scholarly journals Calibration Method for Monitoring Hygro-Mechanical Reactions of Pine and Oak Wood by Acoustic Emission Nondestructive Testing

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3775
Author(s):  
Chiara Bertolin ◽  
Lavinia de Ferri ◽  
Filippo Berto

The main issue of wood is its sensitivity to Relative Humidity (RH) variations, affecting its dimensional stability, and thus leading to crack formations and propagations. In situ structural health monitoring campaigns imply the use of portable noninvasive techniques such as acoustic emission, used for real-time detection of energy released when cracks form and grow. This paper proposes a calibration method, i.e., acoustic emission, as an early warning tool for estimating the length of new formed cracks. The predictability of ductile and brittle fracture mechanisms based on acoustic emission features was investigated, as well as climate-induced damage effect, leading to a strain-hardening mechanism. Tensile tests were performed on specimens submitted to a 50% RH variation and coated with chemicals to limit moisture penetration through the radial surfaces. Samples were monitored for acoustic emission using a digital camera to individuate calibration curves that correlated the total emitted energy with the crack propagation, specifically during brittle fracture mechanism, since equations provide the energy to create a new surface as the crack propagates. The dynamic surface energy value was also evaluated and used to define a Locus of Equilibrium of the energy surface rate for crack initiation and arrest, as well as to experimentally demonstrate the proven fluctuation concept.

2021 ◽  
Author(s):  
Luis Henrique Andrade Maia ◽  
Alexandre Mendes Abrão ◽  
Wander Luiz Vasconcelos ◽  
Jánes Landre Júnior ◽  
Álisson Rocha Machado ◽  
...  

Abstract In this study, the short-time Fourier transform (STFT) technique was used to determine the wear mechanisms acting on uncoated and AlCrN-coated carbide tools and their variations during the machining process. To this end, tensile tests were performed on hardened AISI 4340 steel to characterize the acoustic emission (AE) signals and subsequently isolate the steel deformation and fracture mechanisms from the signs of tool wear during the steel turning. Machining tests were carried out using the following parameters: cutting speeds of 150, 200 and 250 m/min and feed rates of 0.10 and 0.20 mm/rev. The results demonstrate that AE signals in conjunction with STFT analysis can be used to identify abrasive wear, adhesive wear and other phenomena that occur during cutting.


2007 ◽  
Vol 353-358 ◽  
pp. 34-37
Author(s):  
Rui Cao ◽  
Jian Hong Chen ◽  
J. Zhang

Combining in-situ tensile tests with detailed observations of fracture surfaces of a two-phase TiAl alloy, the fracture process and fracture mechanisms of TiAl alloys are investigated. The results reveal that Cracks prefer to initiate and propagate along lamellar interfaces, which are the weakest link in the near fully lamellar microstructure. The interlamellar strength calculated is less than the translamellar strength. The tensile stress is the driving force for crack initiation and propagation. In specimens with a slit notch, most cracks are initiated directly from the notch root and extended along lamellar interfaces. The main crack can be stopped or deflected into a delamination mode by a barrier grain with a lamellar interface orientation deviated from the direction of crack propagation. In this case, new cracks are nucleated along lamellar interfaces of grains with favorable orientation ahead the barrier grain. The main crack and a new crack are then linked by the translamellar cleavage fracture of the barrier grain with increasing applied load. In order to extend the main crack, further increases of the applied load are needed to move the high stress region into the ligament until final fracture. The process of a new crack nucleation with a bridging ligament formation decreases the crack propagation resistance rather than increases it.


2014 ◽  
Vol 609-610 ◽  
pp. 500-503
Author(s):  
Feng Yan ◽  
Rong Xin Guo ◽  
Hai Ting Xia ◽  
Hai Yu ◽  
Yu Bo Zhang

In order to understand the fracture mechanisms of Cu/CuWCP layered composites. An in-situ experimental study was carried out to investigate the behavior of the composites under uniaxial tensile loading. The specimens were manufactured by vacuum hot-pressed sintering technique, microscopic observations displayed that the microstructure of Cu/CuWCP layered composites distribute uniformly, and have no visible defect at interface. In situ tensile tests were performed in a scanning electron microscope (SEM) and the tensile strengths, failure modes of composites were measured. From the in situ experiments, the stages of nucleation, growth and coalescence of cracks in the vicinity of particles are well observed and understood. The results indicated that microcrack initiation happens at particle agglomeration and the matrix-particle interface because bond strength is weak,. With the density of microcracks increaseing, macrocrack formed, and finally cause failure of CuWCP layer, however, the Cu layer is not fracture during the whole testing.


2012 ◽  
Vol 53 (6) ◽  
pp. 1069-1074 ◽  
Author(s):  
Mitsuharu Shiwa ◽  
Hiroyuki Masuda ◽  
Hisashi Yamawaki ◽  
Kaita Ito ◽  
Manabu Enoki

2019 ◽  
Author(s):  
Nikki Theofanopoulou ◽  
Katherine Isbister ◽  
Julian Edbrooke-Childs ◽  
Petr Slovák

BACKGROUND A common challenge within psychiatry and prevention science more broadly is the lack of effective, engaging, and scale-able mechanisms to deliver psycho-social interventions for children, especially beyond in-person therapeutic or school-based contexts. Although digital technology has the potential to address these issues, existing research on technology-enabled interventions for families remains limited. OBJECTIVE The aim of this pilot study was to examine the feasibility of in-situ deployments of a low-cost, bespoke prototype, which has been designed to support children’s in-the-moment emotion regulation efforts. This prototype instantiates a novel intervention model that aims to address the existing limitations by delivering the intervention through an interactive object (a ‘smart toy’) sent home with the child, without any prior training necessary for either the child or their carer. This pilot study examined (i) engagement and acceptability of the device in the homes during 1 week deployments; and (ii) qualitative indicators of emotion regulation effects, as reported by parents and children. METHODS In this qualitative study, ten families (altogether 11 children aged 6-10 years) were recruited from three under-privileged communities in the UK. The RA visited participants in their homes to give children the ‘smart toy’ and conduct a semi-structured interview with at least one parent from each family. Children were given the prototype, a discovery book, and a simple digital camera to keep at home for 7-8 days, after which we interviewed each child and their parent about their experience. Thematic analysis guided the identification and organisation of common themes and patterns across the dataset. In addition, the prototypes automatically logged every interaction with the toy throughout the week-long deployments. RESULTS Across all 10 families, parents and children reported that the ‘smart toy’ was incorporated into children’s emotion regulation practices and engaged with naturally in moments children wanted to relax or calm down. Data suggests that children interacted with the toy throughout the duration of the deployment, found the experience enjoyable, and all requested to keep the toy longer. Child emotional connection to the toy—caring for its ‘well-being’—appears to have driven this strong engagement. Parents reported satisfaction with and acceptability of the toy. CONCLUSIONS This is the first known study investigation of the use of object-enabled intervention delivery to support emotion regulation in-situ. The strong engagement and qualitative indications of effects are promising – children were able to use the prototype without any training and incorporated it into their emotion regulation practices during daily challenges. Future work is needed to extend this indicative data with efficacy studies examining the psychological efficacy of the proposed intervention. More broadly, our findings suggest the potential of a technology-enabled shift in how prevention interventions are designed and delivered: empowering children and parents through ‘child-led, situated interventions’, where participants learn through actionable support directly within family life, as opposed to didactic in-person workshops and a subsequent skills application.


2009 ◽  
Vol 19 ◽  
pp. s243-s249 ◽  
Author(s):  
Jun-Hyub PARK ◽  
Dong-Joong KANG ◽  
Myung-Soo SHIN ◽  
Sung-Jo LIM ◽  
Son-Cheol YU ◽  
...  

Author(s):  
Tomoya Masuyama ◽  
Takuya Ikeda ◽  
Satoshi Yoshiizumi ◽  
Katsumi Inoue

The detection of damage in early stage of fatigue is important for a reliable evaluation of gear life and strength. From this point of view, the variation of strain distribution in a tooth due to cyclic load contains useful information because the fatigue crack will initiate as a result of the accumulation of plastic strain. Meanwhile, digital image equipments are widely used in our life and the performance is in progress. We took digital pictures of cyclic loaded tooth by the digital camera and compared with the picture of no load to find displacement. The strain distribution of tooth is calculated by the correlation method using those pictures. The initiation of a micro crack is observed by the method. It is also confirmed by the detection of acoustic emission wave with higher energy. The variation of stress-strain diagram in fatigue process is presented, and this illustrates the increase of strain in the final stage of fatigue.


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