Originally Posted by
carlos danger
carbon is no different to other frame materials when searching for suspected cracks imo.
Metals are homogeneous and isotropic, exhibiting the same strengths and stiffness in all directions. Composites (carbon fiber, fiberglass, et all) are
anisotropic, providing different strength and stiffness depending on the orientation of the fibers in the resin matrix, which is one of their advantages; A carbon frame can have the down tube wrapped at 45 degrees off the long axis in both directions to provide excellent torsional stiffness (to prevent twisting under hard climbing), yet some longitudinal bending flex for better ride quality. For damage to a composite, the amount of discontinuities in the fibers determines structural integrity. Metals are generally more tolerant, though not all; some metals are particularly "notch sensitive", and even surface scratches can propagate under high stresses or high cycle fatigue loads. For composites, a damaged section that is "soft" (damaged resin matrix) may still transmit loads fine under local tension, but buckle under local compression; the engineering term for this is "you can't push on a rope".