Experimental Study on the Law of Energy Dissipation and Damage in Coal Body Based on Local Tensile-Sliding Effect

The slippage initiation and induced instability of roadway surrounding rock are highly likely to cause dynamic disasters, severely influencing the safety production of mining. With the optical-mechanical monitoring test of the deformation localization of energy dissipation, this study established the optical index of coal deformation equilibrium degree under load, and obtained the evolution law of coal deformation equilibrium degree. After analyzing the relationship between tensile-sliding effect and mechanical behavior of coal deformation field, it proposed the strain energy ratio coefficient. The results indicate that the strength reduction of coal body is affected by the deformation accumulation of loading displacement field. The sliding displacement of the stable sliding type specimen occurs 5.5s earlier than tensile displacement，which is 4.4s longer than the instantaneous instability type specimen. The instability type of coal is closely related to the tangent angle of the strain energy ratio coefficient and the damage persistence characteristics. The damage accumulation of stable equal amplitude contributes to the stable failure, and the damage accumulation of interval equal amplitude influences the instantaneous instability development. The fracture expansion stage is the main stage of energy consumption damage accumulation. That is, the main energy consumption damage accumulation stage of the stable slip coal is the stable crack expansion stage, with the damage proportion of 35.89%, while the damage proportion of instantaneous instability coal in the unsteady crack expansion stage is 84.226%. The study provides theoretical reference for the fracture law and risk monitoring of coal slippage.

Metal–plastic composites with amplitude-dependent constraint layer damping

For metal–plastic composites with thin shear-sensitive cores, high damping can be determined. These materials were developed to reduce the structure-borne noise and are therefore used for thin-walled components with bending loads. In addition to the known sensitivity due to the temperature and frequency, these materials show a significant dependency on vibration amplitudes. Within the framework of this study, the nonlinear damping of metal–plastic composites was determined experimentally using free-vibrating cantilever beams. A detailed analysis of the derived velocity–time curves showed a nonlinear damping within the decay. An exponential approach was successfully used to describe the relation between damping and current deflection. Furthermore, a strain energy-based evaluation is introduced to quantify the share of the core contributions. For this purpose, the strain energy of several acoustically sensitive car components as well as the beams with varying supports and vibration lengths were determined numerically with a finite element analysis. The strain energy ratio of the cores was then derived as a comparative measurement and within a finite element-based design of experiments. A cantilever beam setup with a component-specific beam length representing similar core strain energy ratios was retested and showed a similar exponential amplitude dependence but higher damping parameters.

Analysis on vibration energy concentration of the one-dimensional wedge-shaped acoustic black hole structure

The transverse vibration energy of a plate with a wedge-shaped profile can be trapped by acoustic black hole effect to its edge portion, in case the wedge thickness is diminished according to the power-law h( x) = εxm with m ≥ 2.0. The acoustic black hole effect exhibits potential ability for passive vibration control and energy harvesting. In this article, the transfer matrix method is adopted to establish and solve the dynamical model of acoustic black hole structure. Energy ratio is defined as a ratio of the energy trapped within the edge portion to that of the whole wedge, to illustrate the energy concentration effect. Analyses show that both the strain energy ratio and kinetic energy ratio of the acoustic black hole structure achieve the minimum when the wedge is in resonances, although these two kinds of energy come to peaks at this case. However, in the case of small length of the edge portion, the strain energy ratio reaches the highest peaks at the second and higher resonances, rather than at the first one. Generally, the best effect of energy concentration occurs when m ranges from 2.5 to 3.0. Reducing the truncation thickness and increasing the maximum height can improve the energy trapping.

Performance Evaluation of Buckling-Restrained Braces Installed in a Mid-Rise Steel Structure

The authors have continuously studied buckling-restrained braces using steel mortar planks (BRBSM). The performance of energy absorption and fatigue against cyclic loading has been evaluated. Although past studies have clarified the structural performance of BRBSM as single member, it is necessary to study not only the performance of BRBSM as single member but also the performance of BRBSM installed in a building structure. In this paper, a frame model of mid-rise steel structure with BRBSM subjected to earthquake motions with various characteristics is analyzed. Comparing the results of the analysis and the past tests, the seismic behavior of a structure is discussed. Especially, the seismic performance of BRBSM installed in the building structure is evaluated. In addition, the seismic performance of two types of BRBSM; basic and developed high-performance types, is compared and evaluated about cumulative plastic strain energy ratio and cumulative fatigue. As a result, the performance capacities of the both types of BRBSM exceed the required values of BRBSM under severe earthquake motions about cumulative plastic strain energy ratio and cumulative fatigue. The basic-type BRBSM has the fatigue capacity against 2 to 5 times severe earthquake motions. The required values of high-performance-type BRBSM are about a half of accumulated fatigue capacity compared with the basic-type one. The high-performance-type BRBSM is applicable against quite many cyclic loadings of low strain amplitude, and able to be used for long-term service.

Research on Feasibility and Applicability of Delamination Localization Methods for Composite Laminated Beams

The feasibility and applicability of delamination damages localization methods with various defined damage indexes for the damaged composite laminated beam were studied. The results indicate that, for the modal strain energy method, damage indexes defined by strain energy difference are more effective to locate the delamination damage than that of strain energy ratio. For energy response method, damage index defined by the second difference can effectively locate the delamination damage in the composite laminated beams.

Free Vibration and Stability of a Spinning Disk-Spindle System

This work examines the free vibration and stability of a spinning, elastic disk-spindle system. The extended operator formulation is exploited to discretize the system using Galerkin’s method (Parker, 1999). The coupled vibration modes of the system consist of disk modes, in which the disk dominates the system deformation, and spindle modes, in which the spindle dominates the system deformation. Both the natural frequencies and vibration modes are strongly affected by disk flexibility. If the membrane stresses associated with disk rotation are neglected then the system exhibits flutter instabilities, but these instabilities are not present when membrane stresses are modeled. Natural frequency veering between disk and spindle frequencies is prominent at low speeds and substantially affects the spectrum and stability. No veering is observed at high speeds where rotational stress stiffening diminishes disk-spindle coupling and causes the natural frequencies to converge to those of a rotating spindle carrying a rigid disk. Changes to the vibration modes are examined in terms of a strain energy ratio measuring the contribution of the disk strain energy to the total modal strain energy.