functional follow-up. Two hips (two patients) had been revised (one with deep infection and one for periprosthetic fracture) and three were lost to follow-up. Radiological analysis was performed using a validated digital assessment programme to give linear, directional and volumetric wear of the two polyethylene groups. There was a significantly reduced rate of steady-state linear wear with XLPE (0.07 mm/yr) compared with UHMWPE (0.37 mm/yr) (p = 0.001). Volumetric wear was also significantly reduced in the XLPE group (29.29 mm3/yr) compared with the UHMWPE group (100.75mm3/yr) (p = 0.0001). There were six patients with UHMWPE who had non-progressive osteolysis and none in the XLPE group. All three bearing groups had significant improvements in 12-item short form health survey scores, Western Ontario and McMaster Universities Osteoarthritis Index score and Harris Hip Score. However, the improvement in HSS was significantly less in the UHMWPE group (p = 0.0188) than in the other two groups. At ten years, the rates of volumetric and linear wear in the XLPE group remain low and predominantly below the estimated threshold for osteolysis (1 mm/yr). The rate of linear wear in the XLPE group was three times less than in the UHMWPE group at five-year follow-up and five times less at ten years. The rate of volumetric wear was also three times less in the XLPE group at ten years. While CoC also performs well, XLPE at ten years remains a safe and excellent bearing option in young patients, with low rates of wear and no evidence of osteolysis. Cite this article: Bone Joint J 2017;99-B:1590-5.

Low Wear at 10-Year Follow-Up of a Second-Generation Highly Cross-Linked Polyethylene in Total Hip Arthroplasty.

The objective of this paper is to assess the correlation of volumetric tool wear (VTW) and wear rate of carbide tools on the material removal rate (MRR) of titanium alloys. A previously developed methodology for assessing the worn tool material volume is utilized for quantifying the VTW of carbide tools when machining Ti-6Al-4V. To capture the tool substrate response, controlled milling experiments are conducted at suitable corner points of the feed-speed design space for constant stock material removal volumes. For each case, the tool material volumes worn away, as well as the corresponding volumetric wear profile evolution in terms of a set of geometric coefficients are quantified — these are then related to the MRR. Further, the volumetric wear rate and the M-ratio (volume of stock removed to VTW), which is a measure of the cutting tool efficiency, are related to the MRR — these provide a tool-centered optimal MRR in terms of profitability. This work not only elevates tool wear from a 1-D to 3-D concept, but helps in assessing machining economics from a stock material removal efficiency perspective as well.

The objective of this paper is to assess the correlation of volumetric tool wear (VTW) and wear rate of carbide tools on the material removal rate (MRR) of titanium alloys. A previously developed methodology for assessing the worn tool material volume is utilized for quantifying the VTW of carbide tools when machining Ti–6Al–4V. To capture the tool response, controlled milling experiments are conducted at suitable corner points of the recommended feed-speed design space, for constant stock material removal volumes. For each case, the tool material volume worn away, as well as the corresponding volumetric wear profile evolution in terms of a set of geometric coefficients, is quantified—these are then related to the MRR. Further, the volumetric wear rate and the M-ratio (volume of stock removed to VTW) which is a measure of the cutting tool efficiency, are related to the MRR—these provide a tool-life based optimal MRR for profitability. This work not only elevates tool wear from a 1D to 3D concept, but helps in assessing machining economics from a stock material-removal-efficiency perspective as well.

Ultra-high-molecular weight polyethylene wear: An in vitro comparison of acetabular metal types and polished surfaces

Sequentially Irradiated and Annealed Highly Cross-Linked Polyethylene: Linear Vector and Volumetric Wear in Total Hip Arthroplasty at 10 Years

Wear Rates With Large Metal and Ceramic Heads on a Second Generation Highly Cross-Linked Polyethylene at Mean 6-Year Follow-Up

Total hip arthroplasty (THA) is the 2nd most common total joint replacement surgery in the United States. However, not all THA devices perform well and need revised for several reasons including dislocation. Higher offset acetabular liners reduce this problem by creating a more anatomically/biomechanically natural hip joint, increasing soft-tissue tension, and accommodating larger femoral heads in smaller acetabular cups via increased polyethylene thickness. To our knowledge, however, in vivo wear (another failure mode) performance of offset acetabular liners remains unknown. 2 cohorts of 40 individuals (0-mm, 4-mm offset acetabular liners, respectively) from a single surgeon's consecutive caseload were assessed. 6-week/5-year post-op radiographs were compared using a validated method using SolidWorks software to assess in vivo linear and volumetric wear rates. Resultant surgical offset was also quantified using this method. Linear wear rate for 0-mm and 4-mm offset cohorts were 0.01 ± 0.09 mm/year and 0.08 ± 0.12 mm/year, respectively. Volumetric wear rate for 0-mm and 4-mm offset cohorts were 30.4 ± 20.4 mm3/year and 61.6 ± 42.1 mm3/year, respectively. Both of these were statistically significant. Neither linear nor volumetric wear rate was correlated with resultant surgical offset. To our knowledge, this is the 1st study to compare in vivo wear performance of 0-mm and 4-mm offset acetabular liners. Although linear and volumetric wear rates were different between cohorts, neither reached previously established osteolysis thresholds. Moreover, wear rates were not correlated with resultant surgical offset. Finally, no patients in either cohort showed signs of osteolysis nor needed revision. As such, the clinical relevance of the wear rate differences is potentially less significant.

Activity level and wear in total knee arthroplasty: A study of autopsy retrieved specimens

Similar wear rates of 1st and 2nd generation highly cross-linked polyethylene in primary total hip arthroplasty in patients less than 30 years of age: A minimum 5-year follow-up.