Comments on: Con Rods: Application of Shot-peening http://www.ret-monitor.com/articles/777/con-rods-application-of-shot-peening/ Specific mission-critical info for professionals Mon, 21 May 2012 22:29:59 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: Terry http://www.ret-monitor.com/articles/777/con-rods-application-of-shot-peening/comment-page-1/#comment-6157 Terry Thu, 20 Jan 2011 05:24:40 +0000 http://www.ret-monitor.com/articles/777/con-rods-application-of-shot-peening/#comment-6157 To understand why shot peening can improve fatigue life for engine parts like conrods or valve springs, you need to understand the basic process of fracture mechanics. For metal parts subjected to cyclical bending or torsional loads, the point of highest tensile stress will normally occur somewhere on the extreme outer surface of the part. With these parts, cracks will only form due to excessive tensile stresses. Putting the surface into compressive preload by shot peening will reduce the peak tensile stress that surface experiences for a given load, since the surface won't go into tension until the compressive preload is overcome. Besides shot peening, conrod fatigue life can be improved by removing surface stress concentrations, such as the grinding scratches mentioned in the article. Mechanically working the surface by cold rolling is also effective, and this is done with conrod bolt head fillets and crank pin fillets. Another important factor is material grain, which is why forged rods are preferred. And finally, material cleanliness is critical, since any inclusions present in the metal will create fracture nucleation points. To understand why shot peening can improve fatigue life for engine parts like conrods or valve springs, you need to understand the basic process of fracture mechanics. For metal parts subjected to cyclical bending or torsional loads, the point of highest tensile stress will normally occur somewhere on the extreme outer surface of the part. With these parts, cracks will only form due to excessive tensile stresses. Putting the surface into compressive preload by shot peening will reduce the peak tensile stress that surface experiences for a given load, since the surface won’t go into tension until the compressive preload is overcome.

Besides shot peening, conrod fatigue life can be improved by removing surface stress concentrations, such as the grinding scratches mentioned in the article. Mechanically working the surface by cold rolling is also effective, and this is done with conrod bolt head fillets and crank pin fillets. Another important factor is material grain, which is why forged rods are preferred. And finally, material cleanliness is critical, since any inclusions present in the metal will create fracture nucleation points.

]]>