Quantitative Impact Testing of Energy Dissipation at Surfaces

Abstract

Impact testing with nanoscale spatial, force, and temporal resolution has been developed to address quantitatively the response of surfaces to impingement of local contact at elevated velocities. Here, an impact is generated by imparting energy to a pendulum carrying an indenter, which then swings towards a specimen surface. The pendulum displacement as a function of time x(t) is recorded, from which one can extract the maximum material penetration x max , residual deformation x r , and indentation durations t in and t out . In an inverse application one can use the x(t) response to extract material constants characterizing the impact deformation and extent of energy absorption, including material specific resistance coefficient C in , coefficient of restitution e, and dynamic hardness H imp . This approach also enables direct access to the ratio H/E, or resilience of the deformed material volume, at impact velocities of interest. The impact response of aluminum was studied for different contact velocities, and the mechanical response was found to correlate well with our one-dimensional contact model. Further experiments on annealed and work hardened gold showed that dynamic hardness H imp scales with contact velocity and highlighted the importance of rate-dependent energy absorption mechanisms that can be captured by the proposed experimental approach.

Nano-impact testing of TiFeN and TiFeMoN films for dynamic toughness evaluation

“…The nano-impact (impulse indentation) technique in the NanoTest system can simulate the mechanical conditions occurring in contact and predict the wear performance of coated systems subjected to repetitive contact [2,[29][30][31][32]. In this test repetitive high strain rate impact indentation occurs at the same location on the sample surface and the evolution of film damage can be monitored in situ.…”

Influence of test methodology and probe geometry on nanoscale fatigue failure of diamond-like carbon film

“…Constantinides et. al has indicated that the for various loading conditions v in for the NanoTest TM system can range from 0.7 mm/s to 2.5 mm/s [38]. As the load was low in the current investigation, a lower value of 0.7 mm/s can be assumed as average to cover the loading range considered in this investigation.…”

“…These instruments for example may be used to evaluate the damage analysis on solar panels during a sand storm with a typical sand particle velocity of 50 km/hr ≈ 1.4 × 10 4 mm/s. Although such velocity is not achievable by the indenting probes in either of the systems discussed above, there is difference in the mass of indenter (effective mass of pendulum and tip is 0.21 kg for the NanoTest TM system [37][38]) and the mass of typical sand particle (≈10 -5 kg to 10 -6 kg). This difference in mass can be used to compensate the lower impact velocity of nanoindentation system, and hence can impart the correct momentum and energy during the dynamic contact.…”

Advanced Nanomechanical Test Techniques

“…Single impact experiments are typically used to determine the "dynamic hardness" of a sample [100][101]. This is the effective hardness of the material at a given rate of strain.…”

“…The dynamic hardness in this test was 8 GPa compared with around 5 GPa under quasi-static conditions. Constantinides and coworkers reported [101] that gold was even more sensitive to strain rate but aluminium was much less so ( …”