LOW VELOCITY IMPACT DAMAGE IDENTIFICATION OF COMPOSITE LAMINATE USING DYNAMIC STRAIN SIGNALS

Fourteen levels of impact energy were designed in order to identify the damages of composite laminates. Corresponding to the minimum level of impact energy, composite laminates were intact. Corresponding to the maximum level of impact energy, composite laminates were penetrated through. Strain responses during the impacts were used to detect impulse damages of composite laminate specimens. Based on the collected impulse strain signals under the impacts, the following ten new impact damage indexes are suggested. They are rising shock duration (RSD, the interval from the starting time to peak time of the impact), descending shock duration (DSD, the interval from the peak time to the end time of the impact), shock duration (SD, the interval from the starting time to the end time of the impact), the ratio of the RSD to the DSD, the ratio of the DSD to the RSD, rising area (RA, the integral of the impulse strain response from the starting time to the peak time of the shock), descending area (DA, the integral of the impulse strain response from the peak time to the end time of the shock), total area (TA, the integral of the impulse strain response from the starting time to the end time of the shock), the ratio of the RA to the DA, the ratio of the DA to the RA. The relationship between the ten damage indexes and the impact energies was researched. The results indicate that such indexes as the DSD, the SD, the DA and the TA vary monotonically, depending on the increasing impact energies on the whole. Thusly, the four damage indexes are suitable for identifying the impact energies within the range from 0.8J/mm to 6.67J/mm. The six rest damage indexes can identify impact damage quantification within some shock energy range. The results also show that the DA and TA can also be used to identify the impact location.