PSI - Issue 42

Mushfiq Hasan et al. / Procedia Structural Integrity 42 (2022) 1169–1176 Mushfiq Hasan et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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used to capture profiles which were post-processed using a commercial software named Mountainmaps. A binary imaging technique stated in (12) was followed to quantify wear and pitting. A visual representation of the imaging process is illustrated in Fig.2. Each sample was examined and the average of four readings at different locations was taken to evaluate the final value.

Fig. 2: Surface map over a pitted wear track and associated binary images

3. Result and Discussion The effect of the slide to roll ratios, surface roughness and surface treatment on micropitting are described in the following sections. Moreover, the simultaneous micropitting and wear propagation mechanism is also explained and visualised in the later part. The overall objective is to study if there is any variation in micropitting growth that is influenced by the above parameter under severe contact conditions. 3.1. Effect of Slide to Roll Ratios (SRR) During the slide to roll ratio study, negative sliding was imposed to accelerate the micropitting (13,14). Therefore, one of the disks was slower than another one. Hardness and roughness were the same on both the disk surface to study the sole effect of SRR on the damage mechanism. By some separate experiments, the maximum SRR that can be imposed safely was estimated for this friction pair. It was found that the contact became seized if the sliding speed was more than - 2 m/s at 80⁰C operating temperature. Therefore, to avoid this problem maximum sliding speed in our study was -1.39 m/s to achieve an SRR of -0.45. In this investigation, three relatively higher sliding conditions (-0.79, -1.09 and -1.39 m/s) have been studied, which can be found in transmission applications while the torque requirement is maximum. Higher sliding enhances the number of stress micro cycles during each passage of contact. The experimental data shows variation in micropitting and wear volume by imposing different SRRs, as presented in Fig.3(a). Among three cases, the maximum amount of micropitting has been traced for the lowest sliding speed that was tested. With increasing SRR, there is a growth in wear volume and an opposite effect for micropitting.

0.12

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12

1.5 Mil 4.5 Mil

MP Wear

3.297

3.5

0.104

0.10

0.093

3.0

0.081

0.021 Wear Volume (mm 3 )

Wear Volume (mm 3 ) 0.04 0.06 0.08

2.303

2.5

0.062

1.835

2.0

0.045

1.5

1.0

Micropitted Area (%)

0.02

0.5

0.00

0.0

Test 2 (-0.79)

Test 3 (-1.09)

Test 4 (-1.39)

Test 2 (-0.79)

Test 3 (-1.09)

Test 4 (-1.39)

Test at different sliding speed (m/s)

Test at different sliding speed (m/s)

Fig.3: (a) Effect of SRRs on wear and micropitting (b) Wear volume comparison at 1.5 million and 4.5 million cycles (a) (b)