A Simple Semi-Analytic Contact Mechanical Model for Tangential and Torsional Fretting Wear of Axisymmetric Contacts

Fretting wear of axisymmetric contacts is considered within the framework of the Hertz–Mindlin approximation and the Archard law for the linear wear. If the characteristic time scale for the wear is much larger than the duration of a single fretting oscillation, the profile change due to wear during one fretting cycle can be neglected for the contact problem as a zero-order approximation. This allows to give an exact contact solution during each fretting cycle, depending on the current worn profile, and thus for the explicit statement of an ordinary integro-differential equation system for the time-evolution of the fretting profile, which can be easily solved numerically. The proposed method gives the same results as a known, contact mechanically more rigorous simulation procedure that also operates within the framework of the Hertz–Mindlin approximation, but works significantly faster than the latter one. Tangential and torsional fretting wear are considered in detail. A comparison of the numerical prediction for the evolution of the worn profile in partial slip torsional fretting of a rubber ball on abrasive paper shows good agreement with experimental results from the literature.

Analisis Kekasaran Permukaan Besi ASTM36 dengan menggunakan Surftest dan Image –J

Kekasaran permukaan logam merupakan salah satu parameter yang dapat dijadikan acuan dalam penilaian mutu suatu logam. Nilai kekasaran permukaan suatu bahan logam dapat dilakukan dengan pendekatan matematik dan pengukuran. Pada penelitian ini, kajian mengenai kekasaran permukaan suatu logam dilakukan dengan menggunakan pengukuran langsung dan menggunakan analisis citra gambar. Adapun teknik pengukuran langsung dilakukan dengan menggunakan Surftest pada 20 titik (5 titik dari diagonal sisi kanan, 5 titik diagonal sisi kiri, 5 titik vertikal dan 5 titik horizontal) sedangkan analisis citra gambar dilakukan dengan menggunakan Image-J pada foto gambar permukaan besi. Berdasarkan metode penelitian yang telah dilakukan diperoleh kesimpulan yaitu semakin besar nilai grit abrasive paper yang digunakan pada permukaan besi, maka nilai kekasaran permukaan besi semakin kecil/semakin halus (nilai kekasaran permukaan cenderung menurun). Sedangkan hasil pengolahan citra gambar yang dilakukan dengan Image-J telah berhasil menunjukan surface plot permukaan sampel besi. Selain dari itu, gray value dari citra gambar yang dihasilkan mengalami fluktuasi seiring dengan semakin panjang/besarnya distance (pixels).

The effect of surface roughness on oblique bicycle helmet impact tests

The friction between a helmet and impact surface affects the accelerations imparted to the head. The roughness of the impact surface is, therefore, a consideration when developing oblique impact standards. An 80-grit abrasive paper is commonly used in oblique impact tests to simulate a road surface, but has not been validated for bicycle impacts and may not accurately represent real road surfaces. In the following study, a helmeted NOCSAE headform with a Hybrid III neck was dropped onto a 45° anvil at 6.5 m/s using a twin wire guided drop tower. Helmeted drops were performed in two orientations (frontal and side) on road surfaces, roughened steel surfaces, 80-grit abrasive paper and a low friction surface. For each impact, measures of linear and rotational acceleration were obtained. These metrics were compared across impact orientations and surfaces to assess the influence of surface roughness on headform impact response. Frontal impacts were less sensitive to the impact surface roughness than side impacts across metrics. Among metrics, rotational acceleration showed the largest effect due to surface roughness. Compared to the road surface, peak rotational acceleration from impacts on the 80-grit surface were 6.5% less and 48% greater for frontal and side impacts, respectively. Based on consideration of the peak and cumulative impact measures, steel impact surfaces appear to better simulate road impact than the commonly used 80-grit abrasive paper.

Abrasive Wear Mechanism of Microwave-Assisted Compression Molded Kenaf/HDPE Composite

The present work aims to study the abrasive wear of kenaf/high-density polyethylene (HDPE) composites with 20% weight fraction reinforcement of the kenaf fiber. A unique technique of the microwave-assisted compression molding (MACM) was used to fabricate the composites. The pin-on-disc setup was used for two-body abrasive wear, in which the kenaf/HDPE composite acts as a pin and the abrasive paper (P100) acts as a counter surface. Two-body abrasive wear tests were conducted for HDPE and kenaf/HDPE composites at normal loads of 10 N, 20 N, and 30 N and the sliding speed of 1 m/s, 2 m/s, and 3 m/s within 100 m of sliding distance. Tribofilm formation was observed at higher values of load and speed, which helps in reducing the wear-rate of the composites. Wear mechanism of the kenaf/HDPE composite is discussed in detail and supported with scanning electron microscope (SEM) fractography.

INFLUENCE OF SURFACE POLISHING ON THE FRICTION BEHAVIORS OF NBR

An experimental study on the tribology behavior and mechanism of NBR-Steel pair has been carried out. Abrasive paper was used to polish the NBR surface. The influences of surface topography on the friction coefficient were investigated based on the block-on-ring tribometer. Results show that polishing with abrasive paper is an effective method to reduce the friction coefficient of NBR on steel. Superlubricity was also found in the test. A new method to explain the superlubricity based on the contact angle and surface molecular structure was put forward in this work. Abrasive paper polishing changes the surface asperities, so affects the contact angle, so as to influence the boundary limiting shearing strength, and then causes the superlubricity. During the friction process the microstructure obviously changed, along with mechanical breaking of the molecular chain.