Temperature‐dependent uniaxial ratchetting of ultra‐high molecular weight polyethylene

Uniaxial stress‐controlled cyclic tests were performed on the ultra‐high molecular weight polyethylene (UHMWPE) polymer at different temperatures. The effects of stress level, stress rate, peak/valley stress hold and loading history on the ratchetting of the UHMWPE were discussed at different temperatures, and the temperature‐dependence of ratchetting was addressed. It is concluded from the experimental observations that the ratchetting of the UHMWPE depends greatly on the test temperature, and the ratchetting strain increases with the increasing temperature from ?20 to 37 °C, but decreases when the temperature is equal to or higher than 60 °C in some cases. The ratchetting is also time‐dependent and increases with the increase of peak stress hold time and the decrease of stress rate. The ratchetting presents apparent loading history dependence, and previous cyclic history with higher stress level remarkably restrains the occurrence of ratchetting in the subsequent cyclic loading cases with lower stress levels, but previous cyclic history with lower stress level hardly influences the ratchetting in the subsequent cyclic loading cases with higher stress levels.     

超高分子量聚乙烯/金属复合材料的摩擦磨损性能

用MM-200型摩擦磨损试验机研究了Ag、Cu、Co、Cr、Fe、Mo、W、Ni、Zn、Pb、Sn、Al等金属粉末填充超高分子量聚乙烯(UHMWPE)复合材料的摩擦磨损性能,利用扫描电子显微镜观察了复合材料磨损表面形貌.结果表明:在低速条件下,金属填料可降低UHMWPE复合材料的摩擦系数;在高速条件下,金属填料对UHMWPE复合材料的摩擦系数影响不尽相同.Ag、Cu、Co、Cr、Fe、Mo、W、Ni、Zn、Pb等金属填料可使UHMWPE的耐磨性显著提高, 而Sn、Al导致UHMWPE的磨损率增大;Ag的减摩抗磨效果最佳.     

电子束辐照对UNMWPE树脂结构和力学性能的影响

研究了电子束辐照超高分子量聚乙烯(UHMWPE)树脂的交联现象,探讨了不同电子束辐照吸收剂量对UHMW-PE的微观结构、力学性能和溶胀度的影响。结果表明,辐照UHMWPE的最大拉伸强度、结晶度和交联度都随着吸收剂量的增大先增大后减小,分别在10kGy、50kGy和100kGy时达到最大值47.3MPa、54.4%和1.66×10-4mol/cm3;溶胀度(SR)和交联网链平均分子量(Mc)随吸收剂量增大先减小后变大;断裂伸长率随吸收剂量的增加而变小。     

Tribological properties of ultra‐high molecular weight polyethylene (UHMWPE) filled with copper micro‐powder

This paper investigates the tribological properties of ultra‐high molecular weight polyethylene (UHMWPE) filled with copper micro‐powder (CMP). The fabrication and testing procedures implemented to characterize strength and wear properties of the composite are discussed. The effect of copper micro‐powder concentration on tensile strength, elongation at break, impact resistance, coefficient of friction, and wear resistance of the composite is investigated. Results show that copper micro‐powder concentration of 1 wt% yields the optimal combination of wear resistance and tensile strength of the composite. A morphological analysis based on scanning electron microscope (SEM) images of the copper micro‐powder‐ultra‐high molecular weight polyethylene specimens is also discussed. The presence of ridges and plaques on the specimens, analyzed after the sliding wear tests, is attributed to fatigue and adhesion mechanisms. Investigations performed by using an electron probe micro‐analyzer provide evidence that the detachment of copper micro‐powder particles from the matrix during sliding wear tests creates a lubricating layer that drastically decreases the coefficient of friction of the composite and improves its wear resistance properties.     

Clinical praxis for assessment of dry weight in Sweden and Denmark: A mixed‐methods study

Overhydration is an independent predictor of mortality in hemodialysis (HD) patients. More than 30% of HD patients are overhydrated, motivating the development of new methods for assessing hydration status. This study surveyed clinical praxis and local guidelines for dry weight (DW) assessment in Swedish and Danish HD units, and examined if differences in routines and utilization of bioimpedance spectroscopy (BIS) and other assistive technology affected frequency of DW adjustments and blood pressure (BP) levels. Cross‐sectional information on praxis, guidelines and routines, plus treatment‐related data from 99 stratified patients were collected. Qualitative data were analyzed with content analysis and interpreted in convergence with statistical analysis of quantitative data in a mixed‐methods design. Local guidelines concerning DW existed in 54% of the units. A BIS device was present in 52%, but only half of those units used it regularly, and no correlations to frequency of DW adjustments or BP were found. HD nurses were authorized to adjust DW in 60% of the units; in these units, the frequency of DW adjustments was 1.6 times higher and systolic BP pre‐HD 8 mmHg lower. There is a wide variation in routines for DW determination, and there are indications that authorization of HD nurses to adjust DW may improve DW assessment. BIS is sparsely used; its implementation may have been delayed by uncertainty over how to manage the device and interpret measurements. Hence, better methods and guidelines for assessing DW and using BIS need to be developed.     

Metal-organic framework derived hexagonal layered cobalt oxides with {1 1 2} facets and rich oxygen vacancies: High efficiency catalysts for total oxidation of propane

A cobalt-based metal–organic framework was used as a precursor to synthesize Co₃O₄ catalysts exhibiting a hexagonal layered morphology by calcination at varying temperatures. Various characterization techniques, such as XRD, SEM, Raman, H₂-TPR, O₂-TPD and N₂ adsorption–desorption, were used to study the effects of calcination temperature on the grain size, surface area, and pore volume of the catalysts. The Co₃O₄ catalyst obtained by calcination at 350 °C (Co₃O₄-350) exhibited the highest catalytic activity for the total oxidation of propane. Furthermore, the small grain size and layered structure of Co₃O₄-350 allowed it to possess a high specific surface area, a highly exposed {1 1 2} facets, and abundant oxygen defects that facilitated a favorable low-temperature reducibility and oxygen mobility, thereby improving catalytic activity. This research offers a simple strategy for synthesis of Co₃O₄ with layered structure, highly exposed {1 1 2} facets and rich oxygen defects.     

Advances in metals and alloys for joint replacement

Metals, ceramics, polymers, and composites have been employed in joint arthroplasty with ever increasing success since the 1960s. New materials to repair or replace human skeletal joints (e.g. hip, knee, shoulder, ankle, fingers) are being introduced as materials scientists and engineers develop better understanding of the limitations of current joint replacement technologies. Advances in the processing and properties of all classes of materials are providing superior solutions for human health. However, as the average age of patients for joint replacement surgery decreases and the average lifespans of men and women increases worldwide, the demands upon the joint materials are growing. This article focuses solely on advances in metals, highlighting the current and emerging technologies in metals processing, metal surface treatment, and integration of metals into hybrid materials systems. The needed improvements in key properties such as wear, corrosion, and fatigue resistance are discussed in terms of the enhanced microstructures that can be achieved through advanced surface and bulk metal treatments. Finally, far reaching horizons in metals science that may further increase the effectiveness of total joint replacement solutions are outlined.