Inaccessible Side Research Articles

Physics-informed deep neural network for inverse heat transfer problems in materials

Recently, physics-informed neural networks have shown great promise in providing fast, elegant solutions for inverse problems. In this work, a physics-informed neural network was developed to solve an inverse heat transfer problem through a plane wall of a conductive material where one side is subjected to unknown heat flux, while the other side is thermally insulated. Using our deep neural network, we were able to predict the temperature profiles across the whole material domain and estimate the unknown thermo-physical parameters such as the material’s thermal diffusivity as well as boundary conditions (i.e., heat flux) at the inaccessible side with high accuracy. Furthermore, the method was extended to estimate time-dependent heat flux on the inaccessible side. The predicted temperatures and estimated parameters obtained from our inverse technique are in good agreement with their corresponding exact or true values. For both time-independent and dependent heat flux at the inaccessible side, our model was shown to be very robust in predicting the unknown material properties and/or boundary conditions even from noisy experimental data. The sensitivity of the model’s predictions on the model hyperparameters has also been reported to demonstrate the capability of the proposed method. This method can be utilized for the estimation of multiple thermo-physical parameters using only a few measured data in many practical materials processing involving heat transfer.

Strengthening Foundation Slabs below Ground Water Level against Punching Shear

The paper deals with strengthening structures against punching shear with focus on strengthening of existing concrete foundation slabs. These can be slabs of basements of residential, administrative and other buildings. Also, foundations slabs placed on piles can be considered. This is very specific case of strengthening where only one surface of the structure is accessible. Strengthening is often designed using massive new bearing elements, which are space-demanding. Attention is paid to the development of technology that minimizes the resulting constraints on the surrounding area and is sufficiently effective. Inspiration is strengthening of ceiling flat slabs with additional shear reinforcement. Compared to the ceiling slabs, a larger load must be bear to the foundation structures and therefore the shear reinforcements demand larger dimensions. Mechanical expanded anchors are used for anchoring on the inaccessible side. A significant contribution of mechanical anchoring is demonstrated in the tests results which make possible more efficient design of additional punching reinforcement.

Domain derivative approach to active infrared thermography

A thin conducting plate has an inaccessible side in contact with aggressive external agents. On the other side, we are able to heat the plate and take temperature maps in laboratory conditions. Detecting and evaluating damage on the inaccessible side from thermal data requires the solution of a nonlinear inverse problem for the heat equation in the presence of suitable boundary conditions for the heat equation. We carry on this task using domain derivative and integral formulation of the corresponding boundary value problem. Under non-restrictive hypothesis, we find explicit regularized schemes for Fourier reconstruction of damages.

Increased Efficiency of Surface Wave Stimulation on the Inaccessible Side of a Thick Isotropic Plate with Superimposed Periodicity

Because of the growing number of applications of phononic crystals and other periodic structures, there is a renewed and growing interest in understanding the interaction of ultrasound with periodically corrugated surfaces. This paper presents a theoretical investigation of the transformation of ultrasound incident from the solid side onto a solid-liquid periodically corrugated interface. It is shown that it is possible to tailor the shape of a corrugated surface with given periodicity such that there is a significant amount of energy transformed into Scholte-Stoneley waves than if pure saw-tooth or sine-shaped surfaces were used. This permits the fabrication of periodic structures that can be patched on or engraved in body parts of a construction and enables efficient generation of Scholte-Stoneley waves. The study is performed for incident homogeneous plane waves as well as for bounded beams. Incident longitudinal waves are studied as well as incident shear waves.

Recovering unknown terms in a nonlinear boundary condition for Laplace's equation

We consider a thin metallic plate whose top side is inaccessible and in contact with a corroding fluid. Heat exchange between metal and fluid follows linear Newton's cooling law as long as the inaccessible side is not damaged. We assume that the effects of corrosion are modelled by means of a nonlinear perturbation in the exchange law. On the other hand, we are able to heat the conductor and take temperature maps of the accessible side. Our goal is to recover the nonlinear perturbation of the exchange law on the top side from thermal data collected on the opposite one (thermal imaging). In this paper, we use a stationary model, i.e. the temperature inside the plate is assumed to fulfil Laplace's equation. Hence, our problem is stated as an inverse ill-posed problem for Laplace's equation with nonlinear boundary conditions. We study identifiability and local Lipschitz stability. In particular, we prove that the nonlinear term is identified by one Cauchy data set. Moreover, we produce approximated solutions by means of an optimizational method.

Heuristic methods for the reconstruction of two corrosion parameters from incomplete boundary data in a thin rectangular domain

This paper deals with the construction of effective heuristic methods for investigating the effect of corrosion on the inaccessible side of a thin metallic plate. In particular, we derive explicit formulas for the Thin Plate Approximation of the positive functions γ and θ that, in our model, describe energy dispersion and material loss respectively.

Influence of Wall Thickness on the Ultrasonic Evaluation of Small Closed Surface Cracks and Quantitative NDE

A new ultrasonic evaluation method has been developed for the quantitative characterization of smaller tight cracks under no load condition. In this approach, the ultrasonic testing is considered as an inverse problem to determine simultaneously the crack size and the extent of crack closure. The present paper is on the analysis of the influence of wall thickness on the evaluation of closed surface cracks from the inaccessible side of the wall. Based on experimental observation, the evaluation algorithm has been extended for the characterization of cracks with different wall thickness from the measured angle beam response. Evaluated results of both open and tightly closed small cracks with different wall thicknesses verify the method as a powerful tool for detecting and characterizing small surface cracks quantitatively.

An improved potential drop method for measuring and monitoring defects in metallic structures

In the developed form described the direct current potential drop method is a reliable and relatively accurate procedure for the measuring and surveillance of surface cracks in metallic materials. There are also significant possibilities in practice of surveying cracks on the inaccessible side of the structure. The basis for the improvement in accuracy, in particular for short cracks, is firstly an improved measuring technique and secondly calibration curves determined using an electrolytic tank. Practical experience gained in conventional plants is to date positive. The opportunity exists of benefitting from the advantages that would be brought about by an increased use of the potential drop method in plant surveillance. In nuclear plants specifically this would achieve a reduction in the testing personnel's exposure to radiation.

Acoustic emission technique for leak detection in an end shield of a pressurised heavy water reactor

This paper discusses the successful application of the Acoustic Emission Technique (AET) for detection and location of leak paths present on the inaccessible side of an end shield of a Pressurised Heavy Water Reactor (PHWR). The methodology was based on the fact that air and water leak AE signals have different characteristic features. Baseline data was generated from a sound end-shield of a PHWR for characterizing the background noise. A mock up end-shield system with saw cut leak paths was used to verify the validity of the methodology. It was found that air leak signals under pressurisation (as low as 3 psi) could be detected by frequency domain analysis. Signals due to air leaks from various locations of a defective end-shield were acquired and analysed. It was possible to detect and locate leak paths. Presence of detected leak paths were further confirmed by alternate test.

Acoustic emission technique for leak detection in an end shield of a pressurised heavy water reactor

This paper discusses a successful application of the Acoustic Emission Technique (AET) for the detection and location of leak paths present on an inaccessible side of an end shield of a Pressurised Heavy Water Reactor (PHWR). The methodology was based on the fact that air- and water-leak AE signals have different characteristic features. Baseline data was generated from a sound end shield of a PHWR for characterising the background noise. A mock-up end shield system with saw-cut leak paths was used to verify the validity of the methodology. It was found that air-leak signals under pressurisation (as low as 3 psi) could be detected by frequency domain analysis. Signals due to air leaks from various locations of defective end shield were acquired and analysed. It was possible to detect and locate leak paths. The presence of detected leak paths was further confirmed by an alternative test.