Interface damage characterization of carbon-epoxy composite materials

This research shows a novel in-situ experimental approach to characterize a carbon-epoxy unidirectional composite system interface. Computational models were implemented to support the experimental campaign and identify the interface properties. After validating the computational model with experimental results, it was employed to study the behaviour of interface debonding under both mode I and mode II damage. By utilizing the validated model, it becomes possible to assess the consistency of the proposed experimental approach in characterizing the interface, with the aim of generating in future an analytical model able to predict interface characteristics.&nbsp

Vliv kladných pulzů na HiPIMS depozici tvrdých DLC vrstev

Diamantu podobné uhlíkové vrstvy (DLC) byly připraveny novou metodou HiPIMS zahrnující kladné pulzy na terči po skončení hlavního (záporného) pulzu. Byl zkoumán vliv amplitudy kladných pulzů na výbojové podmínky a mechanické vlastnosti připravených vrstev. Při použití kladných pulzů byla zjištěna zvýšená ionizace argonu i uhlíku. Hmotnostní spektroskopie potvrdila vytváření většího množství vysokoenergetických iontů C+, přičemž střední energie iontů roste s amplitudou kladného pulzu. Bombardování rostoucí vrstvy těmito ionty vede k vyšším hodnotám hustoty DLC vrstev a k vyššímu tlakovému pnutí ve vrstvách.Diamond-like Carbon (DLC) coatings were deposited by a novel HiPIMS method that incorporates positive voltage pulses at the end of the conventional HiPIMS discharge. Different positive voltage amplitudes were used to evaluate the effect of this operation mode on the discharge process and the mechanical properties of the deposited DLC coatings. The application of positive pulses was observed to enhance the ionization of both the sputtered carbon and argon species. Mass spectroscopy measurements showed that a larger amount of high-energy C+ ions are generated, with ion energies proportional to the amplitude of the overshoot voltage. The ion bombardment induced by the positive pulses led to higher compressive residual stresses and densification of deposited DLC coatings

Tribomechanical properties of hard Cr-doped DLC coatings deposited by low-frequency HiPIMS

Cr-doped diamond-like carbon (Cr-DLC) films with Cr contents ranging from 3 up to 20 at. % were synthesised in a codeposition process with HiPIMS (Cr deposition) and DC-pulsed technology (C deposition). The application of HiPIMS at low frequencies was observed to significantly enhance the energy density during the Cr plasma discharge due to the interaction of Cr–C species. The higher energy bombardment at low HiPIMS frequencies allowed doping with Cr the DLC structure avoiding the graphitization of the carbon structure. EELS spectroscopy was used to evaluate sp3 content and Raman was used for sp2 structural characterization of the films. Enhanced mechanical properties (hardness up to 30 GPa) were observed with nanoindentation for Cr-doped DLC at low frequencies. High temperature nanoindentation tests were also performed from room temperature to 425 °C in order to evaluate the evolution of hardness and Young Modulus with temperature. The results showed that the mechanical properties at high temperature mainly depend on the initial sp3-sp2 structure. Tribological tests were carried out in air from room temperature to 250 °C. Cr-doped DLC coatings deposited by low-frequency HiPIMS showed lower friction and wear compared to undoped DLC.Peer reviewe