PSI - Issue 14

R.K. Kumar et al. / Procedia Structural Integrity 14 (2019) 134–141 S. Anand Kumar / Structural Integrity Procedia 00 (2018) 000–000

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orthogonal design. Two factors such as, exposure time (T) and peening pressure (P) are used in this study and the full factorial design matrix is shown in Table 3. 3. Results And Discussion 3.1. Coverage Area (C)

Fig. 1 (a) Variation of ‘C’; (b) Contour of % ‘C’as a function peening pressure, exposure time

Fig. 2 Mean effects of factors on ‘C’

One of the foremost control parameter, which decides the efficiency and reproducibility of any SP process, is the degree of coverage. ‘C’ is defined as the ratio of the area covered by the shot impact to the entire surface of the peened sample, expressed as a percentage. It is generally recognized that, the full coverage should be 100 % in most of the practical industrial applications in order to enhance the fatigue behaviour reported by Vielma, (2014). Fig. 1a shows the influence of SP process parameters on ‘C’ by the experimental design. Fig. 1b shows the effect of shot peening parameters on the evolution of ‘C’. It is clear that, increasing the both exposure time and peening pressure increases the ‘C’. In general, exposure time is the co-action of two factors such as the number of times that the shot stream strikes over a specific location on the part and the velocity of the shot stream during peening reported by Wagner, (2009). Fig. 2 shows the mean of the two factors at each level indicating the influence of exposure time on ‘C’ is more predominant than that of the peening pressure. It is observed that the percentage of coverage values increases steeply as the exposure time is varied from 5 to 20 min. Also the % of coverage reaches optimum levels (100 %) after exposure time of 20min, indicating the full coverage of surface. The mathematical relationship between the percentage of coverage, exposure time, peening pressure were established by regression equation C (%) = - 4.625 + 3.99 T + 9.8 P; (R 2 = 93%) (1) Further, analysis of variance (ANOVA) method was used to calculate the fisher’s ratio (F) that affects the percentage of coverage. The F value for each factor was calculated for percentage of coverage and shown in table 4. The observed F value for this study is 3.07 i.e. 90 % confidence level reported by Roy (1990).

Table 4. ANOVA for ‘C’

Factors

Sum of squares

Degree of freedom

Variance 2683.50

F value

Exposure time (min) Peening Pressure (bar)

8050.5 1068.5 498.0 9617.0

3 3 9

48.50 6.44

356.17 55.33

Error Total

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15

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3.2. Almen Intensity (AI) Fig. 3a shows the influence of shot peening process parameters on ‘AI’ by the experimental design. The components peened with lower or higher ‘AI’ observed to exhibit inferior fatigue lives. Fig.3b shows the effect of shot peening process parameters on the evolution of ‘AI’. The increase in the ‘AI’ has a significant effect compared to influence of ‘C’. For the constant shot mass, enhancement in ‘AI’ implies, greater impact velocity, owing to the increment in the