Sheet Metal and Non-Metallic Structures (1) When performing a ring (coin tap) test on composite structures, a change in sound may be due to damage or to transition to a different internal structure. (2) The extent of separation damage in composite structures is most accurately measured by a ring (coin tap) test. Regarding the above statements, a. both No. 1 and No. 2 are true. b. only No. 1 is true. c. only No. 2 is true.