Determination of Impact Behavior of ABS From Acoustic Emission, Ultrasound and Optics
Authors: Dundar Mehmet Akif , Ayorinde Emmanuel , Al-Zubi Mohammad 
Published: March 2016

ABS (Acrylonitrile Butadiene Styrene) is an industrially-important and widely used amorphous thermoplastic on which billions of dollars are spent annually in USA. Its applications cover impact-mitigation, infrastructural and laboratory piping systems, sports goods, musical instruments, automotive trim components and bumper bars, medical devices, enclosures, protective headgear, marine craft, luggage, domestic appliances, toys, consumer goods, edgings for industrial goods, etc. Its use to contain impact damage is primary; hence continued research in this area is warranted.

The novelty and contribution of this work lies in its employment of more deeply insightful parameters and methods of characterization in acoustic emission and ultrasonics, as well as advanced optical microstructural characterization with sophisticated instrumentation, on one hand, and the wider correlations and conclusions now made possible by these means.

In the work which this paper reports, the impact response behavior of ABS material under various levels of impact energy was investigated using results obtained from the mechanical test, and parameters obtained from non-destructive test methods such as Acoustic Emission (AE), Ultrasonics, and Optical Inspection.

The ABS plates were impacted by a hemispherical steel projectile in a drop-weight impact tester. Two AE sensors were placed on the surfaces of ABS plates during the impact tests. After the impact tests were completed, ultrasonic C-Scan investigation of the damaged areas was also carried out, and sections were inspected under the microscope. Correlations between damage areas and various parameters of the non-destructive diagnostic test methods utilized were explored. ABS is one of the most highly impact-resistant materials utilized in industry. Its characterization under impact is therefore very important, in order to devise ways of enhancing properties that would make the material or structures made from it, better in service.

In this work, plate samples of rectangular shape were subjected to central impacts from a spherical impactor released from various heights. It is of interest to know how the impact propagates through the plate thickness, and how the microstructure is affected from point to point, both laterally and depth-wise. The issues of energy transfer and dissipation are significant in terms of the effectiveness of the material as an impact deadener.

Three non-destructive methods are utilized in this work for comprehensiveness and effectiveness. The AE approach is broadly divisible into two — classical, and transient. The former has dozens of descriptive parameters per each of the three dimensions, while the latter, which is based on the waveform and its several possible transforms, adds even many more possibilities. Thus, characterization in AE is particularly rich, and, when a sufficient number of appropriate parameters are utilized, has a very high probability of correctly depicting what is really going on in the material or structure under inspection. The ultrasonic scan reveals in color-code the variation of the material homogeneity throughout the scanned space, which, in each case, covered the whole plate. This normally provides a good picture of damage and its intensity variation in the test piece. The microstructure of selected parts of the test pieces before and after impact was inspected with a violet laser microscope. In this instrument, reflecting light from the white light source is detected with a color CCD camera. This camera obtains color information at the peak (focal point) detected with the laser light source on a pixel basis, thus enabling a real color examination, which SEMs cannot do. This instrument also uses a pin hole confocal optical system which enables high accuracy measurement and high definition examination by eliminating reflecting light from points other than the peak.

The results obtained showed clear relationships between energy and geometrical and material metrics of damage through the damage zone and shed more light on possible pathways to the desired enhancement of impact resistance in this case.