Self-designed Testing System Research Articles

Investigation of hydroxyl-terminated polybutadiene propellant breaking characteristics and mechanism impacted by submerged cavitation water jet

A submerged cavitation water jet (SCWJ) is an effective method to recycle solid propellant from obsolete solid engines by the breaking method. Solid propellant’s breaking modes and mechanical process under SCWJ impact are unclear. This study aims to understand those impact breaking mechanisms. The hydroxyl-terminated polybutadiene (HTPB) propellant was chosen as the research material, and a self-designed test system was used to conduct impact tests at four different working pressures. The high-speed camera characterized crack propagation, and the DIC method calculated strain change during the impact process. Besides, micro and macro fracture morphologies were characterized by scanning electron microscope (SEM) and computed tomography (CT) scanning. The results reveal that the compressive strain concentration region locates right below the nozzle, and the shear strain region distributes symmetrically with the jet axis, which increases to 4% at first 16th ms, the compressive strain rises to 2% and 6% in the axial and transverse direction, respectively. The two tensile cracks formed first at the compression strain concentrate region, and there generate many shear cracks around the tensile cracks, and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks, forming the tensile-shear cracks and the impact parts eventually fail. The HTPB propellant forms a breaking hole shaped conical after impact 10 s. The mass loss increases by 17 times at maximum, with the working pressure increasing by three times. Meanwhile, the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole. The breaking efficiency is closely affected by working pressures. The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.

Effect of steam on the creep behavior of T92 steel at 650°C

One self-designed testing system was utilized to investigate the creep behavior of the T92 steel in steam environment. The creep tests were conducted at 650 °C with a certain stress range from 100 MPa to 160 MPa in the steam environment and air respectively. The specimens tested in steam environment shows typical multi-layered oxide scale consists of an outer scale of magnetite and an inner scale of Cr-rich spinel. Compared to the specimens in air, the steam specimens possessed larger minimum creep rate and reduced plasticity. The stress dependence of minimum creep rates exhibited a power law with similar exponents of 12.0 and 12.6 in steam environment and air respectively, indicating similar operating mechanism of creep. However, the activation energy in steam environment was smaller than that in air. Microstructural observation demonstrated that the degradation of tempered martensite lath structure and coarsening of the precipitations were mainly responsible for creep damage both in steam environment and air. The results concentrating on the possible interaction between the oxidation scale growth process and creep were discussed on the basis of oxidation process, a potential effect of hydrogen on creep and potential hydrogen embrittlement.

Impacts of confining pressure and safety thickness on water and mud inrush in weathered granite

Due to the strong disintegration and water erosion of completely weathered granite, water and mud inrush disasters are apt to take place in this zone during underwater tunnel construction. The pore, compactness, seepage path length, fracture geometries and their interconnections for water and mud transfer are strongly influenced by confining pressure and waterproof-resistant slab safety thickness. In order to inspect the influence, a series of experiments based on a self-designed testing system and non-Darcy testing method were performed. The results indicated that the water and mud inrush evolution increased with the increase of confining pressure and decreased with the increase of safety thickness. In particular, the confining pressure mainly influences the initial evolution stage, and a critical safety thickness to prevent water and mud inrush is obtained. Besides, the non-Darcy testing method results shows that the water and mud inrush evolution affects the influence of non-Darcy flow. For example, while the safety thickness was smaller than the critical value, the evolution was large and unstable and its behavior transferred into nonlinear. In this case, the flow changed to non-Darcy flow.

Analysis and experiment on cutting performances of high-stubble maize stalks

In the cold areas of Northeast China, maize high-stubble cutting is a novel stalk conservation tillage method, in which the maize stalks are under a unilaterally-fixed no-support cutting status. Thus, reducing the cutting resistance and power consumption of maize stalks under this status is very significant for development of high-efficiency high-stubble cutting devices. Based on a self-designed testing system that highly restored the maize high-stubble cutting conditions and by means of experimental design and mathematic statistics, the effects of working parameters (blade angle, blade shape, cutting speed and cutting angle) on the maximum cutting resistance and power consumption were studied. By analyzing stress conditions during the stalk cutting process, six mathematic models were built to express the relationships between individual factors and the maximum cutting resistance or cutting power consumption. Through model optimization, the parameter combination for optimal cutting performance of maize stalks under unilaterally-fixed no-support cutting status was obtained: blade angle is 18°, blade shape is isosceles triangle, cutting speed is 9.5 m/s, and cutting angle is 75°. Field validation experiments under this parameter combination showed that the maximum cutting resistance was (55.23±3.50) N (declined by 11.04%), and power consumption was (11.41±1.04) J (declined by 16.65%). The research findings can be a reference for the design and development of maize high-stubble cutting devices. Keywords: cutting performances, blade angle, working parameters, high-stubble, conservation tillage, mechanism analysis, corn DOI: 10.3965/j.ijabe.20171001.2589 Citation: Zhao J L, Huang D Y, Jia H L, Zhuang J, Guo M Z. Analysis and experiment on cutting performances of high-stubble maize stalks. Int J Agric & Biol Eng, 2017; 10(1): 40－52.

Water-resisting ability of cemented broken rocks

Using the self-designed testing system, the seepage tests for cemented broken rocks were conducted, and the impact of different factors on water-resisting ability was analyzed. The results show that (1) seepage process of the cemented broken rocks can be divided into two categories: in one category, seepage instability occurs after a period of time, in the other, the permeability decreases slowly and tends to be stable, and seepage instability does not occur; (2) cementing performance of cementing agent and grain size distribution are the decisive factors for water-resisting ability, with the increase of cementing performance and the mass percentage of large grains, the water-resisting ability of the specimen strengthens; (3) aggregate type has little effect on seepage stability, for the specimens with different aggregate types, the permeability and the duration of seepage instability have small difference; (4) initial porosity has a certain effect on the water-resisting ability of the specimen, but has no decisive role. With the increase of the initial porosity, the duration of seepage instability decreases.