Abstract
An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrical compression) test method for brittle materials is utilized along with conventional split-Hopkinson pressure bars (SHPB) for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. To eliminate the complexities of conventional strain gage application, a non-contact Laser Occluding Expansion Gage (LOEG) has been adapted for measuring the diametrical transverse expansion of the specimen under high-strain rate diametrical compressive loading. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of xGnP (exfoliated graphite nanoplatelets) reinforced and additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses shows the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. The contribution of reinforcement to the tensile properties of the candidate materials is presented.
Highlights
Robust material models obtained from the physics of high-stain rate material response are essential for the large scale finite element simulations of automotive crashworthiness; aerospace impact including foreign-object damage, such as, bird ingestion in jet engines and meteorite impact on satellites; dynamic structural loading, such as, the events occur during earthquakes; high-rate manufacturing processes, including high-rate forging, machining, wire drawing and cold rolling; and research for military technologies focusing on ballistics, detonation physics, projectile and armor interactions [1]
Experimental facilities used in this study consist of a traditional compression split-Hopkinson pressure bar system that has been modified to conduct indirect dynamic tensile tests on nanocomposite specimens based on conventional Brazilian disk test method
The energy absorption capacity of pure vinyl ester is adversely affected under high-strain rate loading, whereas it is improved with the addition of xGnP reinforcement (Figure 10(iii-a) and Figure 11(iii-a))
Summary
Robust material models obtained from the physics of high-stain rate material response are essential for the large scale finite element simulations of automotive crashworthiness; aerospace impact including foreign-object damage, such as, bird ingestion in jet engines and meteorite impact on satellites; dynamic structural loading, such as, the events occur during earthquakes; high-rate manufacturing processes, including high-rate forging, machining, wire drawing and cold rolling; and research for military technologies focusing on ballistics, detonation physics, projectile and armor interactions [1]. The specimen strain measurement at high rates is traditionally based on the response from strain gages mounted on the bars of a SHPB system. An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. The complexities of conventional strain gage application on the specimen for measuring the diametrical transverse expansion of the specimen under high-strain rate diametrical compressive loading are eliminated by adapting a non-contact LOEG technique [42] [43]. High-speed digital photography is performed for diagnosing the specimen failure mechanism and validating the indirect test method for characterizing the tensile properties of graphite platelet reinforced and CTBN toughened vinyl ester nanocomposites. The effect of strain rate and the contribution of xGnP reinforcement and CTBN toughening on the tensile properties of vinyl ester based nanocomposites are presented
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