The Effects of Core Machining Configurations on the Mechanical Properties of Cores and Sandwich Structures

Composite sandwich structures are widely used in the fields of aviation, marine, and energy due to their high specific stiffness and design flexibility. Improving the mechanical properties of the cores is significant to the strength, modulus, and stability of composite sandwich structures. Two kinds of core machining configurations were designed by combining thin grooves, perforated holes, and thick contour cuts as well as non-machining plain cores. The cores and sandwich structures with these configurations were fabricated using a vacuum-assistant infusion process. Static tensile, compressive, shear, and peeling tests were conducted on the infused cores and sandwich structures. The results showed that the tensile, compressive, and shear moduli, and compressive strength of the infused cores can be greatly improved. The tensile strength changed negligibly due to stress concentration induced by irregular foam cell and the shear-lag phenomenon of the resin column/foam interface. The shear strength of the infused cores increased slightly. The thick contour cuts and perforated holes can greatly improve the face sheet/core peel capacity of the sandwich structures, whereas the thin grooves can moderately improve the peel capacity. Both infused cores with the designed machining configurations exhibited positive effects on the compressive, tensile, and shear moduli, and compressive strength, considering the material costs. The study provides a comprehensive and quantitative insight into the effects of core machining configurations on mechanical properties of infused cores and composite sandwich structures.

The Effect of Batter Characteristics on Protein-Aided Control of Fat Absorption in Deep-Fried Breaded Fish Nuggets

Soy protein (SP), egg white protein (EP), and whey protein (WP) at 6% w/w were individually incorporated into the batter of a wheat starch (WS) and wheat gluten (WG) blend (11:1 w/w ratio). Moisture adsorption isotherms of WS and proteins and the viscosity, rheological behavior, and calorimetric properties of the batters were measured. Batter-breaded fish nuggets (BBFNs) were fried at 170 °C for 40 s followed by 190 °C for 30 s, and pick-up of BBFNs, thermogravimetric properties of crust, and fat absorption were determined. The moisture absorption capacity was the greatest for WS, followed by WG, SP, EP, and WP. The addition of SP significantly increased the viscosity and shear moduli (G″, G′) of batter and pick-up of BBFNs, while EP and WP exerted the opposite effect (p < 0.05). SP, EP, and WP raised WS gelatinization and protein denaturation temperatures and crust thermogravimetry temperature, but decreased enthalpy change (ΔH) and oily characteristics of fried BBFNs. These results indicate that hydrophilicity and hydration activity of the added proteins and their interactions with batter matrix starch and gluten reinforced the batter and the thermal stability of crust, thereby inhibiting fat absorption of the BBFNs during deep-fat frying.

Effects of temperature and thermal cycles on the mechanical properties of expanded polystyrene foam

Understanding the effects of high temperature and thermal cycles on the mechanical properties of expanded polystyrene (EPS) foam is critical for its use in sandwich panels. This paper presents an experimental investigation of these effects in typical environmental conditions that exist in construction applications. A total of 117 small specimens were cut from metal-faced sandwich panels with EPS core and were exposed to different numbers of thermal cycles and/or sustained high temperatures. The specimens were then loaded under compression, tension, and four-point bending for evaluating the degradation of the mechanical properties of the foam. The thermal cycles reflect typical surface temperature during daily summer conditions, with a period of 24 h each and with a temperature varying between 24°C to 80°C. The results show that the modulus of elasticity of EPS foam in compression reduced by about 38% after exposure to thermal cycles for 45 days, whereas the tensile and shear moduli reduced by about 5.7% and 13.8%, respectively. Exposure to sustained high temperature after thermal cycles led to larger degradation of the elastic and shear moduli in the range of 38%–50%. These degradations can lead to early failures in applications that rely on the EPS foam as a structural component like in insulating sandwich panels.

A Comparison of Experimental and Computation Results of Finding Effective Characteristics of Elastic Properties of Polymer Layered Composites from Carbon and Glass Fabrics

Anisotropy of mechanical properties of the entire material and each of its layers is characteristic for polymer layered composite materials, as well as the fact that production processes of the composite material and parts from it are often combined in time. In this case, the elastic properties and strength of the material will be different not only in the thickness of the part, but also at each point. All this leads to a complication of the design process, which is due to the need to determine the elastic properties and strength of the polymer layered composite materials, taking into account the structure of the entire material and each of its layers. This work aims at evaluating the existing computational methods of finding effective characteristics of elastic properties by comparing computation results obtained by various methods with each other, as well as with the experimental results related to elastic properties of polymer layered composite materials from carbon and glass fabrics. We estimated the computational methods of finding effective characteristics of the elastic properties of composites based on the experimental results of finding the characteristics of the elastic properties of polymer layered composite materials made of carbon and glass fabrics, differing in density and type of weaving. The experimental values of the effective characteristics of elastic properties were determined as a result of standard tensile tests of laboratory specimens. As a result of the study, it was found that all the considered models and methods give consistent results when calculating the longitudinal modulus of elasticity E 11, the results of calculating shear modulus E 33 and shear moduli G 12 and G 23 are less consistent for all the considered materials. The comparison of the results of the experimental studies and computations showed that the Chamis model and the bridge model are better than other models to predict the values of the longitudinal elastic modulus.

Biot's equations-based reservoir parameter inversion using deep neural networks

Reservoir parameter inversion from seismic data is an important issue in rock physics. The traditional optimisation-based inversion method requires high computational expense, and the process exhibits subjectivity due to the nonuniqueness of generated solutions. This study proposes a deep neural network (DNN)-based approach as a new means to analyse the sensitivity of seismic attributes to basic rock-physics parameters and then realise fast parameter inversion. First, synthetic data of inputs (reservoir properties) and outputs (seismic attributes) are generated using Biot's equations. Then, a forward DNN model is trained to carry out a sensitivity analysis. One can in turn investigate the influence of each rock-physics parameter on the seismic attributes calculated by Biot's equations, and the method can also be used to estimate and evaluate the accuracy of parameter inversion. Finally, DNNs are applied to parameter inversion. Different scenarios are designed to study the inversion accuracy of porosity, bulk and shear moduli of a rock matrix considering that the input quantities are different. It is found that the inversion of porosity is relatively easy and accurate, while more information is needed to make the inversion more accurate for bulk and shear moduli. From the presented results, the new approach makes it possible to realise accurate and pointwise inverse modelling with high efficiency for actual data interpretation and analysis.

Premelting and the Machanisms of Melting in the Alkali Halides

<p>An experimental and theoretical study of premelting behaviour and mechanisms of melting in the alkali-halides is presented. Theories of melting and previous premelting experiments are first reviewed, then an elastic strain theory of melting is developed, which includes dilatation and shear contributions to the elastic energy and to the vibrational entropy, as well as a communal entropy and an entropy due to the isothermal expansion on melting. By fitting experimental melting parameters, dislocation-like local strains are implicated. The bulk and shear moduli are shown to be continuous with respect to dilatation through the melting expansion and one of the shear moduli vanishes at the dilatation of the melt at the melting temperature. A modified Born instability theory of melting is thus valid. Premelting rises in the apparent specific heat and electrical conductivity within 6 K of the melting point are studied and are shown to occur at the surfaces only. The use of guard rings to eliminate surface conduction is essential at all temperatures above the extrinsic/intrinsic conductivity 'knee', and electrical fringing must be taken into account for typical specimen sizes. For various surface orientations, the rises in surface conductivity occur at lower temperatures the lower the surface packing density, and for deformed specimens, the greater the deformation. The results are interpreted in terms of an atomic-scale surface melting below the melting point, and a consequent rapid rise in vaporisation rate. A dislocation theory of surface melting, melting and the solid-liquid interface is developed which gives good agreement with experimental values for the melting temperatures and the interfacial energies.</p>

Premelting and the Machanisms of Melting in the Alkali Halides

<p>An experimental and theoretical study of premelting behaviour and mechanisms of melting in the alkali-halides is presented. Theories of melting and previous premelting experiments are first reviewed, then an elastic strain theory of melting is developed, which includes dilatation and shear contributions to the elastic energy and to the vibrational entropy, as well as a communal entropy and an entropy due to the isothermal expansion on melting. By fitting experimental melting parameters, dislocation-like local strains are implicated. The bulk and shear moduli are shown to be continuous with respect to dilatation through the melting expansion and one of the shear moduli vanishes at the dilatation of the melt at the melting temperature. A modified Born instability theory of melting is thus valid. Premelting rises in the apparent specific heat and electrical conductivity within 6 K of the melting point are studied and are shown to occur at the surfaces only. The use of guard rings to eliminate surface conduction is essential at all temperatures above the extrinsic/intrinsic conductivity 'knee', and electrical fringing must be taken into account for typical specimen sizes. For various surface orientations, the rises in surface conductivity occur at lower temperatures the lower the surface packing density, and for deformed specimens, the greater the deformation. The results are interpreted in terms of an atomic-scale surface melting below the melting point, and a consequent rapid rise in vaporisation rate. A dislocation theory of surface melting, melting and the solid-liquid interface is developed which gives good agreement with experimental values for the melting temperatures and the interfacial energies.</p>

Comparative study of destructive, nondestructive, and numerical procedures for the determination of moisture dependent shear moduli in Scots pine wood

In this study, moisture dependent shear moduli in Scots pine (Pinus sylvestris L.) wood were determined by a 45° off-axis (longitudinal, radial, and tangential) compression test and ultrasonic transverse wave propagation. Finite element modeling was performed to ascertain how the results agree with the numerical method. Ultrasonic transverse wave velocities on the LR, LT, and RT planes were decreased from 1347, 1323, and 589 m × s-1 to 1286, 1269, and 561 m × s-1 when relative humidity increased from 45 % to 85 % at a constant temperature of 20 ± 1 °C, respectively. The dynamic and static shear modulus on the LR, LT, and RT planes were decreased from 988, 953, and 189, and 966, 914, and 182 MPa to 927, 903, and 176, and 845, 784, and 154 MPa when relative humidity increased from 45 % to 85 % at a constant temperature of 20 ± 1 °C, respectively. Therefore, both velocity and modulus values at all principal axes and planes were decreased with an increase in moisture. Maximum (15.2 %) and minimum (2.3 %) differences between dynamic and the static shear modulus were observed for GLT at 85 % and GLR at 45 % relative humidity, respectively. Coefficients of determinations between the dynamic and static shear moduli were ranged from 0.68 (GLR at 65 % RH) to 0.97 (GLR at 85 % RH). Finite element analysis, only for 65 % RH values, was performed using Solid 45 element, and, according to results, load-deformation curves created by linear orthotropic material properties, are well-matched with the static curves.