Non-uniform Microstructure Research Articles

Thermomechanical Simulation of Ferritic Rolling of Titanium-Niobium Interstitial-Free Steel

Abstract Austenitic or two-phase rolling of ultra-low carbon steels face temperature control issues and generate shape defects. Ferritic rolling has been developed as a solution, and ferritic hot-rolled sheets are used as final products, replacing hot-rolled followed by cold-rolled sheets. However, it is not in regular industrial production because of mill limitations. Hence, ferritic hot rolling must be optimized for developing a ferritic cold-rolled and close-annealed sheet through subsequent processing. In this work, industrial ferritic rolling process was simulated for a titanium-niobium interstitial-free steel using a thermomechanical simulator. Multi-hit plane strain compression tests were carried out at three different regimes below the lower transformation temperature (Ar1). Steels were processed under high strain and strain rates as experienced during industrial hot rolling operation, and the results were compared with the conventional austenitic rolling. The flow stress of the material in the ferritic regime decreased with decreasing deformation temperatures but increased at temperatures below 700°C. Nonuniformity in grains and texture also increased with decreasing temperatures. High-temperature rolling in ferritic condition close to Ar1 temperature does not differ significantly from the austenitic condition, whereas the low-temperature ferritic rolled material had through-thickness microstructural nonuniformity and unwanted goss and brass fibers. The intensity of gamma-fiber {111} || normal direction (ND) required for formability was highest in the intermediate temperature zone. Deformation between temperatures of 850°C and 800°C was found to be ideal. Based on simulation studies, full-scale plant rolling was carried out under the optimized ferritic regime. The microstructure and texture matched closely with the simulation results. This work provides a working window for ferrite rolling in an industrial hot strip mill for developing ferritic cold-rolled close-annealed products.

Surface, microstructure, and tensile deformation characterization of LPBF SS316L microstruts micromachined with femtosecond laser

Considerable surface roughness, dimensional deviation, and non-uniform microstructure are a few of the characteristics found on thin or micro-scale features fabricated via laser powder bed fusion (LPBF) that yield inferior and/or inconsistent mechanical properties. Femtosecond laser micromachining can aid in fabricating micro-scale parts with ultra-high dimensional precision. In this work, the surface and tensile behavior of microstruts of 500μm nominal diameter micromachined with Gaussian laser pulses of <100fs duration are characterized. Roughness parameters such as Ra=0.9±0.2μm and Rz=3.4±1.3μm are achieved on the micromachined faces. Surface-associated grains are successfully ablated with negligible microstructural damage to the microstruts. As a result, the average uniform strain under quasi-static tensile loading is measured as 0.54±0.02 compared to 0.42±0.01 for the as-built microstruts. Uniform and non-uniform deformation strain portions are separated analytically and characterized primarily via in-situ imaging. Progressive degradation of the surface and dimensional variance is observed on the micromachined test specimens. Post necking initiation, ablation-associated asperities on the micromachined surfaces evolve into notches, leading to tensile failure.

Mesoscale Process Modeling of a Thick Pultruded Composite with Variability in Fiber Volume Fraction.

Pultruded fiber-reinforced polymer composites are susceptible to microstructural nonuniformity such as variability in fiber volume fraction (), which can have a profound effect on process-induced residual stress. Until now, this effect of non-uniform distribution has been hardly addressed in the process models. In the present study, we characterized the distribution and accompanying nonuniformity in a unidirectional fiber-reinforced pultruded profile using optical light microscopy. The identified nonuniformity in was subsequently implemented in a mesoscale thermal–chemical–mechanical process model, developed explicitly for the pultrusion process. In our process model, the constitutive material behavior was defined locally with respect to the corresponding fiber volume fraction value in different-sized representative volume elements. The effect of nonuniformity on the temperature and cure degree evolution, and residual stress was analyzed in depth. The results show that the nonuniformity in fiber volume fraction across the cross-section increased the absolute magnitude of the predicted residual stress, leading to a more scattered residual stress distribution. The observed gradient promotes tensile residual stress at the core and compressive residual stress at the outer regions. Consequently, it is concluded that it is essential to take the effects of nonuniformity in fiber distribution into account for residual stress estimations, and the proposed numerical framework was found to be an efficient tool to study this aspect.

A three-dimensional multiscale approach to optimal design of porous structures using adaptive geometric components

This paper presents a direct multiscale design approach for three-dimensional (3D) porous structures. The porous material modeling technique, which involves the use of the adaptive geometric components (AGCs), is employed to simultaneously describe the macrostructure and microstructure of material while the multiresolution topology optimization (MTO) is utilized to reduce the cost of finite element analysis (FEA). We use two distinct discretization levels, including a coarse mesh to perform FEA (displacement mesh) and a fine mesh to present material distribution (density mesh). The AGCs are smoothly mapped onto the density mesh to obtain an effective element density field for material interpolation and stiffness computation of displacement-mesh elements. The overall macrostructure and microstructure of the material are simultaneously optimized by straightforwardly optimizing the geometry parameters of the AGCs. The 3D porous multiscale design with non-uniform microstructure can be directly achieved with only a global volume constraint. Some numerical tests are provided to validate the applicability of the proposed approach.

THE DEFORMATION OF AZ31 MAGNESIUM ALLOY DURING WARM CONSTRAINED GROOVE PRESSING

A magnesium alloy AZ31 as plate of dimensions (60 x 60 x 3) mm has been constrained groove pressed (CGP) four deformation passes (16 pressings) at 250 oC by simulation and experiments. On the basis of the analysis of calculation results about the deformation distribution in the alloy AZ31 workpieces, the mechanism for its microstructure evolution during the severe plastic deformation (SPD) process was partly clarified. On the other hand, deformation heterogeneity distribution developed in the workpieces by applying CGP caused the evolution of a non-uniform microstructure. The TEM microstructure analysis results provided clear evidence that across the plate both the banded deformed microstructure where dislocation cell structure and/or partially or fully recovered polygonized subgrain microstructure are present. The recovering dynamic and local polygonization process contributes significantly to the formation of ultra-fine materials (UFG) microstructure.

Implication of Non-Uniform Anode Particle Morphology on Lithium-Ion Cell Performance

The present works deals with the implications of non-uniform anode particle morphology on charging and discharging characteristics of Lithium-ion cell, especially for ultra-fast charging applications. The one-dimensional isothermal model is employed to analyze the effect of C-rate, porosity, tortuosity, and particle geometry for a range of non-uniform anode particle size distribution numerically. Our study reports that the value of capacity and specific power of the cell is found to be maximum when the particle size decreases along the electrode length. In contrast, capacity and specific power are minimum when anode particle size increase along the anode length. Moreover, a significant improvement in the performance of the Lithium-ion battery is found at ultra-fast charging when non-uniform particle distribution is employed. Additionally, a strong interplay of particle distribution and microstructural attributes viz. porosity and tortuosity on cell performance are revealed for the charging-discharging cycle. Further, the capacity of the cell is found to be maximum when the particle geometry is spherical. We anticipate that the results can inspire further improvement in ionic transport for ultrafast charging with non-uniform microstructure in the Li-ion cell.

Fatigue strength distribution and probabilistic evaluation on stainless steel welded components under mixed mode loading

Plane sheet specimens and their welded components were examined through fatigue tests, and the data were evaluated by the base line regression model. The three-parameter Weibull estimations showed the most accurate approximation of the measured values with the median rank treatment. The fatigue strengths, limits, lives and failure probabilities under different loading conditions became predictable. The fatigue strengths and limits under mixed mode loading were compared with the Gough–Pollard relation, and could be predicted from the load ratio of the torsion to bending. The notch factors of welded components were 1.24–2.55 at the load ratio of 0.31. The fatigue strengths and scatters mainly depended on the weld flank angle, and had excellent agreement with the weld shape parameter which included the influence of the weld toe radius. They varied with the material factor which included the influences of the non-uniform microstructure, weld imperfection, etc.

Eutectic growth mechanism and heat transfer dynamics of ternary Cr-Ni-Fe alloy during triple containerless processing

The rapid solidification of ternary Cr49.5Ni40.5Fe10 alloy was realized by triple containerless processing techniques including free fall, falling quench and direct quench in order to systematically investigate its eutectic growth mechanism under different heat transfer conditions. Based upon Newtonian cooling model and classical heat transfer equation, the thermal information inside alloy droplets was obtained to derive the cooling rate, temperature difference and temperature gradient. After containerless solidification, the macroscopic segregation of primary δ phase was remarkably reduced owing to the microgravity effect and the spherically symmetrical temperature field within alloy droplets. Three typical eutectic structures were observed in the alloy droplets. With the increases of cooling rate, temperature difference and temperature gradient, the microstructures of alloy droplets evolved from coarse lamellar eutectic to refined anomalous eutectic and finally transformed to coarse anomalous eutectic because of the independent growth of δ and γ phases. Especially, under falling quench condition, a non-uniform eutectic microstructure appeared, which was refined gradually from the surface to the center of alloy droplets. This was attributed to the sudden changes of these three thermodynamic parameters once the alloy droplets were rapidly quenched into liquid coolant.

Parametrically homogenized continuum damage mechanics (PHCDM) models for unidirectional composites with nonuniform microstructural distributions

This paper develops a parametrically homogenized continuum damage mechanics (PHCDM) model for multiscale analysis of damage and failure in composite structures with nonuniform microstructures. Unidirectional glass fibers are nonuniformly dispersed in the microstructures of these epoxy matrix composites. The PHCDM models are thermodynamically consistent, reduced order constitutive models with coefficients that are explicit functions of microstructural descriptors and evolving material variables. Damage anisotropy is represented through a second order damage tensor that contributes to the evolution of a damage surface in the space of damage work conjugate, which characterizes the initiation and evolution of damage. The nonuniform microstructural morphology descriptors are optimally expressed in terms of representative aggregated microstructural parameters or RAMPs for incorporation in the PHCDM coefficients. Optimal expressions for RAMPs are determined through principal component analysis of the two-point correlation functions. The functional forms of RAMPs in PHCDM coefficients are determined using machine learning tools operating on data generated by micromechanical analysis. It is shown that PHCDM models accounting for the fiber distribution information yield a much higher accuracy than those only accounting for fiber volume fractions. The developed PHCDM model is incorporated in a commercial finite element code and structural analysis of structural composites is executed for understanding concurrent damage and failure at multiple scales. The paper successfully demonstrates the accuracy and significant efficiency of the resulting PHCDM model in analyzing deformation and damage in nonuniform composites across length scales for various loading conditions.

Improved Wear and Corrosion Resistance of Microarc Oxidation Coatings on Ti–6Al–4V Alloy with Ultrasonic Assistance for Potential Biomedical Applications

Although microarc oxidation is frequently used in producing wear‐ and corrosion‐resistant coatings on Ti and Ti alloys for biomedical applications, the formation of nonuniform microstructure of the coatings is still unavoidable. To overcome this drawback, this work adopts ultrasonic assistance in the microarc oxidation of Ti–6Al–4V and systematically investigates the influences of ultrasonic treatment with different durations on the coating microstructures and resultant properties. The positive effects of ultrasonic, such as cavitation effect, sound flow effect, and mechanical effect, accelerate the cooling rate of electrolyte and promote the homogeneity of the solute on the sample surface. Therefore, the ultrasonic‐assisted coatings exhibit uniform microstructures with fewer cracks and therefore improve performances. For instance, compared with the counterpart without ultrasonic assistance, the ultrasonic‐assisted coating with 15 min duration demonstrates 25.1% lower mass loss in the tribology test and half corrosion density in Hank's solution. Such results indicate that ultrasonic assistance in microarc oxidation of Ti–6Al–4V can homogenize the microstructures of coatings and enhance their corrosion resistance and wear resistance in human body.

Computational homogenization of fully coupled multiphase flow in deformable porous media

In this paper, a computational modeling tool is developed for fully coupled multiphase flow in deformable heterogeneous porous medium that consists of complex and non-uniform micro-structures using the dual continuum scales based on the computational homogenization approach. The first-order homogenization technique is employed to perform the multi-scale analysis. The governing equations of two-phase flow of immiscible fluids, including an equilibrium equation and two mass continuity equations, are considered based on the appropriate main variables. According to the well-known Hill–Mandel principle of macro-homogeneity, the proper energy types are defined instead of conventional stress power for linking micro- and macro-scales, which plays a significant role in determination of consistent microscopic fields. The finite element squared strategy is utilized to resolve the two scales simultaneously. The periodic and linear boundary conditions are exploited in the micro-scale analysis, and the macroscopic quantities such as stress tensor, inertial force vector, flux vectors and fluid contents are determined from the boundary information of microscopic domain. Moreover, a general approach is defined depending on the type of boundary condition in which the macroscopic tangent operators can be extracted directly from the converged microscopic Jacobian matrix. Finally, in order to illustrate the efficiency and accuracy of the proposed computational algorithm, several numerical examples are solved, and the effects of various parameters, such as boundary conditions, RVE types, RVE length scale, and volume fraction of heterogeneities are investigated.

Effect of Substrate Plate Heating on the Microstructure and Properties of Selective Laser Melted Al-20Si-5Fe-3Cu-1Mg Alloy.

The Al-20Si-5Fe-3Cu-1Mg alloy was fabricated using selective laser melting (SLM). The microstructure and properties of the as-prepared SLM, post-treated SLM, and SLM with substrate plate heating are studied. The as-prepared SLM sample shows a non-uniform microstructure with four different phases: fcc-αAl, eutectic Al-Si, Al2MgSi, and δ-Al4FeSi2. With thermal treatment, the phases become coarser and the δ-Al4FeSi2 phase transforms partially to β-Al5FeSi. The sample produced with SLM substrate plate heating shows a relatively uniform microstructure without a distinct difference between hatch overlaps and track cores. Room temperature compression test results show that an as-prepared SLM sample reaches a maximum strength (862 MPa) compared to the heat-treated (524 MPa) and substrate plate heated samples (474 MPa) due to the presence of fine microstructure and the internal stresses. The reduction in strength of the sample produced with substrate plate heating is due to the coarsening of the microstructure, but the plastic deformation shows an improvement (20%). The present observations suggest that substrate plate heating can be effectively employed not only to minimize the internal stresses (by impacting the cooling rate of the process) but can also be used to modulate the mechanical properties in a controlled fashion.

Failure and metallurgical defects analysis of IN-738LC gas turbine blades

Catastrophic and early failure of third stage blades of a gas turbine was investigated. Some areas on the fracture surface of 4 blades were covered with thick black oxide layer. Quantitative microscopic measurements of primary γ′ and MC carbide phases showed that the blades were not exposed to excessive temperature. Scanning electron microscopy and energy dispersive spectroscopy analysis of oxide layer on fracture surface and stress ruptured specimens within 760–980 °C up to 100 h, and heat-treated specimens were used to calculate the blades temperature. The results revealed that oxide bifilms discontinuities and internal cracks accompanied with shrinkage cavities, nucleation and dendritic growth of γ′ precipitates, and non-uniform microstructure led to locally weakened structures at the bottom of airfoils. Accordingly, uncontrolled parameters in casting were the main reasons for commencing the failure.

Investigation on microstructure and properties of dissimilar joint between TRIP800 and QP980 fabricated by laser welding

Dissimilar weld joints of QP980 and TRIP800 were fabricated by a fibre laser. The microstructure and mechanical properties of dissimilar weld joints were studied. The tensile properties of weld joints were not influenced by the narrow softening zone with a less reduction in hardness of ∼25 HV from the QP980, which contributed to fracture in TRIP800. The DIC images showed that the location of maximum strain was changed from the QP980 side to TRIP800 side during the tensile test of QP980 (1.2 mm)–TRIP800 (1.4 mm) joints. The dissimilar weld joints were characterised by the limited dome height test (LDH). The LDH values were varied with the punch pole location, as a result of the softening zone and non-uniform microstructure on the heat-affected zone of joints.

Microstructure Distribution Parameters for Ferrite-Martensite Dual-Phase Steel

The microstructure was observed and measured on the two kinds of commercially pure sheet iron and DP600 steel so as to reveal its distribution nonuniformity. The distribution of two grain parameters viz the grain size d and grain shape coefficient λ were analyzed on the measurement interval of 0.1, 0.05, and 0.01 μm. Both d- and λ -distributions are nonuniform. These parameters are similarly distributed and consistent with the Gaussian distribution. The nonuniform d- and λ-distributions can be described precisely on a sufficiently large specimen and a reasonable interval length. The nonuniformity of microstructure and materials can be accurately described by constructing the models of dislocation, deformation, and strain-hardening nonuniformity.

Influence of Microstructure on Initial Corrosion Behavior of Steel Materials Using Kelvin Force Microscope

Improvement of the efficiency of power engines and reduction of the vehicles weight are important to boost the fuel efficiency of transportation equipment such as automobiles. One of the countermeasures is to expand the application of ultra-high tensile steel materials to structural members. However, the surface of ultra-high tensile steel becomes often non-uniform due to the metallographic control during manufacturing. Surface non-uniformities are more likely to lead to corrosion. Therefore, in order to further expand the application of ultra-high tensile steel materials, it is necessary to fully understand local corrosion behavior such as selective corrosion depending on the metal structure and grain boundaries. The purpose of this study is to research an influence of the non-uniformity of surface microstructure on corrosion of steel material, and the surface potential of each metallographic structures was measured by the Kelvin force microscope (KFM).Carbon steel (S45C) was heat-treated under conditions of holding it at 1250°C for 30 minutes and cooling in the furnace. After the sample surface was mirror-polished, the sample surface was smoothed by performing ion milling as a pretreatment for the KFM measurement. The KFM measurement was conducted for a predetermined range with 0.30 Hz of a scanning frequency, and the surface shape image was also measured in AFM mode. Furthermore, a corrosion test was conducted by immersion in a borate buffer containing 0.01 mol dm-3 NaCl for 1 hour, in order to clarify the relationship between the surface potential distribution obtained by KFM measurement and the initial corrosion behavior. After that, the sample surface was thoroughly washed with distilled water, dried, and KFM measurement was performed again.The surface morphology and the potential of the samples before the corrosion test changed periodically corresponding to the ferrite and cementite phases in pearlite. The potential of the cementite phase was about 10 mV lower than that of the ferrite phase. It was suggested that the interface between the cementite phase and the ferrite phase becomes an origin of corrosion, since the place showing the large potential difference is likely to be the starting point of corrosion. In comparing the surface morphology of the samples before and after the corrosion test, the width of the cementite phase was clearly narrower than that before the corrosion test. The surface potential of this part of the sample before the corrosion test showed more negative potential than the surroundings, which is considered that the shape change is attributed to the dissolution of the metal. Therefore, it was concluded that the potential distribution of the sample before the corrosion test is closely related to the corrosion behavior.

Exploring Component Interactions during Mechanical Degradation of Fuel Cell Membranes with 4D in Situ Visualization

The ionomer membrane facilitates critical functions in a polymer electrolyte membrane fuel cell. Dynamic operational duty cycles can gradually introduce various damage features within the membrane, which could lead to overall performance failure of the fuel cell. Membrane durability is affected by chemical, mechanical, and thermal stressors that often act synergistically to degrade the ionomer membrane during fuel cell operation [1]. However, to understand the effect of each individual stressor, a useful approach is to isolate and study these degradation mechanisms separately. For instance, pure mechanical membrane degradation is typically affected in situ by actively cycling the membrane hydration levels under electrochemically inert conditions. These conditions generate cyclic mechanical stresses within the constrained membrane, leading to fatigue-induced fracture and electrode delamination under prolonged exposures [2]. When the cracks penetrate completely through the membrane thickness and spread across a substantial planar area, internal gas crossover is accelerated through convective transport, and ultimate fuel cell failure could result [3]. Furthermore, the mechanical membrane damage is strongly influenced by the microstructure of the adjoining membrane electrode assembly (MEA) components and cell design. Failure analysis investigations, using both 2D and 3D imaging, have consistently found significant proportion of membrane cracks to be co-located with the electrode cracks, which is typically attributed to the local stress concentration effects that could favour membrane crack initiation at these sites [2,4–6]. Recently, X-ray computed tomography (XCT) based 4D in situ visualization approach adopting a custom X-ray transparent fuel cell assembly [7] provided further insights into such interaction effects by demonstrating the temporal development of new membrane cracks underneath pre-existing electrode features [8].Given the dominant role of electrode cracks in membrane fracture, the present work was undertaken to explore low crack density electrodes as a mitigation strategy against mechanical membrane degradation. This was achieved by subjecting two separate MEAs with different initial cathode catalyst layer (CCL) crack densities, i.e., high and low crack designs, to accelerated stress test (AST) involving humidity cycling for generating pure mechanical degradation. Periodic XCT-based in situ visualization was performed to elucidate differences in the magnitude and evolutionary processes of the membrane/MEA degradation between the two examined cases. Failure mechanisms responsible for mechanical membrane fracture were investigated in relation to the role of neighbouring components ― both electrodes and gas diffusion layers (GDLs).Membrane damage was found to be significantly curtailed through minimization of ab initio crack density in the CCL. While through-thickness membrane cracks developed within a similar timeframe in both high and low cathode crack density MEAs, the coverage area of fatigue-induced membrane fracture in the latter case was nearly six times lower after 2000 AST cycles, thereby establishing the adopted treatment of electrode morphology as an effective mitigation strategy in slowing the mechanical membrane degradation rate. Hydration-dehydration cycles, however, still altered this initial morphology by introducing electrode cracks at early stages of the AST. These electrode cracks, as an intermediate step, exclusively governed the subsequent initiation and propagation of membrane cracks. Two distinct membrane failure mechanisms were identified, each characterized by the presence and absence, respectively, of the MEA’s permanent buckling deformation into void spaces of the GDL (Figure 1). The buckling phenomenon was found to be strongly influenced by the non-uniform GDL microstructure and had a significant contribution towards the eventual frequency and coverage of membrane fracture. This finding suggests that critical component interactions during membrane failure extend beyond the immediately adjacent electrode layers. Additional comparative in situ visualizations of the fuel cell assembly held at varying hydration states showed that the size and geometry of the membrane fracture features that had developed in the low cathode crack MEA varied substantially between dry and wet environments. Acknowledgements Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and Ballard Power Systems through an Automotive Partnership Canada grant. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

Constructing Gradient Porous Structure in Thick Li4Ti5O12 Electrode for High-Energy and Stable Lithium-Ion Batteries

The manufacturing process for electrodes in lithium-ion batteries generally results in a nonuniform microstructure geometrically distributed in the through-thickness direction of an electrode. A po...

Influence of a Nonuniform Microstructure on the Rolling Contact Fatigue Properties of ER8 Steel Wheel

To mitigate the damage caused by rolling contact fatigue (RCF) on wheels, RCF tests are conducted to obtain the RCF limit of the surface area of an ER8 wheel tread that comprised a nonuniform microstructure. The microstructure topography of the RCF area is observed with optical microscopy, a scanning electron microscopy, and a transmission electron microscopy. The hardness, elasticity, and plasticity of different areas of the nonuniform microstructure are analyzed with a nanoindentation instrument. The results show that, besides pearlite and proeutectoid ferrite (matrix), a large amount of upper bainite is present. This component, therefore, interrupts the continuity of the wheel steel matrix, leading to a nonuniform microstructure and an RCF limit of 1074 MPa, which is lower than that of a wheel worn to the limit area and that comprised a normal microstructure. Furthermore, cracks mainly initiate and propagate at the boundary of the upper bainite and matrix. Although the hardness and the elasticity of the upper bainite are higher than those of the matrix, the plasticity is lower. Furthermore, under the effect of the contact stress, the difference between their deformations leads to stress concentration at the boundary, facilitating the initiation and propagation of cracks in steel wheels and accelerating the damage due to RCF.

Mass transfer and texture characteristics of fish skin during deep-fat frying, electrostatic frying, air frying and vacuum frying

Fried fish skins are snacks with rich flavor in Asian. However, the high fat content about 50% is not good for health. It is possible to reduce the oil content while maintain its fried taste and texture by optimized frying methods. The effects of different frying approaches such as air frying, vacuum frying, electrostatic frying and traditional deep-fat frying on the oil uptake, moisture loss, breaking force, color, and microstructure attributes of fried fish skins were studied. Air and oil frying were performed at 180 °C for 2–12 min. Vacuum frying was conducted at lower temperature 120 °C for 4–24 min. Results showed that air fried and vacuum fried fish skins had the lowest fat contents (9.8% and 27.7%, respectively) and showed smooth, uniform microstructures. On the contrary, holy, irregular and non-uniform microstructures were obtained by traditional deep-fat frying and electrostatic frying due to high heat and rapid mass transfer occurred. The oil uptake (47.6% and 46.3% fat content, respectively) and browning reactions were also significant. Air frying developed a slower water evaporation rate and higher fish skin puffing ratio, which was suggested to be an alternative to traditional deep-fat frying.