Imperial College London


Faculty of EngineeringDepartment of Mechanical Engineering

Non-Destructive Evaluation Research Fellow







563City and Guilds BuildingSouth Kensington Campus





Publication Type

19 results found

Li S, Huang M, Song Y, Lan B, Li Xet al., 2024, Ultrasonic backscattering model for Rayleigh waves in polycrystals with Born and independent scattering approximations, Ultrasonics, Vol: 140, ISSN: 0041-624X

This paper presents theoretical and numerical models for the backscattering of 2D Rayleigh waves in single-phase, untextured polycrystalline materials with statistically equiaxed grains. The theoretical model, based on our prior inclusion-induced Rayleigh wave scattering model and the independent scattering approximation, considers single scattering of Rayleigh-to-Rayleigh (R-R) waves. The numerical finite element model is established to accurately simulate the scattering problem and evaluate the theoretical model. Good quantitative agreement is observed between the theoretical model and the finite element results, especially for weakly scattering materials. The agreement decreases with the increase of the anisotropy index, owing to the reduced applicability of the Born approximation. However, the agreement remains generally good when weak multiple scattering is involved. In addition, the R-R backscattering behaviour of 2D Rayleigh waves is similar to the longitudinal-to-longitudinal and transverse-to-transverse backscattering of bulk waves, with the former exhibiting stronger scattering. These findings establish a foundation for using Rayleigh waves in the quantitative characterisation of polycrystalline materials.

Journal article

Tian Y, Zhao Y, Kang Y, Wu J, Meng Y, Hu X, Huang M, Lan B, Kang F, Li Bet al., 2024, Quantum chemical calculation study on the thermal decomposition of electrolyte during lithium-ion battery thermal runaway, Frontiers in Energy Research, Vol: 12, ISSN: 2296-598X

Understanding the behavior of lithium-ion battery electrolytes during thermal runaway is essential for designing safer batteries. However, current reports on electrolyte decomposition behaviors often focus on reactions with electrode materials. Herein we use quantum chemical calculations to develop a model for the thermal decomposition mechanism of electrolytes under both electrolyte and ambient atmosphere conditions. The thermal stability is found to be associated with the dielectric constants of electrolyte constituents. Within the electrolyte, the solvation effects between molecules increase electrolyte stability, making thermal decomposition a more difficult process. Furthermore, Li+ is observed to facilitate electrolyte thermal decomposition, as the energy required for the thermal decomposition reactions of molecules decreases when they are bonded with Li+. It is hoped that this study will offer a theoretical basis for understanding the complex reactions occurring during thermal runaway events.

Journal article

Katch L, Yeoh WY, Touzanov O, Pacheco M, Lan B, Arguelles APet al., 2023, Shear wave ultrasound inspection of flaws in silicon wafers using focused transducers, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 70, Pages: 1506-1515, ISSN: 0885-3010

Silicon parts can contain micrometer-sized vertical cracks that are challenging to detect. Inspection using high-frequency focused ultrasound has shown promise for detecting defects of this size and geometry. However, implementing focused ultrasound to inspect anisotropic media can prove challenging, given the directional dependence of wave propagation and subsequent focusing behavior. In this work, back surface-breaking defects at various orientations within silicon wafers (0°, 15°, and 45° relative to the [010] crystallographic axis) are experimentally inspected in an immersion tank setup. Using 100 MHz unfocused and focused shear waves, the impact of medium anisotropy on focusing and defect detection is evaluated. The scattering amplitude and defect detection sensitivity results demonstrate orientation-dependent patterns that strongly rely on the use of focused transducers. The defects along the 45° orientation reveal two-lobe scattering patterns with maximum amplitudes less than half that of the defects in the 0° orientation, which in contrast show a one-lobe scattering pattern. The experimental results are further explored using finite element (FE) modeling and ray tracing to visualize the impact of focusing on wave propagation within the silicon. Ray tracing results show that the focused beam profiles for the 45° and 0° orientations form a butterfly wing and elliptical focusing profile, respectively, which correspond directly to experimentally found scattering patterns from defects. Additionally, the FE scattering results from unfocused transducers reveal single lobe scattering for both 0° and 45° orientations, proving the varying scattering patterns to be driven by the anisotropic focusing behavior.

Journal article

Huang M, Cegla F, Lan B, 2023, Stiffness matrix method for modelling wave propagation in arbitrary multilayers, International Journal of Engineering Science, Vol: 190, ISSN: 0020-7225

Natural and engineered media usually involve combinations of solid, fluid and porous layers, and accurate and stable modelling of wave propagation in such complex multilayered media is fundamental to evaluating their properties with wave-based methods. Here we present a general stiffness matrix method for modelling waves in arbitrary multilayers. The method first formulates stiffness matrices for individual layers based on the governing wave equations for fluids and solids, and the Biot theory for porous materials. Then it utilises the boundary conditions considered at layer interfaces to assemble the layer matrices into a global system of equations, to obtain solutions for reflection and transmission coefficients at any incidence. Its advantage over existing methods is manifested by its unconditional computational stability, and its validity is proved by experimental validations on single solid sheets, porous layers, and porous-solid-porous battery electrodes. This establishes a powerful theoretical platform that allows us to develop advanced wave-based methods to quantitatively characterise properties of the layers, especially for layers of porous materials.

Journal article

Yeoh WY, Lan B, Lowe MJS, 2023, Investigation of the influence of macrozones in titanium alloys on the propagation and scattering of ultrasound, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 479, ISSN: 1364-5021

The presence of macrozones (or micro-textured regions) in Ti-6Al-4V (Ti-64) was shown to be a potential cause to the onset of cold dwell fatigue which reduces fatigue life significantly. Past research has demonstrated the potential of using ultrasonic testing for macrozone characterization, with the variation of ultrasound attenuation, backscatter and velocity in the presence of macrozones. However, due to the complexity of the microstructure, some physical phenomena that were observed are still not well understood. In this study, we propose the use of finite-element polycrystalline models to provide us with a means to systematically study the wave-macrozone interaction. Through this investigation performed using two-dimensional models, we are able to identify important correlations between macrozone characteristics (size, shape and texture) and ultrasound responses (attenuation, backscatter and velocity). The observed behaviours are then validated experimentally, and we also highlight how this understanding can potentially aid with the characterization of macrozones in Ti-64 samples.

Journal article

Li S, Huang M, Song Y, Lan B, Li Xet al., 2023, Theoretical and numerical modeling of Rayleigh wave scattering by an elastic inclusion, Journal of the Acoustical Society of America, Vol: 153, Pages: 2336-2350, ISSN: 0001-4966

This work presents theoretical and numerical models for the backscattering of two-dimensional Rayleigh waves by an elastic inclusion, with the host material being isotropic and the inclusion having an arbitrary shape and crystallographic symmetry. The theoretical model is developed based on the reciprocity theorem using the far-field Green's function and the Born approximation, assuming a small acoustic impedance difference between the host and inclusion materials. The numerical finite element (FE) model is established to deliver a relatively accurate simulation of the scattering problem and to evaluate the approximations of the theoretical model. Quantitative agreement is observed between the theoretical model and the FE results for arbitrarily shaped surface/subsurface inclusions with isotropic/anisotropic properties. The agreement is excellent when the wavelength of the Rayleigh wave is larger than, or comparable to, the size of the inclusion, but it deteriorates as the wavelength gets smaller. Also, the agreement decreases with the anisotropy index for inclusions of anisotropic symmetry. The results lay the foundation for using Rayleigh waves for quantitative characterization of surface/subsurface inclusions, while also demonstrating its limitations.

Journal article

Bikos D, Samaras G, Cann P, Masen M, Hardalupas I, Vieira J, Hartmann C, Huthwaite P, Lan B, Charalambides Met al., 2023, Destructive and non-destructive mechanical characterisation of chocolate with different levels of porosity under various modes of deformation, Journal of Materials Science, Vol: 58, Pages: 5104-5127, ISSN: 0022-2461

Chocolate exhibits a complex material response under the varying mechanical loads present during oral processing. Mechanical properties such as Young’s modulus and fracture stress are linked to sensorial attributes such as hardness. Apart from this link with hardness perception, these mechanical properties are important input parameters towards developing a computational model to simulate the first bite. This study aims to determine the mechanical properties of chocolate with different levels of micro-aeration, 0–15%, under varying modes of deformation. Therefore, destructive mechanical experiments under tension, compression, and flexure loading are conducted to calculate the Young’s modulus, yield, and fracture stress of chocolate. The values of Young’s modulus are also confirmed by independent ultrasonic mechanical experiments. The results showed that differences up to 35% were observed amongst the Young’s modulus of chocolate for different mechanical experiments. This maximum difference was found to drop with increasing porosity and a negligible difference in the Young’s modulus measurements amongst the different mechanical experiments is observed for the 15% micro-aerated chocolate. This phenomenon is caused by micro-pores obstructing the microscopic inelastic movement occurring from the early stages of the material’s deformation. This work provides a deeper understanding of the mechanical behaviour of chocolate under different loading scenarios, which are relevant to the multiaxial loading during mastication, and the role of micro-aeration on the mechanical response of chocolate. This will further assist the food industry’s understanding of the design of chocolate products with controlled and/or improved sensory perception.

Journal article

Li C, Du H, Kang Y, Zhao Y, Tian Y, Wozny J, Lu J, Li T, Tavajohi N, Huang M, Lan B, Kang F, Li Bet al., 2023, Room-temperature direct regeneration of spent LiFePO4 cathode using the external short circuit strategy, Next Sustainability, Vol: 1, ISSN: 2949-8236

Lithium iron phosphate batteries (LFP), widely used as power sources, are forecasted to reach the terawatt-hour scale, inevitably leading to battery waste and expediating the urgency for effective recycling processes for LFP. The modern recycling methodologies based on material recovery face significant economic, environmental, and energy consumption challenges. This research attempts to resolve these challenges by providing direct cathode regeneration based on the principles of an external short-circuit to replenish lithium lost in the spent cathode with lithiated materials (LiC6, Li metal). Given that most active lithium loss in the cathode is caused by the growth of the solid electrolyte interphase rather than structural damage, restoring the lost lithium can revitalize a spent cathode battery’s electrochemical performance to a near-original state. The lithium loss in LFP cathodes ranging from 20% to 80% was renewed by supplementing lithium. Relithiation of 10Ah commercial LFP spent cathode showed revitalized electrochemical performance. Compared to the modern recycling methods, direct cathode regeneration improves the economic benefits of recycling by 33%, decreases energy consumption by 48%, and reduces carbon emissions by 62%. Direct cathode regeneration provides a scaffold for the next generation of recycling methods to improve recycling efficiency while reducing their environmental footprint.

Journal article

Huang M, Kirkaldy N, Zhao Y, Patel Y, Cegla F, Lan Bet al., 2022, Quantitative characterisation of the layered structure within lithium-ion batteries using ultrasonic resonance, Journal of Energy Storage, Vol: 50, Pages: 1-14, ISSN: 2352-152X

Lithium-ion batteries (LIBs) are becoming an important energy storage solution to achieve carbon neutrality, but it remains challenging to characterise their internal states for the assurance of performance, durability and safety. This work reports a simple but powerful non-destructive characterisation technique, based on the formation of ultrasonic resonance from the repetitive layers within LIBs. A physical model is developed from the ground up, to interpret the results from standard experimental ultrasonic measurement setups. As output, the method delivers a range of critical pieces of information about the inner structure of LIBs, such as the number of layers, the average thicknesses of electrodes, the image of internal layers, and the states of charge variations across individual layers. This enables the quantitative tracking of internal cell properties, potentially providing new means of quality control during production processes, and tracking the states of health and charge during operation.

Journal article

Gillespie J, Yeoh WY, Zhao C, Parab ND, Sun T, Rollett AD, Lan B, Kube CMet al., 2021, In situ characterization of laser-generated melt pools using synchronized ultrasound and high-speed X-ray imaging, Journal of the Acoustical Society of America, Vol: 150, Pages: 2409-2420, ISSN: 0001-4966

Metal additive manufacturing is a fabrication method that forms a part by fusing layers of powder to one another. An energy source, such as a laser, is commonly used to heat the metal powder sufficiently to cause a molten pool to form, which is known as the melt pool. The melt pool can exist in the conduction or the keyhole mode where the material begins to rapidly evaporate. The interaction between the laser and the material is physically complex and difficult to predict or measure. In this article, high-speed X-ray imaging was combined with immersion ultrasound to obtain synchronized measurements of stationary laser-generated melt pools. Furthermore, two-dimensional and three-dimensional finite-element simulations were conducted to help explain the ultrasonic response in the experiments. In particular, the time-of-flight and amplitude in pulse-echo configuration were observed to have a linear relationship to the depth of the melt pool. These results are promising for the use of ultrasound to characterize the melt pool behavior and for finite-element simulations to aid in interpretation.

Journal article

Parra-Raad J, Lan B, Cegla F, 2021, Orthogonally polarised shear waves for evaluating anisotropy and cracks in metals, Independent Nondestructive Testing and Evaluation (NDT and E) International, Vol: 121, ISSN: 0963-8695

The detection of crack-like defects using ultrasound is a problem widely studied by the non-destructive evaluation community. In this work, a technique of how to detect the presence of a crack-like defect and estimate its orientation in an anisotropic material by means of two orthogonal shear waves is presented. A detailed study of shear wave propagating and splitting at any incident angle, and its interaction with crack-like defects in anisotropic materials, is also presented. In this paper it is shown that by the use of two orthogonal shear waves with linear polarisation the authors could: 1) estimate the material level of anisotropy within approximately 0.5% of the measured value; 2) estimate the angular position of the principal shear directions of the material with respect to the orthogonal shear wave sources within ±5⁰ accuracy; 3) excite a shear wave purely polarised along one of the principal shear directions with two orthogonal shear waves placed at an arbitrary angular position; 4) detect the presence of a crack-like defect in an anisotropic material based on the back-wall echoes of two orthogonal shear waves, 5) estimate the orientation of a crack-like defect in an anisotropic material within ∼ ± 5⁰ of the theoretical value. The simulation and experimental results obtained show that the technique presented in this paper has potential to become an effective tool for crack-like defect detection and material characterisation.

Journal article

Lan B, Carpenter MA, Gan W, Hofmann M, Dunne FPE, Lowe MJSet al., 2018, Rapid measurement of volumetric texture using resonant ultrasound spectroscopy, Scripta Materialia, Vol: 157, ISSN: 1359-6462

This paper presents a non-destructive evaluation method of volumetric texture using resonant ultrasound spectroscopy (RUS). It is based on a general theoretical platform that links the directional wave speeds of a polycrystalline aggregate to its texture through a simple convolution relationship, and RUS is employed to obtain the speeds by measuring the elastic constants, where well-established experimental and post-processing procedures are followed. Important lower-truncation-order textures of representative hexagonal and cubic metal samples with orthorhombic sample symmetries are extracted, and are validated against independent immersion ultrasound and neutron tests. The successful deployment of RUS indicates broader applications of the general methodology.

Journal article

Lan B, 2018, Non-iterative, stable analysis of surface acoustic waves in anisotropic piezoelectric multilayers using spectral collocation method, Journal of Sound and Vibration, Vol: 433, Pages: 16-28, ISSN: 0022-460X

Surface acoustic waves (SAWs) enjoy profound importance across many disciplines, and one of their most prominent applications are the vast ranges of SAW devices made of piezoelectric multilayers. Thus a stable and efficient algorithm of analysing key SAW parameters in arbitrary layered media is of wide interest. This paper introduces such an algorithm based on the spectral collocation method (SCM). It firstly explains the fundamental governing equations and their numerical calculations via the SCM in a self-contained way, and then demonstrates the technique on the well-studied ZnO/diamond/Si material system, where the key factors of phase velocity, electromechanical coupling coefficient and effective permittivity are evaluated and discussed in detail. Compared to the widely employed root-finding approach, it is shown that the SCM is intuitive to formulate and code, and is highly accurate; it delivers all modes at once, and does not suffer from numerical instabilities. The establishment of the method on this simple example also implies potential applications to more general material and geometry types that could be difficult for the conventional approaches.

Journal article

Lan B, Britton TB, Jun T-S, Gan W, Hofmann M, Dunne F, Lowe Met al., 2018, Direct volumetric measurement of crystallographic texture using acoustic waves, Acta Materialia, Vol: 159, Pages: 384-394, ISSN: 1359-6454

Crystallographic texture in polycrystalline materials is often developed as preferred orientation distribution of grains during thermo-mechanical processes. Texture dominates many macroscopic physical properties and reflects the histories of structural evolution, hence its measurement and control are vital for performance optimisation and deformation history interogation in engineering and geological materials. However, exploitations of texture are hampered by state-of-the-art characterisation techniques, none of which can routinely deliver the desirable non-destructive, volumetric measurements, especially at larger lengthscales. Here we report a direct and general methodology retrieving important lower-truncation-order texture and phase information from acoustic (compressional elastic) wave speed measurements in different directions through the material volume (avoiding the need for forward modelling). We demonstrate its deployment with ultrasound in the laboratory, where the results from seven representative samples are successfully validated against measurements performed using neutron diffraction. The acoustic method we have developed includes both fundamental wave propagation and texture inversion theories which are free from diffraction limits, they are arbitrarily scalable in dimension, and can be rapidly deployed to measure the texture of large objects. This opens up volumetric texture characterisation capabilities in the areas of material science and beyond, for both scientific and industrial applications.

Journal article

Lan B, Lowe M, DUNNE F, 2015, A spherical harmonic approach for the determination of HCP texture from ultrasound: a solution to the inverse problem, Journal of the Mechanics and Physics of Solids, Vol: 83, Pages: 179-198, ISSN: 0022-5096

A new spherical convolution approach has been presented which couples HCP single crystal wave speed (the kernel function) with polycrystal c-axis pole distribution function to give the resultant polycrystal wave speed response. The three functions have been expressed as spherical harmonic expansions thus enabling application of the de-convolution technique to enable any one of the three to be determined from knowledge of the other two. Hence, the forward problem of determination of polycrystal wave speed from knowledge of single crystal wave speed response and the polycrystal pole distribution has been solved for a broad range of experimentally representative HCP polycrystal textures. The technique provides near-perfect representation of the sensitivity of wave speed to polycrystal texture as well as quantitative prediction of polycrystal wave speed. More importantly, a solution to the inverse problem is presented in which texture, as a c-axis distribution function, is determined from knowledge of the kernel function and the polycrystal wave speed response. It has also been explained why it has been widely reported in the literature that only texture coefficients up to 4th degree may be obtained from ultrasonic measurements. Finally, the de-convolution approach presented provides the potential for the measurement of polycrystal texture from ultrasonic wave speed measurements.

Journal article

Lan B, lowe M, dunne F, 2015, A generalized spherical harmonic deconvolution to obtain texture of cubic materials from ultrasonic wave speed, Journal of the Mechanics and Physics of Solids, Vol: 83, Pages: 221-242, ISSN: 0022-5096

In this paper, the spherical harmonic convolution approach for HCP materials (Lan et al., 2015) is extended into a generalised form for the principal purpose of bulk texture determination in cubic polycrystals from ultrasonic wave speed measurements. It is demonstrated that the wave speed function of a general single crystal convolves with the polycrystal Orientation Distribution Function (ODF) to make the resultant polycrystal wave speed function such that when the three functions are expressed in harmonic expansions, the coefficients of any one function may be determined from the coefficients of the other two. All three Euler angles are taken into account in the description of the ODF such that the theorem applies for all general crystal systems.The forward problem of predicting polycrystal wave speed with knowledge of single crystal properties and the ODF is solved for all general cases, with validation carried out on cubic textures showing strong sensitivity to texture and excellent quantitative accuracy in predicted wave speed amplitudes. Importantly, it is also revealed by the theorem that the cubic structure is one of only two crystal systems (the other being HCP) whose orientation distributions can be inversely determined from polycrystal wave velocities by virtue of their respective crystal symmetries. Proof of principle is then established by recovering the ODFs of representative cubic textures solely from the wave velocities generated from a computational model using these texture inputs, and excellent accuracies are achieved in the recovered ODF coefficients as well as the resultant pole figures. Hence the methodology is argued to provide a powerful technique for wave propagation studies and bulk texture measurement in cubic polycrystals and beyond.Keywords Texture; Generalised spherical convolution; Ultrasound; Cubic polycrystals

Journal article

Lan B, Lowe M, Dunne FPE, 2014, Experimental and computational studies of ultrasound wave propagation in hexagonal close-packed polycrystals for texture detection, Acta Materialia, Vol: 63, Pages: 107-122, ISSN: 1359-6454

Texture in hexagonal close-packed (hcp) polycrystalline metals, often developed during thermomechanical processing, affects ultrasonic wave velocity. In this study, the relationship between bulk texture and ultrasonic wave velocity in aggregates of (predominantly) hcp grains is investigated using theoretical, numerical and experimental methods. A representative volume element methodology is presented, enabling the effects of texture on ultrasonic wave speed to be investigated in two-phase polycrystals, and is employed to examine the ultrasonic response of random polycrystals, textured polycrystals and macro-zones often observed in titanium alloys. Numerical results show that ultrasonic wave speed varies progressively with changing texture, over a range of ∼200 m s−1, within bounds set by the two extreme single-crystal orientations. Experimental ultrasound studies and full electron backscatter diffraction (EBSD) characterization are conducted on unidirectionally rolled and cross-rolled Ti–6Al–4V samples in three orthogonal directions. In addition, the EBSD-determined textures are incorporated within the polycrystal model and predicted ultrasonic velocities compared directly with ultrasonic experiments. Good quantitative agreement is obtained and both the experimental and computed results demonstrate that ultrasonic velocity profiles exist for random, unidirectionally rolled and cross-rolled textures. The combined results indicate the possibility of the development of a methodology for bulk texture determination within Ti polycrystal components using ultrasound.

Journal article

Lan B, Feng PF, Wu ZJ, Yu DWet al., 2012, Determination of Constitutive Equation Parameters for Orthogonal Cutting through Pressure Bar Tests and FEA Method, Key Engineering Materials, Vol: 499, Pages: 56-61

<jats:p>This paper proposes a method of determining the constitutive equation parameters of a Japanese type of alloy steel (SCM440H) for Finite Element Analysis (FEA) of orthogonal cutting, involving pressure bar experiments, orthogonal metal cutting experiments and FEA inverse identification. First, Split Hopkinson Pressure Bar (SHPB) experiments combined with Quasi-Static pressure tests were conducted, and after analyzing and processing the experimental data, one set of original constitutive constants was obtained; in the mean time, orthogonal cutting experiments were also performed to collect the cutting force data. Then the original constants were put into FEA software to simulate the cutting process. But comparison between the orthogonal cutting experimental and the simulation results revealed the inadequacy for the constants to predict cutting forces. To address this problem, an inverse identification method was employed to optimize the constants iteratively. And after a certain number of iterations, the ideal parameters for FEA of the orthogonal cutting process were finally determined.</jats:p>

Journal article

Lan B, Feng PF, Wu ZJ, 2011, Identification of Material Constitutive Parameters Using Orthogonal Cutting Tests and Genetic Algorithm, Materials Science Forum, Vol: 697-698, Pages: 112-116

<jats:p>Identification of workpiece material constitutive parameters for their application in the simulation of metal cutting process has been a hot research spot for long. This paper proposes a methodology to address this problem using orthogonal cutting tests and Genetic Algorithm (GA). First, an analytical model which calculates the dynamic characteristics occurring in the primary shear zone is introduced; then, orthogonal cutting tests are carried out, to record the following mechanical characteristics with the analytical model: shear stresses, shear strains, strain rates, cutting temperatures; afterwards, GA is employed to obtain the constitutive parameters from these characteristics; at last, the finite element method (FEM) simulations of the cutting tests are performed to evaluate the predictive accuracies of the obtained parameters. In this paper, a Japanese brand steel SCM440H is used as the workpiece material, and the simulation results of its constitutive parameters show good agreements with the experimental data, which renders the feasibility of the proposed methodology.</jats:p>

Journal article

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