Experimental study by pyrometry of Portevin–Le Châtelier plastic instabilities—Type A to type B transition

Abstract

The dynamic strain aging phenomenon which occurs in some materials under certain temperature and strain rate conditions can cause a localization of the plastic strain in the form of Portevin-Le Châtelier (PLC) bands. According to the strain rate and the temperature, the spatiotemporal pattern of these bands changes and three main types of band are identifiable (types A-C). The increment of plastic strain associated with each band causes an increment in temperature which can be measured by infrared pyrometry. This experimental technique was used in this paper to study the PLC phenomenon in an aluminium-copper alloy at ambient temperature and to visualize the strain localization patterns. Some characteristics of these bands are measured: bandwidth, slope angle, increment of plastic strain in the band, time between two band formations, time of band formation, propagation velocity of the bands, band spacing... The evolution of these characteristics according to the strain enables us to suggest an explanation of the type A-type B transition.

An experimental investigation of the behaviour of steels over large temperature and strain rate ranges

“…This phenomenon may be identical to instabilities encountered in the literature [21,22]. For the phenomenon of ageing dynamics, this inversion of the sensitivity of the stress as a function of temperature can be observed.…”

The Portevin–Le Chatelier effect: a review of experimental findings

“…Similarly, aluminum alloys at certain strain rates and temperatures exhibit only one type of band, until the temperature or strain rate is changed [33,[37][38][39]. A series of studies conducted by Jiang et al [37,38] and Ranc and Wagner [40] have shown clear transitions among the serration types in Al-Cu alloys; the transitions have been observed using digital speckle correlation, pyrometric and digital image correlation (DIC) techniques on the surfaces of flat specimens during tensile tests.…”

“…To visualize the formation of PLC bands and accurately determine the band velocities, the thermal camera may be coupled with a pyrometer in an infrared pyrometry system such as that used by Ranc and Wagner [92]. Generally, the specimen surface is coated with a thin layer of black dye to homogenize the surface emissivity [40]. As thermographic methods have much higher data acquisition frequencies than DIC, DSPC and LST they are better at resolving the temporal features of PLC bands.…”

Forming performance of an as-quenched novel aluminum-lithium alloy

“…PLC effect, which is characteristic of inhomogeneous deformation band and repeated stress serrations, has an adverse influence on the ductility, corrosion resistance, and the surface quality [12]. It has been reported that the Al-Mg and Al-Cu alloys after quenching are inclined to suffer the PLC effect [13][14][15]. However, related investigations are rarely conducted on aluminum-lithium alloys.…”