Narrow Cracks Research Articles

A Q&A with Wang Anyi

WORLDLIT.ORG 43 One day, I accidentally wandered into an old longtang . Squeezed into a narrow crack between glass-walled skyscrapers, it was nothing but a vestigial segment. I looked around in a daze—I had no idea where I was, and I had to ask directions from an elderly man who just happened to be walking by. He’d been lost in thought, and when I called out to him, he jumped: “You scared the wits out of me!” He spoke with the same local accent I’d been surrounded by growing up—genuine Shanghainese , with his hun sounding like huo, so he gave me a bit of a surprise as well. The various sounds and scents of the lane welled up from the pavement and enfolded me, hot tears filled my eyes, and the obscure pathway that had been hidden deep beneath the surface sparkled for a moment in the blazing sun, before it once again sank back into the broken tiles of a dilapidated garden wall. Memories of experiences that were attached to physical things beckoned like objects in a lost and found, but only for an instant; for immediately afterward, with another sweep of the hand, they abandoned me. The day I left home as a young woman, I went to the freight-train depot on the edge of town. There was no platform. The ties and coarse gravel beneath them lay in plain view, black rails meandered into the far distance, and heaven and earth seemed infinitely high and wide. Those who had come to see us off stood beside the wheels of the carriages and reached up through the windows, just barely able to grasp the hands of those who were leaving. At that moment, the town suddenly seemed bold and fierce as it threw off its old habits, leapt out of its old rut, and assumed a new form. When the train sped forward, the city revealed its whole face. It seemed entirely possible that there was nothing standing between the spot where we had lived, off the beaten track, filled with nooks and crannies, and the wider world. I opened my eyes wide and saw that this city was just a little courtyard, overgrown with foxtails and plantagos, a tiny and desolate patch—and yet to me it seemed vast and teeming with life. An oleander extended its flowering twigs over the wall, and green loquats fell from a neighbor’s tree—this was my season of blossoming and harvesting. Pill bugs and earthworms multiplied in the poor, thin soil of this garden. Bounded by walls on four sides, this spot also provided space for human activity, a place for me to grow, until one day I discovered that it had become the ruins of an illusion. Translation from the Chinese By Andrea Lingenfelter A Q&A with Wang Anyi by Ping Zhu Q: Would you like to be called a “woman writer” or just a “writer”? A: When I was young, I didn’t like the title “woman writer”; but now I’ve accepted it, because that is what I am. Q: Which is your favorite period of Shanghai? A: I grew up and live in Shanghai, so it is a place I cannot view objectively. Because my experiences are connected to Shanghai, it is more about which period of my life, rather than which period of Shanghai, that I like most. In the 1980s, I was young, but there were a lot of problems in my life. Now I live a comfortable life, but I’m no longer young. Q: It seems that the longtangs in your works represent not only the unique urban layout of Shanghai but also its complex history. Are the longtangs both spatial and temporal? A: Novelists are not responsible for reality. The longtangs are a stage I set up for my fictional characters. Whether the longtangs are temporal or spatial, they are theatrical. Q: What constantly drives you to break through your limits so you can produce works with different styles? A: My love for imagination and words. I don’t think I’ve had breakthroughs; I just keep writing day by day. Q: Which work have...

A Q&A with Wang Anyi

WORLDLIT.ORG 43 One day, I accidentally wandered into an old longtang . Squeezed into a narrow crack between glass-walled skyscrapers, it was nothing but a vestigial segment. I looked around in a daze—I had no idea where I was, and I had to ask directions from an elderly man who just happened to be walking by. He’d been lost in thought, and when I called out to him, he jumped: “You scared the wits out of me!” He spoke with the same local accent I’d been surrounded by growing up—genuine Shanghainese , with his hun sounding like huo, so he gave me a bit of a surprise as well. The various sounds and scents of the lane welled up from the pavement and enfolded me, hot tears filled my eyes, and the obscure pathway that had been hidden deep beneath the surface sparkled for a moment in the blazing sun, before it once again sank back into the broken tiles of a dilapidated garden wall. Memories of experiences that were attached to physical things beckoned like objects in a lost and found, but only for an instant; for immediately afterward, with another sweep of the hand, they abandoned me. The day I left home as a young woman, I went to the freight-train depot on the edge of town. There was no platform. The ties and coarse gravel beneath them lay in plain view, black rails meandered into the far distance, and heaven and earth seemed infinitely high and wide. Those who had come to see us off stood beside the wheels of the carriages and reached up through the windows, just barely able to grasp the hands of those who were leaving. At that moment, the town suddenly seemed bold and fierce as it threw off its old habits, leapt out of its old rut, and assumed a new form. When the train sped forward, the city revealed its whole face. It seemed entirely possible that there was nothing standing between the spot where we had lived, off the beaten track, filled with nooks and crannies, and the wider world. I opened my eyes wide and saw that this city was just a little courtyard, overgrown with foxtails and plantagos, a tiny and desolate patch—and yet to me it seemed vast and teeming with life. An oleander extended its flowering twigs over the wall, and green loquats fell from a neighbor’s tree—this was my season of blossoming and harvesting. Pill bugs and earthworms multiplied in the poor, thin soil of this garden. Bounded by walls on four sides, this spot also provided space for human activity, a place for me to grow, until one day I discovered that it had become the ruins of an illusion. Translation from the Chinese By Andrea Lingenfelter A Q&A with Wang Anyi by Ping Zhu Q: Would you like to be called a “woman writer” or just a “writer”? A: When I was young, I didn’t like the title “woman writer”; but now I’ve accepted it, because that is what I am. Q: Which is your favorite period of Shanghai? A: I grew up and live in Shanghai, so it is a place I cannot view objectively. Because my experiences are connected to Shanghai, it is more about which period of my life, rather than which period of Shanghai, that I like most. In the 1980s, I was young, but there were a lot of problems in my life. Now I live a comfortable life, but I’m no longer young. Q: It seems that the longtangs in your works represent not only the unique urban layout of Shanghai but also its complex history. Are the longtangs both spatial and temporal? A: Novelists are not responsible for reality. The longtangs are a stage I set up for my fictional characters. Whether the longtangs are temporal or spatial, they are theatrical. Q: What constantly drives you to break through your limits so you can produce works with different styles? A: My love for imagination and words. I don’t think I’ve had breakthroughs; I just keep writing day by day. Q: Which work have...

Simulation-based evaluation of surface micro-cracks and fracture toughness in high-speed grinding of silicon carbide ceramics

Surface/subsurface crack during grinding limits the application of engineering ceramics. High-speed grinding is proposed in ceramics grinding for high material removal rate and surface quality. The dynamic fracture toughness of ceramic materials is established by combining the Johnson-Holmquist 2 damage model for brittle material and the Griffith fracture theory. Single-grit simulation was utilized to investigate the individual crack generation and propagation in silicon carbide (SiC) indentation and engagement under different wheel surface speed. The indentation simulation results indicate that high-speed grinding enhances the SiC plastic deformation in the contact zone. Engagement simulation shows that the micro-crack transforms from deep and narrow longitudinal crack in the subsurface to shallow and width lateral crack on the surface when the wheel surface speed increases with a constant maximum undeformed chip thickness. To validate this model, the high-speed grinding experiments are conducted. The trends of micro-crack evolution, single grit force, and surface roughness of the experimental results at the constant workpiece feed rate match well with the simulation results.

Effect of steel fibers on the shear behavior of high strength concrete beams

Shear failure of reinforced concrete beams is generally affected by a large number of parameters among which the a/d ratio (shear-span/effective depth) is the most important. The other main parameters are the compressive strength, the longitudinal reinforcement ratio, the aggregate and the presence of transverse stirrups. The addition of steel fibers as reinforcement could be another parameter which contributes to the shear resistance. Such shear contribution will be assessed qualitatively and quantitatively for high strength concrete in the present work.Twenty four steel fiber reinforced high strength concrete beams without stirrups and with stirrups were tested in bending under two concentrated loads; the concrete beams were designed to have a pronounced shear behavior. The possibility of replacing traditional transverse reinforcement by steel fibers was studied. In this sense, the main testing parameters were the volume fraction of steel fibers, the aspect ratio of fibers and the presence of stirrups; five volume fractions of fibers were used (0%; 0.5%; 1.0%; 2.0% and 3.0%), with two aspect ratios (lf/df of 65 and 80). The experimental results show that the shear behavior of the fiber reinforced high strength concrete beams without stirrups is similar, if not better, to that of high strength concrete beams containing stirrups reinforcement. The fiber reinforced beams had very narrow diagonal cracks and improved shear strengths, particularly for fiber fractions from 1% to 3%. Based on the present experimental work, a new empirical model is proposed for the contribution of the fibers to the shear strength of high strength concrete beams. The proposed model was assessed against other existing models and against varied experimental data taken from the literature and found relatively more satisfactory.

Self-sealing of cracks in concrete using superabsorbent polymers

Cracks in concrete can self-heal when exposed to prolonged wetting, but this is limited to narrow cracks. In practice, cracks>0.2mm cause leakage and impair performance of structures. The potential of superabsorbent polymers (SAPs) to self-seal such cracks was investigated via transport experiments, microscopy and modelling. Forty samples containing SAP and through-thickness cracks were subjected to 0.12wt.% NaCl at 4m/m pressure gradient to simulate groundwater seepage. Results show that SAP can re-swell and seal cracks, for example in the case of 0.3mm cracks reducing peak flow rate and total flow by 85% and 98% respectively. Increasing SAP dosage accelerates sealing, but imparts a strength penalty and this limits practical applications. Modelling suggests that the effectiveness of SAP can be enhanced by increasing its re-swelling ratio and particle size, and depressing its initial swelling. These variables increase the SAP exposed in a crack and the gel volume available to seal it.

Study on heat transfer process during leaks of high pressure argon through a realistic crack

This paper proposes a method for simulating the heat transfer process of high pressure argon gas leaking through a narrow crack which causes the Joule-Thomson cooling effect (JT cooling effect). A once-through (decoupled) model was developed to firstly calculate the gas pressure drop at different crack depth, followed by the temperature drop. A MATLAB code was also developed to iteratively calculate the properties of leaking gas in a crack which was fitted as formula as boundary conditions in heat transfer simulation in COMSOL program. The simulated lowest temperature of the test plate in the vicinity of the crack is 13.8 °C after decreasing from the temperature of 30 °C with initial argon gas pressure of 91 bar. An experiment test rig designed and tested under the same conditions showed a good agreement between the simulation and experiment at the obtained lowest temperature in the test plate. The method is useful for predicting the lowest temperature in the vicinity of the crack caused by the JT cooling effect.

Study of TBM cutterhead fatigue damage mechanisms based on a segmented comprehensive failure criterion

The cutterhead endures strong, multi-point distributed impact loads when the full face rock tunnel boring machine (TBM) tunnels, which leads to intense vibration and fatigue fracture. Accordingly the structure should meet the requirement of service life considering the fracture failure at weak locations. Hence, cutterhead damage mechanism is crucial to predict and analyze residual life of a operational cutterhead under impact loads. This paper combines with the characteristics of cutterhead life, Paris model and damage cumulative theory, proposes a new failure criterion for the long thick plate in complex stress states, and establishes a segmented crack propagation life prediction model, based on the existing multi-degree-of-freedom coupling dynamic TBM cutterhead model and fatigue crack propagation prediction method for large and complex structures. Meanwhile, a physical fatigue damage test of cutterhead specimens is carried out to validate the theoretical model. Then a TBM cutterhead in a water tunnel project is taken as an example, to calculate the fatigue crack propagation and analyze how different parameters affect fatigue life. The results of the analyses reveal that with fatigue crack propagation, life of actual cutterhead is 36.5km, which gives a meaningful reference for cutterhead design. In addition, the cutterhead life decreases nearly 45.2% with the initial crack depth increasing from 0.5mm to 2mm, and it is inferred that the value of initial crack depth should be controlled below 1.6mm, to ensure the service life. On the other side, the larger the crack shape ratio (a/c), the longer the fatigue life, and the cutterhead life with a round crack (a/c=1) is about 3 times with a narrow crack (a/c=0.1). Furthermore, the crack growth rate parameter m has greater influence on cutterhead life than parameter C, with C increasing 10%, the life decreases about 9%; however, the life decreases nearly 13% when m increases 1%. Then, the critical threshold values of cutterhead material parameters to meet life requirement are obtained. From the results of fatigue damage test, it can be showed that the specimens fracture quickly when the crack depth exceeds 50% of the panel thickness, and the crack shape ratio gradually increases with the loading cycles, which is consistent with the theoretical assumption, as well as the influence rules of parameters.

La gingivopériostoplastie avec substitut osseux : technique et premiers résultats

Ortho dontico-surgical coverage of alveolar crack is essential in reason of its repercussions on facial growth and implementation of children's teeth set. We proposed to realize a premature gingivo periosto plastic surgery from 4 years old by osseous substitute to lower age of alveolar cracks closure and decrease the morbidity of patients. We conducted a retrospective study over one year (January, 2012 to December, 2012), with six months postoperatively outcomes, on 23 cases of gingivo periosto plastic sugary with osseous substitute type glass by bone transplant at infantile plastic surgery service of Timone-Children teaching hospital of Marseille, France. We held 23 patients. Seventeen children, 12 boys and 5 girls presented unilateral cracks. Twenty patients required a quantity of glass bone under 1cc for the narrow cracks. Prevalence of the mucous cracks was low (4 cases on 23). Technique of gingivo periosto plastic surgery with osseous substitute is simple and our results are globally satisfactory. We observed less morbidity of the operating site. The first results of this study showed that gingivo periosto plastic surgery with osseous substitute glass bone is a simple, reliable and reproducible technique, with promising results. Reduction of site's morbidity by osseous transplant, accessibility of glass bone cost and simplicity of surgical gesture justified adoption of this technique.

A computational framework for the simulation of high‐speed multi‐material fluid–structure interaction problems with dynamic fracture

SummaryA robust computational framework for the solution of fluid–structure interaction problems characterized by compressible flows and highly nonlinear structures undergoing pressure‐induced dynamic fracture is presented. This framework is based on the finite volume method with exact Riemann solvers for the solution of multi‐material problems. It couples a Eulerian, finite volume‐based computational approach for solving flow problems with a Lagrangian, finite element‐based computational approach for solving structural dynamics and solid mechanics problems. Most importantly, it enforces the governing fluid–structure transmission conditions by solving local, one‐dimensional, fluid–structure Riemann problems at evolving structural interfaces, which are embedded in the fluid mesh. A generic, comprehensive, and yet effective approach for representing a fractured fluid–structure interface is also presented. This approach, which is applicable to several finite element‐based fracture methods including inter‐element fracture and remeshing techniques, is applied here to incorporate in the proposed framework two different and popular approaches for computational fracture in a seamless manner: the extended FEM and the element deletion method. Finally, the proposed embedded boundary computational framework for the solution of highly nonlinear fluid–structure interaction problems with dynamic fracture is demonstrated for one academic and three realistic applications characterized by detonations, shocks, large pressure, and density jumps across material interfaces, dynamic fracture, flow seepage through narrow cracks, and structural fragmentation. Correlations with experimental results, when available, are also reported and discussed. For all four considered applications, the relative merits of the extended FEM and element deletion method for computational fracture are also contrasted and discussed. Copyright © 2015 John Wiley & Sons, Ltd.

Permeability and thermal cracking at pressure in Sioux Quartzite

Abstract We heated specimens of Sioux Quartzite to 683, 783 and 830 K at confining pressures ( P c ) of 0.1, 100 and 200 MPa. Following the heat treatments, we measured the permeability under confining pressures that varied from 170 MPa to 60 MPa, with pore-fluid pressures of 10, 16 or 22 MPa, resulting in tests having effective pressures ranging from 36 to 160 MPa. When measured under those effective pressures, the permeability of samples with microstructures formed by cracking at 683–830 K and atmospheric pressure increased by a factor of 3–4. Scanning electron microscopy (SEM) shows that thermal cracking increases the number of long, narrow cracks, qualitatively explaining the increased sensitivity of permeability to low effective pressure. Fracture mechanics models suggest that confining pressures lower the stress intensity factors to well below the critical value for crack propagation, and the absence of many long cracks is consistent with that prediction. At P c =200 MPa, thermal cracking during the heat treatment is suppressed. Although the heating experiments were performed on nominally dry samples, in samples heated at the highest temperatures SEM revealed microstructural features that are similar to those seen in crack healing experiments.

Numerical Study on the Heat Transfer in the Leakage of Pressure Vessels Considering the Joule-Thomson Cooling Effect

The cooling effect caused by the Joule-Thomson (JT) effect in the leakage of pressure vessels has gained more and more attention and worries from natural gas transportation industries as it may influence the validity of the conventional leak-before-break approach. Currently, leak-before-break (LBB) design codes for pressure vessels do not take into account of the subsequent low temperature depression and the drop in fracture toughness in the aftermath of a leak. This study is to ensure the integrity of the compressed natural gas (CNG) containment in marine transportation vessels being proposed to transport the gas in highly pressurized (up to 250bar) cylinders. A numerical method was proposed to simulate the heat transfer between the high pressure argon gas leaking through a narrow crack and the surrounding metal which is caused by the Joule-Thomson cooling effect of the leaking argon. A one-way coupling model was developed to calculate the gas pressure drop at different crack depth, followed by the temperature drop. A heat transfer simulation then calculated the temperature in the metal in the vicinity of the crack. The Redlich-Kwong (RK) equation with a relatively high accuracy was adopted to evaluate the temperature change of the leaking argon. The modified Petukhov correlation by Adams et al. was employed to evaluate the heat transfer coefficient of leaking argon. A MATLAB code was developed to iteratively calculate the properties of leaking gas in a crack which was fitted as formula as boundary conditions in heat transfer simulation of COMSOL program. Under the maximum internal pressure of 91bar, the simulated temperature drop of the test plate in the vicinity of the crack caused by the Joule-Thomson cooling effect is 16.2°C. An experiment rig designed and tested under the same conditions showed a good agreement between the simulation and experiment at the obtained lowest temperature in the test plate.

Elucidation of rapid reduction of water flow through concrete crack regarded as self-healing phenomenon

ID No : 75 ABSTRACT The development of self-healing concrete has witnessed several strides in the last three decades. Among these is the understanding of the mechanisms of self-healing concrete, as well as the realization of new technologies of enhancing crack selfhealing in concrete. Previous research suggests that crack closing mechanism occurs due to mainly 1) Hydration of anhydrous cement, 2) Formation and crystallization of Calcium Carbonate, 3) Swelling of cement matrix and 4) Sedimentation of particles in the crack interstices. In this research however, after a one by one investigation, it was found that these mechanisms do not fully explain the drastic water flow recovery that occurs in the initial stages of water permeation through cracked concrete. This preliminary finding then prompted direct visual observation of water flow through cracks’ narrow spaces. This was achieved by using acrylic resin and glass as transparent media over the concrete surface of split and machine cut cracks respectively. With this, an interesting observation was made – the creation of air bubbles (waterless spaces inside the interstices) following the condition of full water saturation. It was observed that water flow through the narrow crack openings creates air bubbles by probably various water action mechanisms. The created air bubbles narrow water flow paths in the crack, causing significant water flow reduction in the initial and later stages of water supply condition.

Magnetic Leakage Testing Using Linearly Integrated Hall and GMR Sensor Arrays to Inspect Inclusions in Cold-Rolled Strips

Inclusions in steel are entrapped foreign materials, which may be metallic or non-metallic; they may be distributed throughout the volume of steel strips during the rolling process and may propagate as narrow cracks in steel strips. In this paper, for inspecting inclusions in steel strips, we propose the use of magnetic flux leakage testing involving a magnetizer and magnetic field sensor arrays, such as linearly integrated Hall sensors (LIHaS) in differential mode and linearly integrated giant magnetoresistance sensors (LIGiS). In the proposed method, images of the distribution of Hall voltage (V H ) and giant magnetoresistance voltage (V G ) due to the magnetic leakage field around an inclusion are obtained by means of LIHaS and LIGiS, respectively. The magnetic leakage field images are obtained at different magnetization directions relative to the rolling direction by rotating the magnetizer. Different data processing techniques, such as differentiation, noise reduction, and fusion of image data of the inclusion obtained by LIHaS and LIGiS, are applied to enhance the detectability of the inclusion. The effectiveness of the proposed technique was experimentally verified by detecting actual inclusions situated in the rolling direction in a cold-rolled steel strip.

Vertical cracks characterization using lock-in thermography: II finite cracks

The aim of this work is to characterize vertical cracks of finite size and arbitrary shape using optically excited lock-in thermography. In the first place, we have solved the direct problem, which consists of calculating the surface temperature distribution when the shape, size and width of the vertical crack are known. To do this we have developed a new method based on discontinuous finite elements, which allows one to deal even with very narrow cracks, for which classical finite element methods fail. The surface temperature of steel samples containing semi-infinite cracks and illuminated with a laser beam focused close to the crack has been measured using a lock-in thermography setup. A least square fit of the amplitude and phase of the surface temperature is used to retrieve the width and depth of the semi-infinite crack. A very good agreement between the nominal and retrieved values of both parameters is found, confirming the validity of the model.

Leak rates of high pressure steam–water across simulation crack

This paper presents a critical leak flow from a simulated crack under the fluid condition of high-pressure water–steam and supercritical water. An experimental study of critical leak flow has been performed at Xi’an Jiao tong University (XJTU) with a rhomboid crack and two narrow circular cracks, which could be applied in the leak-before-break (LBB) analysis. A rhomboid crack with an opening displacement of 140μm and two circle cracks with diameters of 1mm and 1.84mm were performed in the experiments. Pressure drop and flow rates were measured to analyze the flow characteristics. Experimental parameters covered pressures up to 23MPa and temperatures up to 400°C. The results were compared with the theory of Henry’s non-equilibrium subcooled two-phase critical flow in long tubes. It was found that the Henry’s Homogeneous Non-Equilibrium Model (HHNM) could be extended to predict supercritical fluid critical flow when temperature is lower than the pseudocritical point. A modified 1-D adiabatic friction-choked flow model was developed to upstream superheated steam and supercritical water when temperature is higher than the pseudocritical point. It was found that the predictions of the modified 1-D adiabatic friction-choked flow model agreed well with the present experimental data.

A feed-through ACFM probe with sensor array for pipe string cracks inspection

Pipe string is highly susceptible to cracks caused by stress corrosion and fatigue damage in petroleum industry. The performance of existing magnetic flux leakage and magnetic particle inspection is inadequate to detect narrow axial cracks in pipe string. Results obtained from crack inspection simulations and experiments using a novel feed-through alternating current field measurement (ACFM) probe presented in this paper suggest that this probe can be adopted for an accurate, rapid and non-contacting detection of pipe string cracks. A structure of equal-spaced sensor array of this feed-through ACFM probe is applied to scan the full circumference of pipe string simultaneously in a single pass.

Non-destructive testing of inclusions in cold-rolled strip steels using hall and giant magnetoresistance sensor arrays

Inclusions in steel are entrapped foreign materials, which may be metallic or non-metallic. The inclusions disrupt the structural homogeneity of the steel and affect its mechanical properties. Moreover, nonmetallic inclusions such as calcium and magnesium can be propagated as narrow cracks in steel strips after the rolling process. In this paper, we propose the use of magnetic flux leakage testing involving the fusion of images obtained by arrays of linearly integrated Hall sensors (LIHaS) and linearly integrated giant magnetoresistance sensors (LIGiS) for inspecting inclusions in steel strips. In the proposed method, the normal (Bz) and tangential (Bx) components of the magnetic leakage field around an inclusion are detected by means of LIHaS and LIGiS,respectively. The images of the magnetic leakage fieldwere obtained at different scanning (magnetization) directions relative to the rolling direction. The Bz and Bx images of the inclusion are then combined by using image fusion technique to enhance the detection of the inclusion. The effectiveness of the proposed image fusion technique was experimentally verified by using LIHaS and LIGiS images of an inclusion in a cold-rolled steel strip.

Trapped modes due to narrow cracks in thin simply-supported elastic plates

We consider an elastic plate of infinite length and constant width supported simply along its two parallel edges and having a finite length crack along its centreline. In particular, we look for and find trapped modes (localised oscillations) in the presence of the crack. An explicit wide-spacing approximation based on the Wiener–Hopf technique applied to incident wave scattering by semi-infinite cracks is complemented by an exact formulation of the problem in the form of integro-differential equations. An application of a Galerkin method for the numerical calculation of results from the latter method leads to a novel explicit ‘small-spacing’ approximation. In combination with the wide-spacing results this is shown to provide accurate results for all lengths of crack.

Coupled approach VIM–BEM for efficient modeling of ECT signal due to narrow cracks and volumetric flaws in planar layered media

Rapid and accurate modeling of Eddy Current Testing (ECT) signal is required in many industrial areas. For example, crack detection via ECT is widely employed in aeronautics and aerospace industry to inspect riveted planar multilayered structures. In these structures, small narrow cracks (e.g. micro-cracks) may initiate at the edge of rivet holes (which can be considered as large volumetric flaws) and propagate through the PMS. This paper proposes a new and efficient model, based on a coupled approach between Volume Integral Method (VIM) and Boundary Element Method (BEM), simulating ECT probe signals due to the presence of both narrow cracks located near volumetric flaws within a given PMS. Simulation results are compared with experimental and simulated signals obtained with a numerical code. The performance of the method, in terms of accuracy and computational time, is discussed and the perspectives opened are presented.

Defects-Induced Hot Spots in TATB

We investigate the interaction between the laser and energetic materials with different defects. The three-dimensional models of triaminotrinitrobenzene (TATB) explosives containing spherical pores, craters, and cracks are established, respectively. The laser ignition process of TATB is simulated with three-dimensional finite difference time domain (3D-FDTD) method to study the electromagnetic field distribution surrounding these defects with 355 nm laser incidence. It indicates that the larger defects in the TATB energetic materials have the stronger electric field modulations to initial incident laser for all the three defects, which is easier to lead to the generation of hot spots. Furthermore, TATB materials with spherical pore defects and crater defects are easier to form hot spots than those with narrow crack defects.