Experimental Investigation of the Static and Dynamic Compression Characteristics of Limestone Based on Its Initial Damage

In the current work a new equation for initial damage assessment of limestone based on plane strain theory is proposed. Detailed investigations of the static and dynamic characteristics of limestone with different initial damage degree, using longitudinal wave speed, and static-dynamic compression tests are performed. This study investigated the static and dynamic characteristics of limestone with different initial damage degree, using longitudinal wave speed, and static-dynamic compression tests. Experimental results show that the degree of initial damage decreases with increasing longitudinal wave speed, which reaches the minimum when the longitudinal wave speed is approximately 6000 m/s, and the smaller the longitudinal wave velocity, the greater the degree of initial damage. The static and dynamic compressive strengths of limestone increase with the longitudinal wave velocity and strain rate, but the elastic modulus and Poisson’s ratio do not change significantly. Finally, based on the experimental results, the definitions of damage threshold value and strain softening are proposed, which further verify the influence of strain rate and initial damage on rock compression characteristics. The present study sheds light on the importance of initial damage for the mechanical state of rock in underground engineering.

Nonlinearity in Ultrasonic Guided Waves Propagation in Solids Under Constrained Thermal Expansion

Finite strain theory has been employed in the past to mathematically describe nonlinear wave propagation phenomena such as acoustoelasticity (wave speed dependency on quasi-static stress), wave interaction, wave distortion, and higher-harmonic generation. The present work expands the topic of nonlinear wave propagation to the case of a constrained solid subjected to thermal loads. In this framework, the anharmonicity of interatomic potentials, and the absorption of the potential energy corresponding to the (prevented) thermal expansion, are identified as sources of nonlinear effects. Such “residual” energy is, at least, cubic as a function of strain, hence leading to a nonlinear wave equation and higher-harmonic generation. Closed-form solutions are given for the longitudinal wave speed and the second-harmonic nonlinear parameter as a function of interatomic potential parameters and temperature increase. According to the proposed model, the prevented thermal expansion of the solid leads to thermal stresses that, in turn, produce a decrease in longitudinal wave speed and a corresponding increase in nonlinear parameter with increasing temperature. Experimental measurements of the ultrasonic nonlinear parameter on a steel block under constrained thermal expansion confirm this trend. Emphasis is placed on the potential of a nonlinear ultrasonic measurement to quantify thermal stresses from prevented thermal expansion. This knowledge can be extremely useful to prevent thermal buckling of various structures, such as continuous-welded rails in hot weather.

Calculation and Analysis of Loss Factor of Building Materials

In order to describe the damping characteristics of building materials and members, the formula for calculating loss factor which concerns with the internal loss factor and edge losses was derived from the concise physical relationship and, calculations of loss factor of some common building materials and members are presented. Therefore, the loss factor curves of among the walls which made of different materials are gained. It is shown that at low frequency total loss factor (damping) of a building material gradually decreases with the frequency and is also dependent on the thickness of the wall and its longitudinal wave speed, and at high frequency it tends to a constant.

Transverse Impact Response of a Linear Elastic Ballistic Fiber Yarn

Transverse impact response of a linear elastic Kevlar® KM2 fiber yarn was determined at various striking speeds from Hopkinson bar and gas gun experiments incorporated with high-speed photography techniques. Upon transverse impact, a triangle shape was formed in the fiber yarn. Both longitudinal and transverse waves were produced and propagated outwards the fiber yarn. Both the angle of the triangle and Euler transverse wave speed vary with striking speeds. The relationship between the Euler transverse wave speed and the striking speed was determined. The transverse impact response of the fiber yarn was also analyzed with a model, which agrees well with the experimental results. The model shows that the longitudinal wave speed is critical in the ballistic performance of the fiber yarn. At a certain striking speed, a higher longitudinal wave speed produces a higher Euler transverse wave speed, enabling us to spread the load and dissipate the impact energy faster, such that the ballistic performance of the fiber yarn is improved.

Self-Sustained Fracture Waves in Soda-Lime Glass

High-speed framing photography in conjunction with circularly polarised light has been employed to monitor qualitatively the state of residual stress in Prince Rupert’s drops of soda-lime glass undergoing disintegration by a self-sustained fracture wave in the glass drops. It is revealed that the fracture wave through a Prince Rupert’s drop is driven by the residual stress in the drop, with the propagation speed of the fracture wave being (1700 ± 100) ms-1, which is close to the terminal speed of individual cracks in the soda-lime glass, but is much smaller than the longitudinal wave speed of 5300 ms-1 in the glass. These observations support our recently reported observations and also give support to our conclusions that the fracture wave speed of a self-sustained fracture wave is equal to the terminal speed of individual cracks in the glass. Some preliminary observations from fracture waves in Prince Rupert’s drops of a lead oxide glass are also described, which show that in Prince Rupert’s drops of the lead oxide glass the fracture wave is also self-sustained and it travels through the drop at a steady and stable speed of (1300 ± 100) ms-1, which is also considerably smaller than the longitudinal wave speed of 4800 ms-1 in the lead glass. A brief comment is also made on the fracture waves observed by other workers in brittle oxide glasses and solids generated by plate impacts and shock waves.