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<p>[QUOTE=&quot;mithril21, post: 3460157, member: 102153&quot;]1: There is another secondary crack on the obverse which hasn&#039;t yet fully propagated to the reverse.&nbsp; </p><p>2: Surface texture and changes in surface roughness. Generally speaking, the roughness increases as a crack propagates, so the fracture progresses from smooth to rough. In some cases, the initiation side can be determined by the straightness of the fracture edge. It appears the fracture is smoothest at the center on the observe side and then becomes rougher as it propagates towards the reverse and edges of the coin. Correct me if I&#039;m wrong on this.&nbsp; </p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>Yes, the impact on the reverse side creates tension stresses on the obverse side. If you bend something until it breaks, what side does it break from? And no, it was not hit by a bullet. </p><p><br /></p><p><br /></p><p>[ATTACH=full]920226[/ATTACH] </p><p><br /></p><p><br /></p><p><br /></p><p>There are four types of fracture mechanism in metals:</p><p>1. Ductile</p><p>2. Brittle transgranular </p><p>3. Brittle intergranular </p><p>4. Fatigue </p><p><br /></p><p>Beach marks and ratchet marks are both fatigue features. It it best to view fractures using &quot;glancing light&quot;. Try turning off the overhead light, take a flashlight and shine it across the fracture surface from the side. This will creates shadows that will better highlight the surface topography. </p><p><br /></p><p><br /></p><p><br /></p><p>It just rules out inherent brittleness (e.g. faulty heat treating). Macroscopic brittle fracture can occur in a ductile material for other reasons such as rapid loading (high strain rate). Take some taffy or slime and try pulling it apart very rapidly versus very slowly. Pulling it slowly will cause it to stretch and deform a lot more before breaking. Pull it apart fast and it will immediately break with little deformation. Same is true for ductile metals. </p><p><br /></p><p><br /></p><p><br /></p><p>Lets see a higher magnification shot from the fracture origin. Near the center on both obverse and reverse edges, in case I was wrong about which side it initiated from.[/QUOTE]</p><p><br /></p>

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