NASA’s Langley Research Center has developed a portable device to simulate low-velocity impacts on a material or structure. As composite materials are highly susceptible to damage caused by low-velocity impact, they must be designed and evaluated for structural integrity after these types of impacts. The NASA impactor’s design comprises an exterior tube, an instrumented projectile, a spring to propel the projectile, a spring compression device, a release pin, a wooden spacer/locator block, and an optical sensor. The tube can be handheld or rigidly mounted at any angle such that the impact response can be evaluated at specific positions on the test article. In the current configuration, impact energies between 4 and 40 J (between about 3 and 30 ft.-lbs.) can be obtained. Researchers designed a fully functioning prototype for the NASA Engineering and Safety Centers (NESCs) Composite Crew Module (CCM) program for damage tolerance testing. Both the impact force history and projectile velocity are captured during operation.
The projectile itself contains a commercial load cell designed to obtain the dynamic force response during the impact event. Furthermore, a digital oscilloscope and optical sensor are combined to measure the velocity just prior to impact so that the impact energy of the projectile onto the test surface can be calculated. Impact energies can be adjusted by changing the spring to one with a different spring constant.
The impactor device weighs about 15 pounds. It is primarily designed for use on composite structures because they are highly susceptible to damage from low-velocity impacts where the damage may not be visible but results in great loss of strength. If the damage cannot be detected visually, it can be seen through nondestructive testing (ultrasonic, flash thermography, or X-ray). However, the device may also be used on structures to evaluate and tune structural health monitoring systems.
The technology has been designed, prototyped, and implemented in four military or government programs for impact testing on metallic and composite structures, including a helicopter roof in 2013. The cost of the parts for the prototype was approximately $9,000. Production costs are expected to be lower.
The impact tester device can be used in aerospace for investigating impact damage resistance or tolerance of small coupons or large structures, in aviation for testing structural health of existing vehicles, and in automotive for assessing durability and damage tolerance of metallic or composite parts.