Friction and wear of polyetheretherketone (PEEK) samples with different melt flow indices

Polyetheretherketone (PEEK) is a promising polymer material for tribological applications. Friction and wear tests of PEEK samples vs. steel with different melt flow indexes (MFI) were studied. The results showed dependencies of the friction force on the sliding velocity, either decreasing or increasing depending on whether the normal load exceeds the yield strength of the polymer. The data can be well fitted with the assumption of the two-component friction law involving the Amontons component and an adhesional component. With a decrease in MFI, i.e. with an increase in viscosity of polymer. The adhesive component of friction increases with increasing viscosity while the abrasive wear decreases. At high loads, the plastic displacement increases with an increase in the viscosity and plasticity of the polymer. The wear does not show a clear correlation with the viscosity.

Macroplastic Debris Transfer in Rivers: A Travel Distance Approach

Plastic accumulation in the marine environment is a major concern given the harmful effects and longevity of plastics at sea. Although rivers are likely to significantly contribute to the flux of plastic to marine systems, the behaviour of plastic debris in fluvial systems remains poorly understood and estimates of riverine plastic flux derived from field measurements and modelling efforts are highly uncertain. This paper presents a new probabilistic model of plastic transport in rivers which describes the main processes controlling plastic displacement and which predicts the statistical distribution of travel distances for individual items of buoyant macroplastic debris. Macroplastic transport is controlled by retention in temporary stores (or traps) created by vegetation, bank roughness elements and other obstacles. The behaviour of these traps is represented in the model via a series of Bernoulli trials conducted in a Monte Carlo simulation framework. The model was applied to a tracer experiment in a small 1.1 km river reach. Three replicates were used for calibration and three for validation. For each replicate, 90 closed air-filled polyethylene terephthalate (PET) bottles were introduced at the upstream end of the reach and the location of each bottle was recorded after 24 h. Bottles were chosen as “model” macroplastic litter items given their high usage and littering rate. Travel distances were low. The average and maximum distances travelled over 24 h were 231 m and 1.1 km, respectively. They were also variable. The coefficient of variation of travel distances was 0.94. Spatial patterns were controlled by the location and characteristics of discrete traps. The model was able to describe the observed travel distance distributions reasonably well, suggesting that modelling plastic behaviour in longer reaches and even whole catchments using a stochastic travel distance approach is feasible. The approach has the potential to improve estimates of river plastic flux, although significant knowledge gaps remain (e.g., the rate and location of plastic supply to river systems, the transport behaviours of different types of plastic debris and trap effectiveness in different types of river system, season, and discharge).

Optimized Design of Various Ag Decorated Sn-xAg-Cu0.7 Solder Bump on Cycling Fatigue Reliability for Wafer-Level Chip Scale Packaging

Effects of Ag content (0 ~ 3 wt.%) in Sn-xAgCu0.7 solders on microstructure characteristics and low cycling fatigue at different temperature conditions are overall investigated. To increase Ag content, the solidus point 228.8 ? of Sn-Cu0.7 gradually decreases to 218.5 ? and temperature range of solid-liquid coexistence phase is also decrease. The Sn-Cu0.7 matrix consisted of small particles of Cu6Sn5 within ß-Sn equiaxial grains and did not significantly influence solder hardness. Moreover, much intermetallic compound of plate-like Ag3Sn and rod-like Cu6Sn5 existed in Sn-xAgCu0.7 solders enables to enhance the hardness due to dense network of Ag3Sn precipitation and near eutectic point. As a result of plastic displacement decreases with higher Ag additions, better fatigue lifetime could be achieved at Ag content to 1.5 wt.%. Besides, crack stemmed from thicker IMC layer in Sn-3.0Ag-Cu0.7 solder interface will decrease fatigue performance especially for 80 ? and 120 ?.

Simulation-Based Methodology for Determining the Dynamic Strength of Tire Inflation Restraining Devices

The article suggests and supports a simulation-based methodology for determining whether the dynamic strength of tire inflation restraining devices for tire inflation meet quality requirements and ensure operator safety during a potential tire explosion. Dynamic strength tests using an NM-600 safety shield and NK-0728 safety cage during a 29.5 R25X tire explosion at a pressure of 10 bar were presented as an example application of this methodology. The shield was subjected to destructive tests involving the use of a 2200 kg impactor, dropping it so that the minimum kinetic energy reached 20 kJ at the time of impact. Analyzed devices were constructed of S355 steel in accordance with EN 10025. The Cowper–Symonds model of material for strain rate phenomena was used in the calculations. Simulations of a 20 kJ ring impact against the cage were performed. The equivalent stress distribution was determined, and displacement contour lines for the maximum dynamic deformation value and plastic deformation were calculated. The plastic displacement obtained in numerical tests was equal to the permanent deformation recorded in the experimental test. Further, the simulations showed that the examined cage met the assumed strength criteria. The conducted tests confirmed the usefulness of the proposed methodology for assessing the dynamic strength of safety cages and shields for tire inflation. The full-scale, physical cage testing is difficult to implement because it requires placing a ring impacting the cage wall. This is a major boundary for closed cages, as considered in this publication. Thus, simulation-based methods are becoming a principal tool for safety assessment of tire inflation restraining devices.

EFFECT OF WELDING POSITION ON THE MECHANICAL PERFORMANCE OF MANUAL METAL ARC WELDELD JOINTS VIA ANALYSIS OF VARIANCE

Positional welding is a common challenge in many manufacturing practices and the welding position can affect the mechanical properties of welded joints during manual metal arc welding. This work uses tensile tests to investigate the mechanical properties of welded joints, aiming to test the hypothesis of the influence of welding position on tensile strength, total displacement before rupture and plastic displacement before rupture. This hypothesis was tested for three different coated electrodes (AWS E6010, AWS E6013 and AWS E7018) and three welding positions (1G, 3G and 4G), accounting for nine types of specimens. For each type of specimen, ten repetitions were carried out. Analysis of Variance (ANOVA) was used to test the hypotheses. The welded joints using the welding position 1G presented higher rupture load and larger total displacement before rupture than the other positions.

Statistical model of metal removal removed from product surface under the influence of abrasive particle flow

A model is proposed that describes the forming processes of metal volume removed from the product surface during processing with a free abrasive flow, taking into account the random nature of abrasive particle impact on the surface and the possibility of implementing acts of elastic and plastic displacement of material or micro-cutting.

Estimation Accuracy of Absolute Maximum Elasto-Plastic Displacements of MDOF Oscillators Based on a Modal Combination Rule With Post-Yielding Modal Properties and Linear Response Spectrum Values

Taniguchi, et al. [1] developed an analytical method for evaluating the absolute maximum elasto-plastic displacements of multi-degree-of-freedom (MDOF) oscillators under the action of base excitation based on a modal combination. Its essence is that 1) modal frequencies, shapes and damping during yielding of any member of the MDOF oscillators are readily specified by the modal analysis with the secondary stiffness of the members being yielded, 2) assuming that a bilinear hysteresis may describe the force-displacement relationship of each mode, an equivalently linearized system consisting of a single-degree-of-freedom (SDOF) oscillator is introduced to approximate the absolute maximum elasto-plastic displacement of each mode, 3) the absolute maximum elasto-plastic displacement of the MDOF oscillator is evaluated by the Square Root of Sum of Squares rule (SRSS-rule) by combining the maximum elasto-plastic displacement of each mode approximated by the proposed equivalently linearized system. This study first provides small modification in the equivalently linearized system. Then, employing a couple of MDOF oscillators whose spring at arbitrary storey may yield and an accelerogram, the maximum elasto-plastic displacement of the MDOF oscillator is calculated by the proposed method and is compared with that computed by the time history analysis. Their comparison suggests that the proposed method can reasonably evaluate the absolute maximum elasto-plastic displacement of the MDOF oscillator subjected to earthquake excitation as the conventional SRSS-rule does that for the linear MDOF oscillators.

FEM Contact Stress Analysis at the Bearing Surfaces in Bolted Joints Under External Loadings

The higher bolt preload is better for increasing the integrity of bolted joints. However, the bearing surface could be permanently deformed with too much high preload and the bolt preload decreases with permanent deformation. Thus, an upper limit of bolt preload per contact area at the bearing surfaces, which is called as the critical contact stress, must be examined for various materials of clamped parts. In the previous research, the critical contact stresses were obtained by compressing a cylindrical bar. However, the contact stress distribution of compressing a cylindrical bar is much different to that of an actual bolted joint. In addition, a lot of previous researches used the stress-strain curves under tensile loadings for analyzing the contact stress distributions at the bearing surfaces. In this study, the Finite Element Method is used for contact stress analysis at the bearing surfaces in clamped bolted joints under external loading. Various materials for clamped part are chosen such as steel, aluminum alloy, cast iron and stainless steel. Firstly, the stress-strain curves for the above materials were measured under compressive loadings. The differences in the stress-strain curves under tensile and compressive loadings are evaluated with the above materials. Next, using actual bolts, the displacements at the bearing surfaces in cylindrical clamped parts consisting of the above materials were measured. Finally, elasto-plastic FEM contact stress analyses are carried out for analyzing the plastic displacements at the bearing surfaces under compressive loadings. The mean displacement at the bearing surfaces are compared with those obtained from the experiments for each material. The FEM results of the relationship between the contact stress and the plastic displacement at the bearing surface are in a fairy good agreement with the experimental results for each clamped material. In addition, the critical contact stress at the bearing surface is discussed for each material. Two proposals for the critical contact stress at the bearing surface are described and compared with the critical contact stress of VDI2230.

Experimental Study on Load-Displacement Relationship of Prestressed Cable in Red Clay Stratum

The P-S curves of prestressed anchor cable are obtained by field pull-out tests in the red-clay stratum in Guiyang area. The P-S curves of different theoretical models are discussed base on the theoretical analysis. The elastic and plastic displacement of prestressed anchor cable are analyzed. The results shows that, the anchoring effect are mainly effected by the red-clay mechanic properties in the red-clay stratum; the P-S curve of anchor bolt can be fitted well by the exponential model and conformed to the actual; the plastic displacement is used to anchor’s damage index are more truthfulness in the red-clay stratum.