Experimental Investigation on the Crack Closure Phenomenon Using Barkhausen Noise Method G. Donzella 1 & L. Solazzi 1 & C. Petrogalli 1 Received: 25 October 2016 /Accepted: 20 September 2017 /Published online: 27 September 2017 # The Society for Experimental Mechanics, Inc 2017 Abstract This paper presents an experimental investigation on a middle tension (MT) specimen made of a low carbon structural steel subjected to cyclic loading. The work was aimed to assess the effectiveness of Barkhausen Noise method in detecting the crack closure phenomenon. The Influence of probe orientation and position ahead the crack tip was exam- ined, in order to optimize the magnetic measurements. A fil- tering procedure was also used to treat the Barkhausen Noise signal. A procedure was proposed to determine the crack- opening load from it. On the same specimen, some strain gauge measurements were carried out to determine the crack-opening load by the local compliance method. The re- sults showed a good agreement of the results obtained with the two experimental techniques. Keywords Crack closure . Barkhausen noise . Crack opening load . Fracture mechanics Introduction The Barkhausen Noise (BN) is a non-destructive technique whose use has progressively increased in several industrial fields [1]. Sensitivity of BN to stress level and several micro-structural features, like dislocations network, grain boundaries density, second phase precipitates, texture and cavities make this method extremely versatile for material characterization [2–9]. In particular, several researches have been carried out in order to assess the Barkhausen noise method suitability in char- acterizing and monitoring the fatigue damage. The base of this type of analysis is the BN sensitivity to the fatigue induced changes in micro-structural features and in the stress-strain hys- teresis loop (i.e. hardening/softening phenomenon) and to the subsequent crack nucleation and propagation. High and low cycle fatigue tests under controlled stress and strain were car- ried out on different materials by measuring BN intensity in the time domain as a function of cycle number [10–18]. In this way, the variations of magnetic parameters can be detected, related to material microstructural changes, and, in some cases, the different stages of the fatigue process can be recognized, i.e. initial arrangement, stabilization, crack nucle- ation and propagation, [19–23]. The purpose of this work is to apply the BN method to determine and quantify the phenomenon of crack closure. As known, during cyclic loading, the two surfaces of crack come into contact at low but non-zero load value. This phenomenon is controlled by several parameters, as the oxidation and roughness and irregularity of the crack sur- faces, crack tip plasticity and cycle ratio [24]. The correct comprehension and evaluation of crack closure have been pointed to be necessary to improve the standard tools used to predict cracks growth. In particular, the opening load (defined as the minimum load necessary to open the crack), is the key information for the correct determination of the effective stress intensity range value Keff which con- trols the crack growth rate [25, 26]. The opening load is com- monly measured by the compliance method, which is also included in an ASTM standard for material fatigue character- isation [27]; several procedures for the processing refinement of global displacement or local strain measurements carried out with this method were progressively developed and ded- icated algorithms were introduced for this aim [28, 29]. * L. Solazzi luigi.solazzi@unibs.it 1 Department of Mechanical and Industrial Engineering, University of Brescia, via Branze 38, 25123 Brescia, Italy Exp Tech (2017) 41:605–613 DOI 10.1007/s40799-017-0210-5