Reduction of residual stresses in thick-walled composite cylinders by smart cure cycle with cooling and reheating

The nozzle parts of solid rocket motors must endure both the internal pressure generated by high temperature exhaust gas and the mechanical load generated by steering operation. Therefore, the nozzle parts of solid rocket motors are fabricated with thick carbon fiber phenolic resin composites. When the thick-walled phenolic composite cylinder is cooled down from the curing temperature of about 155 °C to the room temperature, thermal residual stresses are created due to the anisotropic thermal deformation of the composite structure.

In this paper, a smart cure method with cooling and reheating was developed to reduce residual stresses in thick-wound composite cylinders made of carbon phenolic woven composite. The optimal cure cycle was obtained to reduce the residual stresses without increasing processing time and applied to fabrication of the thick-walled composite cylinder. From the residual stresses measured by the radial-cut-cylinder-bending method, it was found that the residual stresses were reduced 30% by using the smart cure method.     

A comparison of liquid hydrocarbon calibration standards in piston cylinders and standard cylinders with eductor tubes

Natural gas liquid standards consist of various components primarily in the C1-C6 range; they are available in three types of cylinder packages: piston cylinders and two other types of standard cylinders with eductor tubes. The three cylinder packages have different operation conditions and thus a sample may behave differently in each of the packages. The piston cylinder maintains the components in a single liquid phase at a constant pressure, while the standard cylinders maintain the components as a two-phase mixture. Typically, the components may distribute between the two phases in different concentrations depending on the various thermodynamic variables, such as temperature, pressure, and volume. This study will examine the integrity of the sample in the three cylinder packages during a controlled cylinder depletion. The results for the various cylinders will be compared with a theoretical model of the experiments.     

Basic study on new cryogenic refrigeration using CO2 solid–gas two phase flow

In this paper, a cryogenic refrigeration method is described, which utilizes CO₂ solid–gas two phase flow and the dry ice. The CO₂ solid–gas two phase flow is achieved by expanding liquid CO₂ and thus refrigeration process less than CO₂ triple point −56.6 °C can be available. The experimental work is divided into two parts and two experimental set-ups were designed, constructed and tested. The interest of the first experiment test is the feasibility of expanding liquid CO₂ into CO₂ solid–gas flow in a horizontal circular tube by expansion valve. The second experiment focuses on the feasibility of the refrigeration of liquid CO₂ expanding into solid–gas two phase flows used in a prototype CO₂ heat pump system. The results show that solid–gas two phase flows can be achieved by expanding liquid CO₂ by expansion valve in a closed CO₂ heat pump system loop and low temperature refrigeration below −56.6 °C is achieved in the experiments, which give greater possibility to create a cryogenic refrigeration process below −56.6 °C for food industries, bio-medical engineering, etc.     

Cracked semi-infinite cylinder and finite cylinder problems

This work considers the analysis of a cracked semi-infinite cylinder and a finite cylinder. Material of the cylinder is assumed to be linearly elastic and isotropic. One end of the cylinder is bonded to a fixed support while the other end is subjected to axial tension. Solution of this problem can be obtained by superposition of solutions for an infinite cylinder subjected to uniformly distributed tensile load at infinity (I) and an infinite cylinder having a penny-shaped rigid inclusion at z = 0 and two penny-shaped cracks at z = ±L (II). General expressions for the perturbation problem (II) are obtained by solving Navier equations with Fourier and Hankel transforms. When the radius of the inclusion approaches the radius of the cylinder, the end at z = 0 becomes fixed and when the radius of the cracks approach the radius of the cylinder, the ends at z = ±L become cut and subject to uniform tensile load. Formulation of the problem is reduced to a system of three singular integral equations. By using Gauss–Lobatto and Gauss–Jacobi integration formulas, these three singular integral equations are converted to a system of linear algebraic equations which is solved numerically.     

Measurement of residual stresses in thick composite cylinders by the radial-cut-cylinder-bending method

Thick fabric composite cylinders for nozzle parts in solid rocket motors should be designed to endure the extreme temperature and pressure of combustion gas. As the thickness of the composite cylinder increases, fabricational residual stresses due to the anisotropic thermal expansion or shrinkage of fabric composites also increase, which induces inter-laminar failures. Therefore, the accurate estimation of the residual stresses is indispensable for the development of thick fabric composite cylinders.

In this paper, the residual stresses in thick cylinders made of carbon fabric phenolic composites were measured by a new radial-cut-cylinder-bending method. To obtain the residual stresses from the measured relative strains during the radial-cut operation, a bending test of the cylinder with the radial-cut was performed instead of measuring the material properties with respect to radial positions. The thermal residual stresses were also calculated by finite element method considering shear deformation of fabric layers, and compared with the measured residual stresses by the new method, from which it was found that the new simple method estimated the residual stresses pretty well. Also the inter-laminar tensile strength at the position of maximum radial residual stress could be obtained from the bending test.     

Effect of negatively charged species on the growth behavior of silicon films in hot wire chemical vapor deposition

The deposition behavior of silicon in hot wire chemical vapor deposition was investigated, focusing on the generation of negatively charged species in the gas phase using a gas mixture of 20% SiH₄ and 80% H₂ at a 450 °C substrate temperature under a working pressure of 66.7 Pa. A negative current of 6–21 µA/cm² was measured on the substrate at all processing conditions, and its absolute value increased with increasing wire temperature in the range of 1400 °C–1900 °C. The surface roughness of the films deposited on the silicon wafers increased with increasing wire temperature in the range of 1510 °C–1800 °C. The film growth rate on the positively biased substrates (+ 100 V, + 200 V) was higher than that on the neutral (0 V) and negatively biased substrates (− 100 V, − 200 V, − 300 V). These results indicate that the negatively charged species are generated in the gas phase and contribute to deposition. The surface roughness evolved during deposition was attributed to the electrostatic interaction between these negatively charged species and the negatively charged growing surface.     

Analyses of the multiple cracking behaviour of brittle hollow cylinders under internal pressure

In order to elucidate the multiple cracking behaviour of brittle hollow cylinders under static internal pressure, two-dimensional dynamic finite element analyses have been performed firstly for graphite hollow cylinders with inner and outer diameter of 16 and 22 mm, respectively, under internal gas pressure. In the analyses, propagation speed of the primary crack was set to be extremely high by instantaneously releasing the nodes that defined the path of the primary crack, and internal pressure was preserved after the primary cracking. The analyses showed that the stress was enhanced due to stress waves generated by the primary cracking. The initial stress enhancement was observed at the side position of the cylinder, which was located at approximately ±90° with respect to the primary cracking site. This implied that secondary cracking could occur at the side positions. Fracture modes of the cylinders might depend on the following parameters: (1) propagation speed of the primary crack, (2) pressure drop rate after the primary cracking, (3) medium to generate internal pressure, (4) geometry of a cylinder, (5) mechanical properties of brittle materials, and (6) presence of a notch. Thus, the effect of the above parameters on the behaviour of the multiple cracking was also analysed. It was found that secondary cracking would still occur at the side positions if (i) the crack propagation speed was between 70% and 100% of the theoretical crack propagation speed, (ii) the pressure drop rate was below 10⁷ Pa/s, (iii) wall thickness of the cylinder was changed, and (iv) other brittle materials were employed. Also, it was found that multiple cracking would not be observed if liquid pressure was employed instead of gas pressure, because of fluid-structure interaction. In addition, the position of the secondary cracking would be shifted by introducing a notch on the outer surface of the cylinder. These results were in good accordance with experiments formerly reported.     

Effect of Mg and Sr-modification on the mechanical properties of 319-type aluminum cast alloys subjected to artificial aging

Aluminum-based 319-type cast alloys are commonly used in the automotive industry to manufacture cylinder heads and engine blocks. These applications require good mechanical properties and in order to achieve them through precipitation hardening, artificial aging treatments are applied to the products. The standard artificial aging treatment for alloy 319, as defined by the T6 heat treatment temper, consists in solution heat-treating the product for 8 h at 495 °C, water quenching at 60 °C, and then artificially aging at 155 °C for 2–5 h.

The present paper reports on aging heat treatments that were performed on four Al–Si–Cu–Mg 319-type alloys: 319 base alloy, Sr-modified 319 alloy, 319 alloy containing 0.4 wt% Mg, and the Sr-modified 319 + 0.4 wt% Mg alloy. This investigation was carried out in order to examine the effect of Sr-modification and additions of Mg on the microhardness, tensile strength and impact properties of 319-type alloys over a range of aging temperatures and times (150–240 °C, for periods of 2–8 h).

The results show that the best combination of properties is found in the Sr-modified alloy containing 0.4 wt% Mg (i.e. alloy 319 + Mg + Sr). Also, the optimum artificial aging temperature changes when Mg is present in the alloy.     

La2Zr2O7 films on Cu–Ni alloy by chemical solution deposition process

Films of La₂Zr₂O₇ (=LZO) have been formed by chemical solution deposition technique (CSD) on new bi-axially textured Cu–Ni alloy tapes based on rolled constantan (Cu₅₅Ni₄₅) Rabits. The precursor used was acetylacetonates treated in propionic acid (0.1–0.87 mol/l) and then deposited by spin-coating. The LZO film starts to crystallize above 850 °C, the film nucleates bi-axially textured on the substrate (with unit cell axis rotated 45° from those of the substrate). The top part of the film is not textured even after long annealing time at 1100 °C, but the interfacial part is bi-axially textured. Thus, synthesis of bi-axially textured films on Cu₅₅Ni₄₅ Rabits seems possible but more works are needed to optimize its properties.     

Microstructural and mechanical properties evolution of magnesium AZ61 alloy processed through a combination of extrusion and thermomechanical processes

In this work, the microstructures and tensile properties of a commercial magnesium alloy “AZ61” processed by a combination of hot extrusion and thermomechanical processing (TMP) were investigated. The TMP was consisting of two or three hot rolling steps with large reductions per pass, thus allowing significant grain refinement. The microstructural evolution has been studied by means of optical and scanning electron microscopes, as well as X-ray diffraction analysis. The as-cast material is extruded in the form of a cylinder with initial diameter of 250 mm to a final diameter of 110 mm (80% reduction in cross-sectional area). Then hot rolling regimes were performed at 300 °C with different percentage of strain per pass. Tensile and hardness tests were performed in the samples (as-cast, extruded, and rolled) at room temperature in order to evaluate the mechanical properties of the material. The results of experiments demonstrated that fine grain size might be achieved in magnesium alloy AZ61 by using a two-step processing route involving an initial extrusion step followed by thermomechanical processing with large reduction in thickness per pass. This two-step process, designed to achieve average grain sizes of 10–20 μm.     

Electronic irradiation modification in parent Fe–Ni–C austenite and Snoek-like effects in induced alpha-martensite

Considerable changes in atomic distribution, Ni atomic ordering and elimination of inhomogeneity in distribution of carbon atoms in the -martensite occurred after high-dose electronic irradiation and subsequent deep cooling of parent Fe–22.4 at.%Ni–5.13 at.%C austenite in liquid nitrogen. These atomistic changes resulted from the electronic irradiation caused a huge increase of the 160 °C peak of internal friction in the -martensite. Discussion regarding this phenomenon brings to a conclusion on the behavior of the 160 °C peak, fitting in the best way for a certain Snoek-like relaxation in Fe–Ni–C martensite.     

Internal friction associated with phase transformation of nanograined bulk Fe–25 at.% Ni alloy

The internal friction and modulus of a nanograined bulk Fe–25 at.% Ni prepared by an inert gas condensation and in situ warm consolidation technique were measured in temperature range −100 to 400 °C by means of a dynamic mechanical analyzer (DMA). An internal friction peak at around −75 °C associated with martensitic transformation was observed. During heating, an internal friction peak at about 200 °C accompanied with the decrease of modulus was also observed, which was proved by XRD that this may mainly be attributed to the reverse phase transformation of stress-induced martensite (SIM). Some abnormal features of modulus versus temperature were observed and discussed.     

Effect of fiber orientation on the structural behavior of FRP wrapped concrete cylinders

In this study, 27 concrete cylinders with a diameter of 152.4 and a height of 304.8 mm were prepared. Among them, 18 cylinders were wrapped using two layers of fiber reinforced polymer (FRP) with six fiber orientations; six cylinders were wrapped using four layers of FRP with fibers in axial or hoop direction only; the remaining three cylinders were used as control. The FRP used was E-glass fiber reinforced ultraviolet (UV) curing vinyl ester. Fifteen coupon specimens were prepared to experimentally determine the tensile strength of the FRP with fibers oriented at 0°, 45°, and 90° from the loading direction. Co-axial compression tests were conducted on the wrapped cylinders and control cylinders. The test results were compared with existing confinement models. It is found that the strength, ductility, and failure mode of FRP wrapped concrete cylinders depend on the fiber orientation and wall thickness. Fibers oriented at a certain angle in between the hoop direction and axial direction may result in strength lower than fibers along hoop or axial direction. A larger database is desired in order to refine the existing design-oriented confinement models.     

气缸式蓄能器对压裂泵流体脉动的抑制作用

针对压裂泵流量脉动较大带来的问题,在分析压裂泵脉动产生机理及其特点的基础上,设计可用于高压大流量场合中的气缸式蓄能器,建立气缸式蓄能器回路数学模型,得到脉动流量的幅频特性,仿真研究脉动抑制特性的影响因素,并对压裂泵安装气缸式蓄能器前后的脉动流量进行对比分析,结果表明:气缸式蓄能器可用于高压大流量场合中,其脉动抑制特性随气缸预充气压力、气缸直径、蓄能器连接管长度的增加而减弱,随气缸行程、蓄能器连接管直径的增加而增强;气缸式蓄能器能显著抑制压裂泵流量脉动,可将机械式三缸压裂泵的流量脉动由23.07%降至2.42%,将液压驱动式三缸压裂泵的流量脉动由33.33%降至3.22%;研究结果为高压蓄能器的设计和使用提供了一种新的思路和方法。     

Risks of Fire and Explosion Associated With the Increasing Use of Liquefied Petroleum Gas

Liquefied petroleum gas (LPG) has been in use as household fuel all over the world for several decades. Until the late 1980s, its use in the developing world was largely confined to the economically well-off strata of the society but it has since spread over a much larger catchment. The increasing use of LPG has enhanced and generalized the risk of a “boiling liquid expanding vapor explosion” (BLEVE). This is evidenced from the reports which appear now and then of a LPG cylinder having exploded in a household, some workshop, or on a bus or a train. In fact some very major tragedies have been triggered by such explosions which also set off fires and cause secondary accidents. This paper describes what BLEVEs are and how can they be controlled. The paper focuses on hazards of BLEVE in large installations which deal with LPG, and other pressure-liquefied gases and discusses the nature, mechanism, and means of control of BLEVEs.     

Permeation of captan through disposable nitrile glove

The purpose of this study was to investigate the permeation of an aqueous emulsion of the pesticide, captan, as a wettable powder (48.9% captan) through a disposable nitrile glove material using an American Society for Testing and Materials (ASTM)-type I-PTC-600 permeation cell. The goal was to investigate the protective capability of the gloves against dermatitis. The analytical method was based on gas chromatography–mass spectrometry (GC–MS) and gas chromatography–electron capture detection (GC–ECD). The least quantifiable limit (LQL) was 6 ng for GC–ECD and 30 ng for GC–MS. Testing was conducted using the ASTM F739 closed-loop permeation method and a worst-case aqueous concentration 217 mg/ml of captan 50-WP. The average permeation rates were low, with 12±5 ng/(cm² min) after 2 h, 50±25 ng/(cm² min) after 4 h, and 77±58 ng/(cm² min) after 8 h. The calculated diffusion coefficient was (1.28±0.10)×10⁻⁵ cm²/h. No significant swelling or shrinkage occurred at P≤0.05. Infrared (IR) reflectance analysis of pre- and post-exposure glove surfaces confirmed no outer or inner surface degradation. The disposable nitrile glove showed excellent resistance to a highly concentrated aqueous emulsion of captan. Because the ASTM normalized breakthrough detection time of 250 ng/cm² was <2 h, these gloves should not be reused once worn, and decontamination is not advised. Protection is also advised for agricultural reentry field workers, because captan has been shown to persist on crops with a half-life greater than the current reentry intervals of 1–4 days.     

Optimized transcritical CO2 heat pumps: Performance comparison of capillary tubes against expansion valves

A capillary tube based CO₂ heat pump is unique because of the transcritical nature of the system. The transcritical cycle has two independent parameters, pressure and temperature, unlike the subcritical cycle. In the present study, a steady state simulation model has been developed to evaluate the performance of a capillary tube based transcritical CO₂ heat pump system for simultaneous heating and cooling at 73 °C and 4 °C, respectively against optimized expansion valve systems. Capillary tubes of various configurations having diameters of 1.4, 1.5 and 1.6 mm along with internal surface roughness of 0.001–0.003 mm have been tested to obtain the optimum design and operating conditions. Subcritical and supercritical thermodynamic and transport properties of CO₂ are calculated employing a precision in-house property code.

It is observed that the capillary tube system is quite flexible in response to changes in ambient temperature, almost behaving to offer an optimal pressure control. System performance is marginally better with a capillary tube at higher gas cooler exit temperature. Capillary tube length turns out to be the critical parameter that influences system optimum conditions. A novel nomogram has been developed that can be employed as a guideline to select the optimum capillary tube.     

Some studies on stresses and strains of aluminium alloy during extrusion-forging at room temperature

The present investigation has been undertaken to evaluate some aspects on extrusion-forging during cold upsetting using a suitable die using aluminium alloy (H9-6063) solid cylinders subjected to different geometrical conditions such as approaching angles namely, 35°, 45°, 50° and 60°, with two different initial protrusion heights namely 8 mm and 10 mm. During the experiments, three geometries such as barreled cylinder, truncated cone part and protruded part or extruded parts were observed. The calculations were made on the assumption that the volume constancy principle holds on and the curvatures of the barrel were in the form of a circular arc. Further, it is established that the protrusion height increases with the increase in the approaching angle for a given extrusion load. The relationship was also established between the various bulge parameters namely the hoop stress, the hydrostatic stress and the stress ratio parameters. In this work an attempt has been made to establish a relationship between the approaching angle and protrusion height and to establish a relationship among various height strains and stress ratio parameters.     

Optical properties of Si–O–N–F films as a phase shift mask material for 157 nm optical lithography

Si–O–N–F has been studied as a new candidate material for a high transmittance attenuated phase shift mask (HT-Att-PSM). The requirements of HT-Att-PSM are 20 ± 5% transmittance and 180° phase shift at the exposure wavelength (157 nm) and less than 40% transmittance at the inspection wavelength (193 nm). Si–O–N–F films were deposited with varying process parameters, such as gas flow rate and deposition time, to find optimum conditions to meet the above requirements. In this study, the effects of process parameters on the optical properties and the degradation of Si–O–N–F films were examined. To satisfy the requirements of HT-Att-PSM, a new mask structure was suggested and analyzed.     

标准气体气瓶体积膨胀的精确测量

目前普遍采用称量法制备标准气体,在此过程中气瓶体积膨胀所引入的空气浮力的不确定度贡献不可忽视。设计了一个气瓶充气膨胀率测量装置,该装置可以控制气瓶内充入气体的压力,并利用精密移液管测量气瓶体积的膨胀量,从而准确计算出气瓶的充气膨胀率。利用该装置对国内常见的2L、4L和8L铝合金气瓶进行了测量,结果显示气瓶体积的膨胀与充入气体的压力近似成线性正相关。而且气瓶外观体积越大,充气膨胀率的数值越大,量值之间也呈现出较强的相关性。基于获得的气瓶充气膨胀率数据,可以进一步降低气瓶体积膨胀对瓶内充入气体质量的不确定度贡献,从而使气体质量的计算更加精确。