A Unified Strength Model of Asphalt Mixture Considering Temperature Effect

The strength characteristics of asphalt mixture is crucial for the design and construction of asphalt roads. A strength model considering the effect of temperature is presented in this paper based on unified strength theory (UST). Firstly, direct tensile tests, uniaxial compression tests and anti-shear property tests of asphalt mixture were carried out respectively at different temperatures. Key mechanical parameters were obtained, including tensile strength (σt), compressive strength (σc) and shear strength (τ0) at different temperatures. Besides, the temperature sensitivity of σt, σc and τ0 was systematically analyzed. The results showed that the UST parameters of tensile-compression strength ratio α and failure criterion parameter b have a linear relationship with temperature t. A theoretical model to describe strength characteristics with the temperature of asphalt mixture was developed finally. The developed model was validated via applicability analysis. and it will provide theoretical support for the study of strength characteristics of asphalt mixture and engineering practice.

Effects of Grain Pattern on the Rolling Shear Properties of Wood in Cross-Laminated Timber

Rolling shear modulus and strength are the key factors affecting the mechanical performance of some wood products such as cross-laminated timber (CLT). As reported, rolling shear property strongly depends on the sawing pattern such as the aspect ratio and grain direction (grain mode). However, the mechanism behind this phenomenon has not yet been clarified. In this work, the rolling shear modulus and strength of spruce-pine-fir (SPF) with different grain modes and aspect ratios were experimentally investigated. In addition, a theoretical investigation was carried out to reveal the mechanism behind this phenomenon. The results exhibited that the rolling shear moduli of 0° and 90° grain-mode wood were the same. This value can be called the pure rolling shear modulus. Rolling shear modulus of wood with angles other than 0° and 90° can be calculated from the pure rolling shear modulus and grain angle. Therefore, this modulus can be called the apparent rolling shear modulus. Thus, using 0° and 90° grain-mode specimens to determine the pure rolling shear modulus and strength of wood is recommended.

Experimental method and evaluation for interlaminar shear properties of randomly oriented strand thermoplastic composites based on modified double-notch specimen and two dimensional digital image correlation

A new interlaminar shear test method has been proposed based on the double-notch compression test method, in which the test specimen shape with a modified overlap length of the notches is proposed, and the interlaminar shear strain is measured by two-dimensional digital image correlation (2D-DIC) analysis. In order to obtain the interlaminar shear properties in the elastic and non-linear regions of randomly oriented strand thermoplastic composites, we adopted a 2D-DIC analysis system using a bi-telecentric lens, which can accurately measure the strain in a small field of view, and a test system including an interlaminar shear test jig, which can apply a compressive load to the end face of the specimen at high perpendicularity. It is necessary to provide an overlap of the double-notch of 1 mm or more in order to simultaneously obtain the strain in the elastic region and the non-linear region from the actual test results. When numerical analysis by finite element method (FEM) was carried out on four types of test specimen with different shapes used in this research, by using the interlaminar shear property data obtained from actual tests on the optimum test specimen, there was a high level of agreement with the 2D-DIC analysis results for the shear stress – strain diagrams and the interlaminar shear strain distribution. Therefore, the benefits of the test specimen shape and dimensions in the new test method and the validity of the interlaminar shear property values that can be obtained using this method have been confirmed.