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Additive manufacturing (AM) refers to advanced technologies for building 3D objects by adding material layer upon layer using either electron beam melting (EBM) or selective laser melting. AM allows us to produce lighter and more complex parts. However, various defects are created during the AM process, which severely affect fatigue behavior. In the current research, the effects of the anisotropic microstructure in the in-plane and out-of-plane orientations and defects on the fatigue crack propagation rate (FCPR) and crack path were studied. A resonance machine was used to determine the fatigue crack propagation rate (da/dN vs. ΔK) from the near-threshold up to the final fracture, accompanied by in situ Acoustic Emission (AE) monitoring. Micro-Computerized Tomography (µCT) enabled us to characterize surface and microstructural defects. Metallography was used to determine the microstructure vs. orientations and fractography to classify the fatigue fracture propagation modes. Calculations of the local stress distribution were performed to determine the interactions of the cracks with the defects. In the out-of-plane direction, the material exhibited high fatigue fracture toughness accompanied by a slightly lower fatigue crack propagation rate as compared to in-plane orientations. The near-threshold stress intensity factor was slightly higher in the out-of-plane orientation as compared to that in the in-plane one, accompanied by a lower exponent of the Paris law regime. The threshold decreased with an increasing load ratio as expected for both orientations. The crack propagation direction that crosses the elongated grains plays an important role in increasing fatigue resistance in the out-of-plane direction. In the in-plane directions, the crack propagates parallel to the grain boundary, interacts with more defects and exhibits more brittle striations on the fracture surface, resulting in lower fatigue resistance. [ABSTRACT FROM AUTHOR]

This paper presents a data fusion approach based on digital image correlation (DIC) and acoustic emission (AE) to detect, monitor and quantify progressive damage development in reinforced concrete masonry walls (CMW) with varying types of reinforcements. CMW were tested to evaluate their structural behavior under cyclic loading. The combination of DIC with AE provided a framework for the cross-correlation of full field strain maps on the surface of CMW with volume-inspecting acoustic activity. AE allowed in situ monitoring of damage progression which was correlated with the DIC through quantification of strain concentrations and by tracking crack evolution, visually verified. The presented results further demonstrate the relationships between the onset and development of cracking with changes in energy dissipation at each loading cycle, measured principal strains and computed AE energy, providing a promising paradigm for structural health monitoring applications on full-scale concrete masonry buildings. [ABSTRACT FROM AUTHOR]

The capability to predict parameters and to develop quantitative predictive models in sub-cooled boiling flow is considerable importance to nuclear reactor safety and in many other industrial processes. Such predictions are based on heat transfer mechanisms derived from theoretical models and from experimental data on bubble dynamics from growth and motion aspects. In practice, it is essential to predict the complete boiling curve in system with specific conditions, which performs an accurate description of the boiling process, and to point out the transition between the regions. The prediction of the boiling curve is based on temperature measurements on the surface of the heating element using thermocouples or thermographic and high speed cameras [1, 2]. The accuracy of these measurements could be improved by applying acoustic emission (AE) method especially in complicated geometries. The current study adopts the AE techniques in order to examine the potential of the AE in detection of bubbles during boiling process and to point out the transition zones. Preliminary AE work has been conducted in order to determine the appropriate AE parameters, and to eliminate mechanical and electromagnetic interferences. The AE findings in terms of counts, amplitude, peak frequency, etc., as a function of the applied current, revealed the early stages of bubble formation during boiling process. The AE data also indicates the transition between the different regions of the boiling curve. The AE results were analyzed by spectrum analysis and wavelet analysis in order to determine characteristic frequencies and sequences of the water boiling processes. The AE results show a great potential to detect in situ the early stages of boiling process and can be used as an efficient tool for monitoring continuously possible boiling in industrial pipes where the boiling might be critical and damage process. [ABSTRACT FROM AUTHOR]

Carbon-carbon (C/C) composites with different densities (1.8, 1.35, 0.8 g/cm³), produced by chemical vapor infiltration (CVI) were tested mechanically under quasi-static loading in bending mode of uniform and notched beams. Acoustic emission (AE) technique was used to track the mechanical threshold parameters as well as to characterize the damage build-up profile to fracture. In both states of stress (uniform and tri-axial), threshold values detected by AE activity indicated the damage onset. The sensitivity of the AE method to the density changes was apparent by variations of the threshold values. Decreasing the density from 1.8 to 0.8 g/cm³ decreases the thresholds values (σth, KIth) from 25 to 2 MPa and from 0.8 to 0.1 MPa·m1/2, respectively. Three stages in damage evolution to fracture were observed: Stage I, with no AE activity, Stage II, gradual/linear growth in AE counts up to an abrupt jump and Stage III with exponential increase in AE counts. Similarity in profile and threshold value were found between the cumulative AE counts vs. strain data and the crack density vs. strain predicted by micro mechanical model, indicating the importance of using AE in monitoring the damage evolution in composites with regard to structural integrity aspect. Wave analysis using fast Fourier transform (FFT) and short-time fast Fourier transform (ST-FFT) points out four possible failure micro-mechanisms: multilayer cracking, breaking of fiber bundles, interfacial matrix de-bonding and micro-crack growth. Breaking of fiber bundles was found to be the major damage mechanism for the low density C/C composite. [ABSTRACT FROM AUTHOR]