Numerical simulation of sliding wear for a polymer–polymer sliding contact in an automotive application

Injection moulded polymer-based components are important for cost effective and fast production/assembly of auxiliary mechanisms in automotive industry. Wear is one of the critical factors, which influences the reliability and useful life in such mechanical components. Experimental determination of life parameters in terms of wear has both a cost and time impact. Therefore, the ability to predict wear at the development stage enables the designers to come up with a better design, longer useful life and more reliable products. This paper presents a numerical simulation of wear for a polymer–polymer sliding surface contact in dry conditions. Finite element analysis (FEA) is used as a tool to calculate nodal pressures at the contact area for small sliding steps. These pressures are then inputted to a customized wear calculating routine. The routine uses averaged wear coefficients (wear rates) obtained from custom designed experiments. The FE contact geometry is modified after each sliding step to account for the contact height decay thus determining wear volume loss over usage time and predicting the worn geometry.     

Influence of rigid and frictional kinematic linkages in tool–workpiece contact on the uniformity of tool wear

The motion of the machined part over the tool’s working surface is considered in raster finishing with frictional kinematic linkage. The relative trajectories of the part and tool are analyzed. In forward movement of the lap, rigid kinematic linkage in the part–tool contact is recommended.     

Finite element study for determination of material’s creep parameters from small punch test

Compared with the conventional tensile creep test, it is much more difficult to obtain the creep properties of a material by the small punch creep test due to the complex deformation response and stress distribution in the miniature specimen of the material. Although creep behavior has been investigated by the small punch test, most studies have been limited to a specimen geometry and therefore, cannot be extended to other conditions conveniently. In this study, a new developed analysis routine is presented to derive the creep parameters of a material using data obtained from the small punch creep test. With the aid of the finite element method, the displacement and the displacement rate of the small punch are obtained for different load levels. The relationship between the stress and creep strain of the specimen and the applied load and the punch displacement is obtained by a dimensional analysis and the membrane stretching model. The creep properties obtained from small punch tests and the conventional creep tests are also compared. The values of the creep properties between the two types of tests agree well with each other within an acceptable accuracy range. This indicates that it is possible to obtain the creep parameters of a material from the small punch creep test instead of the conventional creep test by the analysis routines proposed in this study. Some suggestions for data reduction of the small punch creep tests are also presented to obtain more accurate material creep parameters.     

Influence of tilt angle of plate on friction and transfer layer—A study of aluminium pin sliding against steel plate

In the present investigation, unidirectional grinding marks were attained on the steel plates. Then aluminium (Al) pins were slid at 0.2°, 0.6°, 1.0°, 1.4°, 1.8°, 2.2° and 2.6° tilt angles of the plate with the grinding marks perpendicular and parallel to the sliding direction under both dry and lubricated conditions using a pin-on-plate inclined sliding tester to understand the influence of tilt angle and grinding marks direction of the plate on coefficient of friction and transfer layer formation. It was observed that the transfer layer formation and the coefficient of friction depend primarily on the grinding marks direction of the harder mating surface. Stick-slip phenomenon was observed only under lubricated conditions. For the case of pins slid perpendicular to the unidirectional grinding marks stick-slip phenomenon was observed for tilt angles exceeding 0.6°, the amplitude of which increases with increasing tilt angles. However, for the case of the pins slid parallel to the unidirectional grinding marks the stick-slip phenomena was observed for angles exceeding 2.2°, the amplitude of which also increases with increasing tilt angle. The presence of stick-slip phenomena under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities.     

Development of a tool–work thermocouple calibration system with physical compensation to study the influence of tool-holder material on cutting temperature in machining

The main objective of this work is the experimental investigation of the influence of tool-holder material on tool–chip interface temperature and on the surface temperatures of the cutting tool and tool-holder. The study was conducted in dry machining of grey iron with uncoated cemented carbide inserts, using identical cutting parameters. Five tool-holders were made with materials having different thermal conductivity: copper, brass, aluminium, stainless steel and titanium alloy. The tool-holders are identical and have the same constructive aspects obtained from the commercial tool-holder for machining grey iron. The temperature at the tool–chip interface was measured using the tool–work thermocouple method and the surface temperatures on the insert and tool-holders, by conventional T type thermocouples. The system was modified in order to develop an experimental procedure for the physical compensation of the secondary junctions and parasite thermoelectric e.m.f. signals. Also, modifications were carried out in a conventional tail-stock to obtain the e.m.f. signal between the rotating workpiece and the stationary insert, without significantly altering the stiffness of the system. The tail-stock with mercury bearing inside was insulated electrically. The internal connections became reference junctions at room temperature; otherwise, they would act as secondary junctions. The calibration of the tool–work thermocouple was developed in the experimental apparatus using the same modifications as implemented in the system. Besides the results obtained with the investigation of the effects of the tool-holder materials on the surface temperatures of the insert and the tool-holder and the tool–chip interface temperature, this research presents also contributions to the calibration and performance of the tool–work thermocouple method with physical compensation.     

Influence of tool geometry on the stress–strain state of pipe in expansion by a shaped draw bar

The expansion of shaped pipe in oilfield borehole repair by means of various shaped draw bars is modeled by the finite-element method. The optimal draw-bar configuration is determined from the pressure on the tool and the effective strain. Recommendations are made regarding the shape of the draw bar.     

A comparative study of the tool–chip contact length in turning of two engineering alloys for a wide range of cutting speeds

Tool chip contact length is an important parameter in machining, as it provides an indication of the size of area of interaction between the hot chip and the tool surface and hence the interface heat transfer zone. Heat transfer and thermally activated wear modes usually dominate tool wear in the high speed machining of steels and machining of titanium alloys at most cutting speeds. In this study, existing models for the prediction of tool–chip contact length are reviewed and examined for their suitability in high speed machining of two widely used engineering alloys. Orthogonal turning tests for AISI 1045 steel and Ti6Al4V titanium alloy are conducted for a range of cutting speeds from conventional to high speeds. New contact length models are presented for both materials covering a wide range of cutting speeds. More significantly, these contact length models are appropriate for high speed machining where thermal loads significantly influence process performance. Additionally, the work discusses how the machinability of engineering materials influences the ability to predict contact length.     

Dynamics and stability – A proposal for related terms in Metrology from a mathematical point of view

We describe measurement quantities and measurement processes verbally by using everyday terms, often sanctioned by international standards and guides. However, we apply some of these terms inconsistently as compared to definitions in base sciences like Logic and Mathematics, Signal and System Theory, Stochastics and Statistics, Estimation and Optimisation Theory. This is especially true for a group of terms in Metrology, namely for the terms kinetic, static, time dependent, time invariant, stable, stationary, drifting etc., which all populate the general environment of the main term dynamics. The paper explores systematic relations between these and similar terms and discusses the aptitude of their implementation in everyday practice. Cardinal point is the term dynamic, which will be investigated thoroughly. So, derived terms can be defined, incorporated and judged accordingly. For the field of Metrology some new and, maybe, surprising results arise, worth being considered in the near future.     

Determination of the significant anthropometry dimensions for user-friendly designs of domestic furniture and appliances – Experience from a study in Malaysia

Future design for the elderly is undoubtedly important for their survival to live independently in this challenging world. Therefore to realize the mentioned design, an anthropometric database for Malaysian elderly population need to be developed. A total of 107 participants took part in the study which involved 61 females and 46 males with ages ranging between 55 and 70 years. An earlier anthropometric database for Malaysian elderly population has been developed. Sixty body dimensions were measured in the study. It is hoped that from this study, the database can be used as a guideline in designing household facilities for the Malaysian elderly and elderly of other countries. The design of the household facilities should be influenced by sound ergonomics dimensions in order to create a safe and healthy environment for the elderly.