Jacob Sukumaran

Dynamic mechanical and thermogravimetric analysis of PTFE blended tailor-made textile woven basalt–vinyl ester composites

In this work, the authors prepared basalt–vinyl ester tailor-made green composites with uncoated and polytetrafluroethylene coated basalt woven fabric. These composites were subjected to dynamic composites-made mechanical analysis and thermo gravimetric analysis. Results revealed that a significant improvement of 18%, 14% and 13% was observed for storage and loss modulus and damping properties of polytetrafluroethylene-coated composite at low temperature region. The thermo gravimetric analysis results indicated a three-stage degradation for the polytetrafluroethylene-filled composites. Based on the acceptability from the literature, the tribo-test was performed only on the polytetrafluroethylene-coated composite for the selected PV limit of 400 MPa-mm/s (10 KN and 50 mm/s) in a flat-on-flat configuration. It was found that the influence of polytetrafluroethylene filler on the static and dynamic coefficient of friction and specific wear rate of the composite was more pronounced at dry wear test condition and it was found as 0.22, 0.12, and 4.87484 E-09, respectively. However, the results of improved storage and loss modulus and damping manifested negative correlation with the friction characteristics in the glassy region. Further, the SEM-coupled EDX spectral analysis was performed to understand the formation of transfer layer in counter surface. This polytetrafluroethylene blended composite is to be considered as an alternative to the bearing materials in offshore application.

A review on tribological properties of natural fiber based sustainable hybrid composite

Natural fibers based composites having good mechanical properties have attracted tribologists to explore their application range from friction materials to friction modifiers. Hybridization of the fiber reinforced polymer composite is necessary to ensure combined mechanical strength and tribological properties. Hence, this review discusses “hybrid natural fiber composites” in detail. Earlier, reports listed the tribological failure in polymer composites from the view point of mechanical failures such as fiber/matrix interfacial debonding, matrix crack, fiber fragments, and debris generation. The present review focuses on the transfer layer formation, influence of contact temperature, and degradation of self-lubricating polymer behavior of natural fiber based hybrid composites. The authors assume that present review article on the tribological properties of hybrid composites can guide the research community towards innovative material design for tribological applications by the hybridization of natural fiber composites.

Correction, stitching and blur estimation of micro-graphs obtained at high speed

Micro-structures of surface are considered to be effective in identifying the damage mechanisms. The industry uses computer vision to auto detect misalignment of the components as it is a contactless tool. However, in scientific investigations micro structures obtained online at high-speed has to be analyzed. In this work the change detection of a specimen rotating at a high speed studied online using image processing techniques in micro graphs which provides a clear insight about the dimensional changes. The specimen under study is made from polymer composite which has contact with a steel wheel and rotates at a high speed. The blur as a measure of dimensional change of the polymer composite can be identified due to the change in focus. The micro-structure images were dark and span a very small region of the surface due to high speed image acquisition, short shutter time and magnification of the microscope. Thus, pre-processing procedures like image enhancement, stitching and registration are performed. Then 15 blur estimation methods are applied to the stitched images. The results of three methods present a good correlation with dimensional change provided by a stylus instrument.

Effect on Friction for Different Parameters in Roll–Slip of Polyamide–Steel Nonconformal Contacts

Standards for tribological testing focus mainly on sliding, but in applications like gears, rollers, etc., rolling appears together with sliding, resulting in roll–slip situations. In this study, the roll–slip behavior of polymer materials was tested using a twin-disc experimental test setup. Three different loads of 61 N (13 MPa), 110 N (18 MPa), and 161 N (22 MPa) together with five different speeds ranging from 10 to 700 rpm were used for a slip ratio of 15%. Two different counter materials were used: tool steel (M238) and nonalloyed structural steel (S335). Both of the counter materials showed a friction behavior that was almost linear to the increase in load for high speeds at 700 rpm. But at speeds below 200 rpm the tool steel showed an exponential behavior. At low loads (61 and 110 N) there was an exponential increase in friction force that became more linear after 110 N. From a velocity point of view both of the counter materials showed similar friction behavior with a different value in friction force. By comparing the behavior for both of the counter materials against polyamide 6, the tool steel showed an increased friction force that makes the nonalloyed structural steel a more suitable counter material for polyamide.

Finite Element Model in Abrasion Analysis for Single-Asperity Scratch Test

Abrasion is one of the dominant source for the damage of soil engaging tools such as tines, ploughshares, separators etc. Since the conventional abrasion analysis relies on the posterior groove-ridge investigation from the worn surface profile, this study presents a numerical approach to predict the abrasive wear behaviors including the micro-cutting and micro-ploughing. A Finite Element Model (FEM) has been developed to identify these mechanisms. Modeling techniques representing local plastic deformation from micro-ploughing and material removal from micro-cutting were implemented. A comparison between basic von Mises plasticity model and a strain-based damage model namely Modified Bai Wierzbicki (MBW) was discussed. The material characterization and its model calibration were included. The groove-ridge ratio from single-asperity scratch test experimental results were used as a benchmark parameter.

Extruded and Injection Moulded Virgin PA 6/6 as Abrasion Resistant Material

Polyamide (PA6/6) is often used as a tribological pair in abrasion prevalent applications such as hinges and sliders. PA6/6 is frequently processed by injection moulding and extrusion process. It is known that these processes influence the polymers mechanical behaviour, but their influence on the polymers wear response has not been studied. Hence the present research attempts to study the influence of different manufacturing processes on tribological behaviour for PA6/6. Wear tests were performed on a pin abrading tester (DIN 50322). Abrasion resistance of both extruded and injection moulded PA6/6 were tested at different loads (20 and 35 N). Single-pass (nonoverlapping mode) and multipass testing (overlapping mode) were used to understand the influence of clogging of wear debris. It is evidenced that with increasing load the specific wear rate decreases; moreover, fine abrasives tend to reduce the wear rate. In multipass testing a transfer layer clogged on the counterface that acted as a protective agent and lowers wear rate. Poor mechanical strength of injection moulded polymers is apparently compensated by microstructural response for having a similar wear behaviour between extruded and injection moulded PA 6/6. Hence a proper balance between microstructural and mechanical characteristics is an absolute must in PA 6/6 for better wear performance.

Online Wear Detection Using High-Speed Imaging.

In this paper, the change detection of a fast turning specimen is studied at micro-level, whereas the images are acquired without stopping the rotation. In the beginning of the experiment, the imaging system is focused on the surface of the specimen. By starting the rotation of the specimen, the diameter of the specimen changes due to wear, which results in de-focusing of the imaging system. So the amount of blur in the images can be used as evidence of the wear phenomenon. Due to the properties of the microscope, the corners of the frames were dark and had to be cropped. So, each micrograph reflects only a small area of the surface. Nevertheless, techniques like stitching of multiple images can provide a significant surface area for micro-level investigation which increases the effectiveness of analyzing the material modification. Based on the results computer vision could detect a change of about 1.2 µm in the diameter of the specimen. More important is that we could follow the same locations of the surface in the microscopic images despite blurring, uneven illumination, change on the surface, and relatively a high-speed rotation.

How hardmetals react to wear: Nano is not always the best

Hardmetal PM specialists are coming to realise the importance of microstructure in terms of the development of useful industrial materials and the tooling that is made from them…