Dear sir,

I'm from india doing postgraduation in mechanical engineering .In my project work we performed shotpeening on wrought Al 1100 (ultimate strength = 156 Mpa)by glass bead and pressure 1 kgf/cm2 with nozzle tip distance of 4 in and exposure time of 40 sec .My specimen surface finish was deteriorated by shotpeening and fatigue testing on these specimen shows reduced fatigue life.How this can be possible? Please help me to understand this and give your valuable suggestion for it .
THANKING YOU.

Peening with glass beads can be detrimental to the surface, causing damage and early fatigue failure. Generally the intensity range when using glass bead is limited to only the "N" scale.
What was the intensity of your peening treatment?

Glass beads will break very easily at higher than 5A intensity so you never should peen while at the "A" range of intensity.
Are you familiar with intensity measurements and the Almen strip, holder and gage?