Peculiarities of the Power Hydrocannon Operation

The paper is concerned with improvement of the devices for formation of super high-speed fluid jets termed hydro cannon. Two modes of the energy injection into the fluid (the piston impact and the powder explosion) are considered and advantages of the use of the gunpowder are determined. A numerical technique for prediction of the jet formation, developed previously by one of the authors is applied for description of the velocity and pressure fields within the hydro cannon. Effect of the design parameters on the fluid acceleration is explored and suggestions for improvement of the hydro cannon design are made.

Preliminary Experiments for Evaluating 3-D Effects on Cracks in Frozen Stress Models

Information gleaned from applying the frozen stress photoelastic method to cracks emanating from critical locations around the fin tips in models of solid rocket motors is reviewed and assessed together with new experimental results. The studies are the initial part of a program developed to contribute background data for consideration in modifying current motor grain design rationale.

Effective Stress Intensity Factor in Mode III Crack Growth in Round Shafts

Turbine-generator shafts are often subjected to a complex transient torsional loading. Such transient torques may initiate and propagate a circumferential crack in the shafts. Mode III crack growth in turbo-generator shafts often results in a fracture surface morphology resembling a factory roof. The interactions of the mutual fracture surfaces result in a pressure, and a frictional stress field between fracture surfaces when the shaft is subjected to torsion. This interaction reduces the effective Mode III stress intensity factor. The effective stress intensity factor in circumferentially cracked round shafts is evaluated for a wide range of applied torsional loadings by considering a pressure distribution in the mating fracture surfaces. The pressure between fracture surfaces results from climbing the rought surfaces respect to each other. The pressure profile not only depends on the fracture surface roughness (height and width (wavelength) of the peak and valleys), but also depends on the magnitude of the applied Mode III stress intensity factor. The results show that the asperity interactions significantly reduce the effective Mode III stress intensity factor. However, the crack surfaces interaction diminishes beyond a critical applied Mode III stress intensity factor. The critical stress intensity factor depends on the asperities height and wavelength. The results of these analyses are used to find the effective stress intensity factor in various Mode III fatigue crack growth experiments. The results show that Mode III crack growth rate is related to the effective stress intensity factor in a form of the Paris law.

Dynamic Pipe Stresses During Water Hammer: V — Applications

Theoretical equations to describe dynamic stresses during water hammer were developed in the first four parts of this series of papers, and this fifth paper applies those equations to analyze piping failures in a nuclear waste facility. The pipe failures were shown to be coincident to valve closures and pump shut downs, which caused fluid transients in the system. Magnitudes of the pressure increases during the transients were calculated and implemented in dynamic stress analyses for the piping. The maximum pipe stresses were then compared to the fatigue stresses of the pipes, and the failure mechanisms were thus established. By slowly closing valves, the effects of the fluid transient can be nearly eliminated. Using the closed from equations, the minimum time of valve closure may be calculated to prevent recurrent pipe failures. This application of the original closed form solutions provides further insight into the use and validity of the new dynamic stress equations.

Dynamic Stresses During Structural Impacts

Dynamic stresses that occur when an object strikes a structure can be described by considering both vibration theory and conservation of energy principles. An object striking a simple beam is used as one of several examples. The complete stresses are found by adding the stresses obtained from a vibration equation to the stresses found by using a conservation of energy equation. When combined, these two stresses establish the maximum stress in a structure subject to impact. This solution assumes that each point within the beam acts as a linear system, reacting to the dynamic application of a load to the structure. When struck, the surface of the beam is momentarily compressed, and the beam bends. The equations describe both the localized stresses at the point of impact and the bending stresses in the beam following impact. These equations are then extended to an elastoplastic case, using a bilinear model to describe the dual natured linear elastic and linear plastic material behavior. The general solution technique is applicable to cases other than the simple beam.

A Proper Groove Design for Distortion Control of the Multi-Pass Weldment at Pressure Vessel

The purpose of this study is to establish a proper groove design for multi-pass butt weldment with narrow groove of pressure vessel to control welding distortion. To do it, the behavior of angular distortion and longitudinal shrinkage force of the simple butt weldment were evaluated using a finite element analysis and experiment. The effective bending rigidity of the multi pass butt weldment with welding pass was defined as a function of the effective thickness of weld throat. Based on the results, the predictive equations for the welding distortion of the multi-pass both side weldment were established as function of heat input and effective bending/in-plane rigidity of the weldment. Using the equation, a proper ratio of the groove height can be determined to control the distortion for the multipass both side weldment with reference to various groove shape and plate thickness.

Studies of Hydrogen Embrittlement Effects on Steel Pipeline Used for Natural Gas Transport

A steel pipeline containing niobium, vanadium and titanium as microalloying elements was tested for hydrogen embrittlement. Hydrogenated specimens intercritically annealed at relatively low temperature to develop martensite islands in a ferrite matrix basically exhibited quasi-cleavage fracture with some ductile dimpling. The objective of this investigation, carried out by the principal investigator is to study the mechanical properties and susceptibility to hydrogen embrittlement effects on steel pipeline used for natural gas transport.

Multi-Scale Approach for Nonhomogeneous Microstructural Effects on Damage in Particulate Composites

This study investigated the effects of random and non-uniform particle distributions on the damage initiation and growth in particulate composites. Numerical specimens with either no crack or an existing crack were examined. For the cases with no crack, the effect of sizes of the representative area for non-uniform particle volume fractions was studied on the overall stress-strain curves and the results were compared with that of the specimen with uniform particle volume fractions. Other studies considered cracked specimens, either single edge crack or a center crack. The global-local approach was used along with multi-scale technique. The global analysis determined the deformations around the crack tip. Then, the local analysis evaluated the damage progress at the crack tip using the solution of the global analysis as boundary conditions. The results showed non-uniformed particle volume fractions in particulate composites caused the crack growth at lower applied loads than the uniform particle volume fraction. Statistical data were also plotted for the non-uniform particle volume fraction cases.

Investigation of Microcrack Growth in [0/90]s Composite Laminates

Techniques such as optical microscopy and X-radiography have provided useful information regarding damage in composite laminates, particular in therms of microcracking behavior in individual plies. This focuses on the investigation of microcracking and damage evolution in loaded composite laminates via X-ray computed microtomography. The main advantage in the use of such a technique is that damage within the composite can be assessed in three-dimensions without destruction of the composite. In this work, IM7/977–2, IM7/5555, and IM7/5276-1 coupons were uniaxially tested in a tensile substage, Graphs that convey microcracking density information as a function of applied load were created for [0/90/90/0] laminates. The three dimensional geometry and connectivity of microcracks and other damage in these samples were investigated through microtomographic reconstruction.

Surface Topology Optimization of Water Tanks Using Genetic Algorithm

The purpose of this work is to explore the possibility of utilizing Genetic Algorithm in optimizing the surface topology of water tanks. The surface characteristics of a corrugated tank are tested on a small element on its circumference. A mathematical equation to represent most practical corrugated surfaces is developed using the Coons surface with trigonometric series curves. The parameters of this mathematical equation are used to describe the chromosome for different surfaces. A multi-objective fitness function incorporating the performance of a surface and the manufacturing cost associated with that surface is developed, which uses finite element analysis to determine the performance of each surface. Considerable better corrugations, compared to those normally used, were found.