The use of the direct impact Hopkinson pressure bar technique to describe thermally activated and viscous regimes of metallic materials
The influence of strain rate over domains involving the thermal activation and the viscous drag behaviour of the dislocations is discussed. While it is recognized that the Koslky–Hopkinson technique or split Hopkinson pressure bar technique can generate data up to the upper strain-rate limit of the thermal-activated regime, it is necessary to use a direct impact Hopkinson pressure bar technique to access the viscous regime. Data generated with this technique are presented for a series of metals, including steel, nickel, copper and tungsten alloys. The motivation to generate such data is provided through three industrial applications.
The influence of the dynamic loading rate on tensile failure properties of metallic materials
The influence of the dynamic loading rate on the tensile failure properties of a series of tungsten alloys and an austenitic stainless steel were investigated by evaluating the flexural strength with unnotched and notched Charpy specimens. These data were generated with a newly developed Hopkinson pressure bar technique. The technique consists in impacting with a striker, at velocities ranging from 25 to 160m/s, a round bar specimen placed against two incident Hopkinson pressure bars. Through the recording of the striker velocity before and after impact, failure energy is deduced. At impact velocities greater than 30m/s, the results reveal a surprising increase of the Charpy energy with the increase of the impact velocity for both types of metallic materials. The results have been interpreted through numerical simulations of the Charpy test, the dependence of the material flow stress with the strain rate, and observations of the failure mechanisms. It was found that at impact velocities greater than 30m/s, tangential strain rates exceed 3000s −1 at the failure initiation site of the Charpy specimen. These strain rates are within the strain rate regime where strengthening occurred due to the viscous behaviour of the dislocations. Data generated with moderate stress concentration using notched round bar Charpy specimens indicate that the strengthening occurring at high strain rates continues to pilot the tensile failure processes.
Morphological characterization of Eustrongylides sp. larvae (Nematoda, Dioctophymatoidea) parasite of Rhinella marina (Amphibia: Bufonidae) from Eastern Amazonia.
Absctract Eustrongylides spp. nematodes have birds as final hosts and uses other vertebrates as intermediate/paratenic host (fish, amphibians and reptiles) and have zoonotic potential. In amphibians, the larvae may be located in the subcutaneous tissues, liver and mesentery, between the muscle fibres, especially in the lower limbs. Rhinella marina, which is widely observed in Brazil, has exhibited complex diversity in its helminth fauna, reflecting the unique habitat of the Amazon biome. For the first time, this study describes the morphological aspects of third-stage larvae of Eustrongylides sp. in Rhinella marina from Santa Cruz do Ararí, Marajó Archipelago, Eastern Amazonia, using light and scanning electron microscopy.