Eyeglass Hinge The principal loading of this hinge was bending about the axis of the screw hole, so the fatigue crack started at the side closest to the hole where the tensile stress was highest.  The thin-ness of the multiple-leaf hinge caused additional bending stresses about the orthogonal axis, so the striations on the fracture surface have the shape of chevrons pointing towards the fracture origin. Click on the image titles to see the corresponding animated models created by Helicon Focus and Helicon 3D Viewer. Right-click on each image and select View Image to see it at full resolution in a new browser window.

Overall View - 25X Stack: 0.003 inch increments.	Fracture Surface at 45X Stack: 0.001 inch increments.