Optimization of Forging Process Parameters and Prediction Model of Residual Stress of Ti-6Al-4V Alloy

Nonisothermal forging is an efficient plastic forming method for titanium alloys, but at the same time, it can produce large and uneven residual stress, which seriously affects the service life of components. In order to quantitatively analyze the influence of forging process parameters on the residual stress of Ti-6Al-4V alloy forgings, a numerical model was first established and optimized in combination with experiments. Then, the effects of deformation temperature, deformation degree, and deformation speed on the residual stress of forgings were analyzed by orthogonal test, and the optimal combination of forging process parameters was obtained. Finally, the multiple regression analysis was employed to propose multivariate regression models for the prediction of the average equivalent residual stress. Results show that the prediction model can be used for predicting the residual stress of Ti-6Al-4V alloy forgings with a higher reliability.

Stress Relief and Support for Stability of Deep Mining Roadway with Thick Top Coal in Hujiahe Coal Mine with the Risk of Rock Burst

Rock burst is a typical dynamic disaster in deep underground coal mining. Based on the support problems of the deep roadways in fully mechanized caving face 401111 of Hujiahe Coal Mine suffering from rock burst in Shaanxi Province of China, the failure law and influencing factors of the surrounding rock of the roadway are analyzed. The results show that the deformation of surrounding rock in the roadway shows the characteristics of elastic, plastic transformation, rheology, and expansion. At the same time, it has the typical characteristics of deep roadway, such as the fast deformation speed, long duration, asymmetric deformation, and large loose broken area of surrounding rock. Based on the principle of “strengthening support in shallow zones” and “deep pressure relief in deep zones” in the surrounding rock, the control scheme of surrounding rock in the return roadway of fully mechanized caving working face 401111 is proposed by taking the large diameter pressure relief and deep hole blasting as the main means of pressure relief. The practice shows that the surrounding rock of the return roadway is relatively stable after the implementation of the new scheme, which shows that the design of the new support scheme is reasonable and reliable. It is of great significance for the stability control of surrounding rock of the mining roadway suffering from rock burst.

On the Mechanical Behaviour in Stiffness Compensated Piezoelectric Beams - An Experimental Investigation Towards Energy Harvesting

In this work, a piezoelectric beam is stiffness compensated through adding a negative stiffness formed by attracting magnets. The mechanism’s purpose is low-frequency energy harvesting. The effect of deformation speed on the beam’s stiffness is investigated by force-displacement measurements taken at different speeds and with different load resistors connected. The effect of the load resistance on the beam’s stiffness has been found to be strongly dependent on the deformation speed. A load that results in the same stiffness as in a closed circuit at low deformation speed results in a stiffer response at a faster deformation speed. Also, when the beam is brought close to static balance with a certain load resistance connected, alteration of the load resistance has a great influence on the attained stiffness level. Furthermore, memory effects in the hysteresis found in piezoelectric actuators, related between input voltage and displacement, were also confirmed between displacement and force in sensor application.

Predictive assessment of the stability of quarry sides

The composition of the rocks composing the quarry sides and the approximate slope angles in accordance with the mining and geological conditions are described. The issues of creating observation stations are considered taking into account seasonal temperature fluctuations of the benchmarks. Observation materials are generalized, the degree of danger of deformations is established on the basis of observations of deformation speed. The mining safety control methods are described. The disadvantages of the approach to data processing and analysis are identified. A criterion for mine surveying prediction of the pit wall stability based on the comparison of critical and actual relative deformations is proposed. The purpose of the local forecast of wall deformation is to control the stability of non-working and working slopes of the sides, and to confirm the efficiency of the method used. The predictive assessment was carried out on the shift of working benchmarks on one of the open pits of Transbaikalia. It is suggested monitoring the stability of rocks using oscillograms obtained by seismic equipment.

Composite Materials Behaviour. Study, Development and Implementation of the Hypoelastic Model

The purpose of this research is to study and develop the formulation of a rheological law for composite materials with elasto-plastic behaviour in cold compression. Starting from the generally known relationships in literature, the hypoelastic model proposed for the composite materials behaviour (as powder materials) has been developped/explained, ensuring the understanding of the research. The hypolastic theory has been used for modeling the continuous transition from elastic to plastic state for a powder material. The material behaviour is described through an isotropic tensor relationship between the deformation speed tensor, Cauchy�s stress tensor and its derivative in relation to time (the Jaumann�s derivative). Only the linear part has been used from the general form of the law which depends on scalar functions. The calculations lead to relationships depending on five parameters which are identified according to experimental data. A numerical simulation of the stress-strain evolution during the simple compression of a diepressed powder sample is made; the numerical simulation has been validated by the experimental results.

Influencing Factors of Disturbance Effects of Blasting and Driving of Deep Mine Roadway Groups

The development and application of roadway group layout methods in coal mines have become more common and the mutual disturbance of blasting and driving of roadway groups has also become more prominent at depth. To improve the stability of rock mass surrounding roadways, we performed a systematic study on the factors that influence blasting and driving disturbances of adjacent roadways in deep mine roadway groups. We use the dynamic analysis module in FLAC3D to obtain the influence laws of three factors on the disturbance effects of adjacent roadways, namely, excavation methods, layer position changes of the roadway group, and whether or not bolt support is applied in the first roadway. Blasting strongly influences the surrounding roadway and increased horizontal distance can effectively reduce the disturbance effects of blasting and driving between adjacent roadways compared with increased vertical distance. Bolt support of the first excavated roadway enhances the roadway integrity and better stabilizes the rock structure surrounding the roadway. Industrial tests were carried out on three uphill roadways in the Gubei no. 1 mine (6-2). The monitoring results show that the movement of the roof and floor of the floor uphill return wind roadway is larger than that on the two sides. There is no notable change in the deformation speed of the surrounding rock in the floor return air roadway, but the deformation speed of the uphill conveyor belt roadway changes significantly. The results show that when the blasting excavation of a deep mine roadway group is more than five times the tunnel spacing, the increased horizontal distance effectively reduces the disturbance effects of excavation between adjacent roadways, which is consistent with the simulation results.

Configuration of Novel Experimental Fractographic Reverse Engineering Approach Based on Relationship between Spectroscopy of Ruptured Surface and Fracture Behaviour of Rubber Sample

A novel fractographic approach based on a combination of (i) mechanical behavior of cured rubber in uniaxial tensile loading and (ii) spectroscopy of fracture on a ruptured surface was experimentally validated. This approach related the migration of paraffin oil from a matrix to the ruptured rubber surface, to the tearing energy related to the deformation speed responsible for total rubber sample rupture, and the approach itself was configured experimentally. It was evaluated on cured natural rubber (NR) for two different paraffin oil concentrations. Single edge notched tensile (SENT) samples were subjected to uniaxial tensile loadings at two different deformation speeds. First, the tearing energy as a function of deformation speed was determined for each defined oil concentration. Secondly, at specific locations on the ruptured surfaces, infrared (IR) spectroscopy was performed to quantify a characteristic absorbance peak height of migrated paraffin oil during the rupture process. The results of the IR analyses were related to the deformation speed to understand the relation between the amount of migrated paraffin oil during the fracture process and the deformation speed which brought about such a fracture. This novel approach enhanced the reverse engineering process of rubber fracture related to the cause of tearing energies during critical failure.