Investigations of Convective Drying of Thin and Thick Wet Materials

Creeping flame spread: Some new results and interpretation for material flammability characterization

The estimation of thermal sensation at the instant when a certain object is touched is becoming an important consideration in material evaluation. In a previous paper, we showed that the effective contact temperature of the object –when covered with a thin surface of a different material– could be implied from the thermal contact resistance of the nonsteady heat conduction between half infinite solids. However, when the thickness of the surface material of the contact object becomes the same depth as the thermoreceptor in the skin, the approximation by the thermal contact resistance no longer applies, and, therefore, deriving a strict analytical solution becomes difficult. We calculated the temperature distributions in the material for various material surfaces and the skin using a numerical method. We examined the influence on the effective contact temperature of the thickness and the heat properties of each surface material. As a result, deflection of effective contact temperature from the temperature of a material is determined by the temperature difference between the skin and the surface material/object, the heat properties of each, the thickness of the surface material, and the depth of thermoreceptor in the skin. This can be expressed by the relation of the nondimensional parameter function. When the thickness of surface material is thick enough, effective contact temperature is determined only by the heat property of the surface material, and it is unrelated to the thickness of the surface material and the thermal property of the object under it. The influences of the thickness of the surface material and the thermal property of the object on effective contact temperature appear when the thickness of surface material becomes very thin, and increases rapidly with a decrease in the thickness of the surface material. The criterion between thermally thick and/or thin material is quantitatively presented by the numerical simulation.

Accurate thickness measurement of thin layer material is usually difficult in ultrasonic nondestructive evaluation (NDE), because the reflected ultrasonic echoes often overlapped which makes it difficult to separate these echoes and get the arrival times accurately. This paper used improved space alternating generalized expectation maximization (SAGE) algorithm to separate the reflected echoes and estimate the echoes' parameters for the purpose of acquiring the accurate arrival time of the echoes. With the accurate arrival time estimated, the thin layer material's thickness can be evaluated. Two experiments were carried out on a thin steel sheet with 20 MHz and 5MHz transducers using the improved SAGE algorithm, and the results validate the method's accuracy.

This paper focuses on characterization of relative permittivity for thin slab artificial dielectric material using rectangular waveguide. The slab artificial dielectric material constructed of circular patch metallic copper on a rectangular shape of various thin materials is piled up in some configurations and densities. A rectangular waveguide with the dimension of 72.4mm × 34mm is employed as characterization tool. Variable of thin slab artificial dielectric material which will be investigated is thickness between 0.8mm to 8mm, composition using rhombic and orthorhombic, and number of unit cell. From characterization results, it is found that the increase of material thickness decreases its relative permittivity, whilst the orthorhombic composition has higher relative permittivity than the rhombic composition.

Non-destructive testing of material thickness which leaves materials undamaged is essential for many industries. In this article, we have developed a new simple method for thickness measurement of thin solid materials using E-shaped slots. In the proposed structure, two E-shaped slots are connected in a novel outline on top of a microstrip line. The current flow interruption leads to an inductive effect. Through additional charge accumulation at the slot corners, where electric fields concentrate, capacitance arises. The resonant frequency corresponding to inductance and capacitance of slots changes with the material thickness variation on top of the sensor due to distortion of the continuity of the field concentration of a microstrip line. The operation principle of the proposed sensor is based on the downshifting of the resonant frequency with respect to the material under test (MUT) thickness. The complete characterization of the proposed sensor with different MUT thicknesses including simulation results is provided. Electrical performance details of the whole structure are explained with a circuit model and parametric analysis. A prototype sensor is fabricated and successfully tested for different thin material thicknesses. The sensitivity analysis from measurement results shows 4.3% sensitivity, which is higher than most of the available sensors. The prototype sensor size is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15.63\times 15.63\times0.508$ </tex-math></inline-formula> mm3.

Force delivery properties of thermoplastic orthodontic materials

Thin multi-layered materials are widely used in key structures of many high technology industries. To ensure the quality and safety of structures, layer thickness measurement by non-destructive testing (NDT) techniques is essential. In this paper, a novel approach for the measurement of each layer’s thickness in thin multi-layered material is proposed by using ring-shaped laser generated focused ultrasonic bulk waves. The proposed method uses a ring-shaped laser with a variable radius to generate shear waves with variable focus inside the structure. By analyzing the signal characteristics at the ring center when the laser radius varies from zero to maximum, the direct measurement of layer thickness can be realized, considering that only when the focal depth and the layer thickness satisfy the specific relationship, the reflected shear waves converge and form a peak at the ring center. This straightforward approach can increase the pulse-echo SNR and prevent the processing of aliasing signals, and therefore provides higher efficiency and accuracy for the layer thickness measurement. In order to investigate the feasibility of this method, finite element simulations were conducted to simulate the ring-shaped laser generated ultrasonic waves in multi-layered structure in detail. Following the principle of the proposed method, the layer thickness of a bi-layer and 3-layer structure were respectively measured using simulation data. The results confirm that the proposed method can accurately and efficiently measure the layer thickness of thin multi-layered material.

Directional fluid motion driven by the surface property of solid substrate is highly desirable for manipulating microfluidic liquid and collecting water from humid air. Studies on such liquid motion have been confined to dense material surfaces such as flat panels and single filaments. Recently, directional fluid transport through the thickness of thin porous materials has been reported by several research groups. Their studies not only attract fundamental, experimental and theoretical interest but also open novel application opportunities. This review article summarizes research progress in directional fluid transport across thin porous materials. It focuses on the materials preparation, basic properties associated with directional fluid transport in thin porous media, and their application development. The porous substrates, type of transporting fluids, structure-property attributes, and possible directional fluid transport mechanism are discussed. A perspective for future development in this field is proposed.

We analyze the stress field near an interface edge of an elastic-creep bi-material with and without an additional constraint layer by finite element method. The focus is on the effect of material thickness on the stress field. The results reveal that the creep J-integral, J*, on a path in a creep zone near the interface edge, which characterizes the intensity of the singular stress field, time-dependently decreases and becomes constant in the large-scale creep condition. For thin creep materials, J* increases proportionally with an increase of the thickness, while it saturates when the thickness becomes about a quarter of the material width. The normalized creep J-integral by the creep material thickness is the general parameter of the stress intensity near the interface edge for the thin films. In unconstrained bi-material, the time to reach the steady state is independent of creep material thickness; however, the one in constrained bi-material increases as the thickness decreases.

The kinetics of convective drying of thin wet thermal insulation materials based on the relative drying rate and relative moisture contents has been studied. Processing of experimental data on drying of various wet materials has established that the relative drying rate is related to the relative moisture contents, which are the ratios of the current moisture content to its critical and initial values. Based on the functional dependence of the relative drying rate on the relative moisture contents using the processing of the experiment on drying of ceramics, felt, and asbestos, equations for calculating the drying time are obtained. The dependence of the relative drying rate on the ratio of the current moisture content to the critical one is given. Zonal methods for calculating the drying time are given, based on the drying rate curve. An expression for determining the drying coefficient is developed. Based on the analysis of experimental data on drying porous ceramics, sheet asbestos, and wool felt, graphs of the dependence of the relative drying rate on the ratio of the current moisture content to the initial one are constructed. Dependencies for determining the critical moisture content of the material are given. The considered method of processing experimental data allows obtaining all the main equations for calculating the kinetics of the drying process. A variant of estimating the drying time based on one experiment with a short time interval is given. A comparison of the calculated values according to the equations with the experiment is performed. The spread of the calculated values is in the range of experimental error. The formulas for calculating the drying time obtained without plotting the drying rate curve allow significantly reducing the time of processing the experimental data and can be applied to other materials.

A schlieren study of the generation of different types of ultrasonic waves in thin plates

A sudden increase in the usage of automotive vehicles results in sudden increases in the fuel consumption which results in an increase in air pollution. To cope up with this challenge federal government is implying the stricter environmental regulation to decrease air pollution. To save from the environmental regulation penalty vehicle industry is researching innovation which would reduce vehicle weight and decrease the fuel consumption. Thus, the innovation related to light-weighting is not only an option anymore but became a mandatory necessity to decrease fuel consumption. To achieve this target, the industry has been looking at fabricating components from high strength to ultra-high strength steels or lightweight materials. With the usage of advanced high strength steels, the lightweight was achieved by reducing a gage thickness without compromising the strength aspect. However due to their high strength property often challenges occurred are higher machine tonnage requirement, sudden fracture, geometric defect, etc. The geometric defect comes from the elastic recovery of a material, which is also known as a springback. Springback is commonly known as a manufacturing defect due to the geometric error in the part, which would not be able to fit in the assembly without secondary operation or compensation in the forming process. It is learned that the springback of the material increases with an increase in the material strength and/or decrease in material thickness. In advanced high strength steels, higher strength and lower gage thickness options make the part prone to higher springback. Due to these many challenges with the materials and their properties which affect the springback, other research routes involved are innovative forming processes which would reduce the springback such as applying electricity through the material after forming and before the release of the load, performing warm or hot forming, die compensation, etc. One such innovative and patented process which is studied in the paper is using rollers in the tool i.e., in die and punch during the forming process. In this paper, the 2D channel strip of the aluminum 2024 high strength and thin material will be used in the bending processes. The process will be simulated in ABAQUS finite element software. First, the conventional channel bending process will be performed and springback will be analyzed as compared to the desired shape. Then the tool rollers will be implied to the die and punch corner radius and then the channel bending process will be performed and springback will be analyzed. The roller rotations will be set constant in this study, but the motion i.e., clockwise or counterclockwise in both die and punch will be studied on the springback of the channel. In addition, the no rotation of the roller effect on the springback will be studied and results will be compared. Further the maximum stress before and after springback and the stress distribution all cases will be analyzed and presented.

In order to increase the performance and efficiency of current tactile sensors, the study on the versatility of the human hand and tactile function could provide excellent hint. Our objective is to develop a new algorithm based on comparing the behavior of human tactile mechanism (using psychophysics experiment) vs. a robotic hand (equipped with 3-axis tactile sensor) using stainless steel (SUS) foils and 1,000-yen bills as medium. The significance of tangential load is highlighted to distinguish between material thicknesses. The result from the first experiment shows that using normal vs. angled load, the Weber fraction is high during low thickness and decreased with increase of thickness. In the second experiment, we find that the ability to distinguish between sheet numbers improves by increasing tangential load compared to just normal load. Overall, it is noted that the tangential load makes the tactile sensor distinguish extremely thin material.

This is the first paper in a two-part sequence that evaluates the microwave dielectric behavior of vegetation material as a function of water content, microwave frequency, and temperature. Part I presents experimental measurements of the dielectric spectrum from 0.2 to 20 GHz for various types of vegetation material including leaves, stalks, and trunks at various moisture conditions. The measurements were acquired using a coaxial probe technique suitable for measuring the dielectric constant of both thick materials, such as tree trunks, and thin materials, such as leaves. In Part II, the experimental data are used to guide the development of a dual-dispersion dielectric model that incorporates the dielectric properties of water in both "free" and "bound" forms.

Tearing resistance of some co-polyester sheets