ABSTRACT
This study investigates the influence of strain rate on plastic deformation developed in the flange of a steel road barrier. This effect can be investigated by the use of the uniaxial tensile test. It was found that the strain rate increases yield as well as ultimate strength and gently drops down the elongation at break. Moreover, the accelerated strain rate is connected with matrix heating and increasing the Taylor-Quinney coefficient. Despite the valuable matrix heating and the higher Taylor-Quinney coefficient at the higher strain rates, samples necking is initiated earlier and dislocation density is higher. Flange grains become preferentially aligned along the direction of uniaxial stress, especially at the higher plastic strains. Finally, surface Zn protective layer delamination is initiated quite early beyond the yielding. It is considered that the cracks are due to the different response of the Zn allayer and underlying steel matrix on the plastic straining. Increasing strain rate attenuates the degree of Zn layer delamination.
ABSTRACT
Low alloyed steels of low, medium, or high strength are frequently used for many applications in the automotive, civil (bridges), aerospace, and petrochemical industries. A variety of thermomechanical regimes, in which these steels can be produced, enable customization of their matrix with respect to their fatigue resistance, resistance against friction and impact wear, fracture toughness, corrosion resistance, etc. This study analyses the influence of magnetising conditions on Barkhausen noise and other extracted parameters. It was found that the increasing magnetising frequency makes Barkhausen noise weaker, especially in the high strength low alloyed steels, as a result of the decreasing magnetic field in a sample. For this reason, increasing fraction of domain walls is unpinned at the higher frequencies. Barkhausen noise for the high strength low alloyed steels at higher frequencies is remarkably attenuated. Moreover, the different behaviour with respect to direction of the sheet rolling and the transversal direction, can be found due to realignment of the domain walls. This study demonstrates that the position of Barkhausen noise envelopes and the number of Barkhausen noise pulses increase in a systematic manner at the lower magnetising frequencies. Those parameters can be employed for distinction of the low alloyed steels, investigated in this study. However, the increasing magnetising frequency makes attenuation of Barkhausen noise more remarkable for the low alloyed steels of the higher strength. Therefore, the effective value of Barkhausen noise, at the magnetising frequency 750 Hz, in the rolling direction exhibits the systematic descent along with the increasing yield strength. This parameter can be used for distinction of the low alloyed steels after their thermomechanical processing, as well.
ABSTRACT
This study deals with monitoring of Zn layer heterogeneity on the flange of steel road barriers using magnetic measurements. The Barkhausen noise technique is employed for such purpose, and parameters extracted from Barkhausen noise signals are correlated with the true thickness of the Zn layer. The true values of the Zn layer were obtained from the metallographic images, as well as the thickness gauge CM-8825FN (Guangzhou Landtek Instruments Co. Ltd., Guangzhou, China) device. It was observed that the diffusion region lies below the Zn protective layer, which makes the thickness of the Zn layer obtained from the CM-8825FN device thicker than that measured on the metallographic images. For this reason, the chemical gradient of Zn below the Zn layer can be reported, and it affects Barkhausen noise emission. Barkhausen noise decreases along with increasing thickness of the Zn layer, and Barkhausen noise envelopes are shifted to stronger magnetic fields. The number of strong MBN pulses drops down with the increasing thickness of Zn coating at the expense of the increasing number of the weak MBN pulses. The thickness of Zn coating can be polluted by the solidification of Zn melt after galvanizing. The presence of the diffusion layer dims the contrast between ferromagnetic and paramagnetic phases.
ABSTRACT
This paper investigates the rate of transformation induced plasticity in TRIP steel (TRansformation-Induced Plasticity) after plastic straining by the use of Barkhausen noise emission. The samples were subjected to a variable degree of plastic straining and analysed by the use of conventional techniques such SEM, XRD, as well as microhardness in order to investigate residual stress and microstructural alterations initiated by the uniaxial tensile test. Barkhausen noise emission is analysed as a function of plastic straining as well as in the direction of the exerted load and interpreted with respect to the aforementioned microstructure and stress alterations. It was found that Barkhausen noise markedly decreases along with increasing plastic straining, up to 20%, followed by a strain region in which the evolution of Barkhausen noise reaches saturation. Samples after the tensile test exhibited marked magnetic anisotropy since the Barkhausen noise emission in the direction perpendicular to the tensile stress remained less affected. Apart from the effective value of Barkhausen noise, the Barkhausen noise envelopes were also analysed.
ABSTRACT
This study investigates the microstructure, residual stress state, and the corresponding magnetic anisotropy of the ship structure samples made of S235 steel after uniaxial tensile deformation. A non-destructive magnetic technique based on Barkhausen noise is employed for fast and reliable monitoring of samples exposed to the variable degrees of plastic straining. It was found that the progressively developed plastic straining of the matrix results in an alteration of the easy axis of magnetization, stress anisotropy (expressed in residual stresses state) as well as the corresponding Barkhausen noise emission. Moreover, remarkable non-homogeneity can be found within the plastically strained region, especially when the localized plastic straining takes place.
