International Journal of Advanced Design and Manufacturing Technology
Volume:5 Issue: 4, Sep 2012

An important issue in power generation and petrochemical industries is the monitoring of pipe wall thickness and corrosion/erosion rate. The pipes are usually subject to erosive and/or corrosive environments and any failure could be catastrophic. While periodic manual ultrasonic thickness measurement is the common practice in many industries, in certain cases, where higher accuracies are required, continuous monitoring systems are required. This paper introduces a measurement algorithm that can accurately measure the pipe wall thickness and estimate the pipe- wall thinning rate. The algorithm incorporates a model-based estimation technique for estimating the pipe wall thickness and thinning rate. It is an on-line non-intrusive ultrasonic thickness measurement tool for quick and accurate estimation of the erosion/corrosion rate and remaining pipe-wall thickness. The technique is applied to data measured from a pipe carrying high temperature liquid. The results show that the system can measure thinning rates as low as 10 µm/year within 5 days of data collection.

The global environmental concerns have put the light weighting of structures on the fore front of the research in transportation industry. Among other light weight alloys, the transportation industry is considering magnesium intensive light body-in-white structure in automotive applications. Although the research in modeling technique areas is very active, a suitable practical model mimicking the severe asymmetry and anisotropy of magnesium is lacking. Loading-unloading behavior of wrought magnesium alloy over a wide range of strain has been obtained experimentally and is presented here. It is shown that while the material behaves elastically isotropic, it shows a different yield in tension and compression with a high Bauschinger effect. This is attributed to the magnesium multiple deformation mechanisms of slip, extension/contraction twinning, and de-twinning resulting in an asymmetric yield and a direction dependent performance. Up-to-date there are no plasticity model commercially available that can capture these behavior. Therefore, it is necessary to develop a simple and efficient model that can serve as benchmarking tool for plasticity models evaluation. Such model is presented in this paper. The axisymmetric elastic-plastic model of Jahed and Dubey (1997) has been extended to wrought magnesium alloys. An asymmetric yield function is adapted and the obtained behavior in loading and unloading is directly incorporated in the solution process. It is shown that the results are significantly different from isotropic assumptions.

This research investigates the effect of the post-cure time on the residual stresses in laminated composites. Laminated composites were made of T300 carbon fibers and epoxy resin. The post-cure process was carried out at the constant temperature of 120 °C for 6 and 12 hours for two specimens. The slitting method was employed to determine through-thickness residual stress distribution of the composite laminates. The experiment results show that the increasing the post-cure time lead to the reduction of maximum residual stress as well as the uniformity of the residual stress distribution in laminated composites. Therefore, increasing the post-cure time is an effective way of reducing the destructive effects of residual stresses in laminated composites.

In this paper, an experimental and numerical investigation into the effect of the hoop welding in metallic pressure vessel is presented. In the experimental manufacturing, hoop welding was used to attach the cylindrical body of the vessel, and the effect of welding into stress and strain distribution is carried out. Experimental strains are obtained by using the strain gauges attached to predetermined places and stresses calculated by using Hook’s law in composite materials. The results of the two methods are compared with each other.

X-100 steel is one of the most recently developed materials for production of gas transportation pipelines. This material is severely anisotropic. Smooth and notched round bars with different notch radius and flat notched specimens with different notch radius and notch depth in tension are tested to characterize the failure of this material under quasi-static loading condition.Triaxiality factor that embodies the effect of mean stress and Lode angle are the parameters that affect the failure. Lode angle is a recently introduced parameter in the fracture of ductile materials and contains the effect of third invariant of deviatoric stress tensor. The load-displacement curves and pictures taken by 2 photo camera are used to study the effects of anisotropy, triaxiality factor and Lode angle on the failure of this material. Finally an experimental failure criterion is developed to model the failure of this material. In this failure criterion, strain at fracture initiation is a function of X and TF. Models that take into account the effect of Lode angle, Triaxiality factor and anisotropy in plasticity and damage are the current state of the art in the research of ductile materials.

In this study, the strain rate effect on the bending properties of fiber reinforced composites for three types of polymer composites namely phenolic resin reinforced by woven basalt fibers, woven carbon fibers, and woven basalt/ woven carbon fibers at a total volume fraction of approximately 35% has been determined. Flexural tests have been conducted at low range of strain rates included 0.03 min-1, 0.06 min-1 and 0.09 min-1. Specimens with identical geometry have been used in all the tests. Experimental results showed that the strain rate has a significant effect on the material response in bending. Results showed that, both the flexural modulus and the ultimate flexural strength of the three types of composites are increased with the increasing in the strain rate. Also, the bending properties of composites reinforced with woven carbon fibers are very sensitive to the strain rate during the test.

The problem of crack identification in continuous beam like structures is considered. The cracks’ locations and their depths are identified by employing experimental modal test results performed on the structure. The cracks are modeled using generic elements to include the coupling effects between shear forces and bending moments at the crack section. In the identification procedure eigen- sensitivity analysis of continuous structure is performed by implicit differentiation of structure characteristic equation. The experimentally obtained modal results are exposed to uncertainty including measurement errors, uncertainties in model order determination and etc. Uncertainty may also originate from manufacturing tolerances that are irreducible. To quantify uncertainties, a stochastic model updating is preformed on the structure using multiple sets of modal data. The crack locations and the depths are set to be unknown parameters of the model to be identified using model updating. Stochastic distributions of multiple measurements are determined and via the desired uncertainty propagation method the distribution of model modal predictions is also formed. The model random parameters are determined by matching the distributions of these two sets modal data. The identification process is mainly divided into two adjustment steps of matching the parameters mean value and their related covariance matrix. Here, the uncertainty propagation is performed by the so-called Monte-Carlo simulation for simulating the random processes.

In this paper, based on equations of lateral vibrations of wires, a non contact method for measuring instantaneous tension in a wire is introduced. The lateral vibration of the string is measured using an eddy current transducer and is sent to a computer. This signal is then imported to suitable software for fast Fourier transform (FFT) processing. The first natural frequency of the string is calculated online using FFT plot of the imported signal. This proposed method can be used for measuring tension for both fixed and moving wire with constant velocity, which is a usual case in wire processes. The results show the good agreement with theoretical values and the errors of the method is up to 8% at the worst case. This experimental study shows that this simple and low cost new method can be included in existing non-contact wire measuring tension apparatuses.

In this research work, the effects of natural fibers such as date palm fiber (DF) and jute fiber (JF) on bending properties of polypropylene (PP)/ ethylene–propylene–diene–monomer (EPDM) thermoplastic elastomers are investigated. For this purpose, the date palm and jute fibers at five levels of fiber weight fractions (0, 5, 10, 20 and 30 wt. %) are utilized during composite fabrication. Maleic anhydride grafted to polypropylene (MAPP) is used as coupling agent to increase the interfacial adhesion between the polymer and the fibers. Results show that by adding fiber to the matrix, the bending properties are increased, but elongation at break is decreased.

In this paper effects of fractured sleepers on rail track vibration under moving wheelset have been investigated. Two parallel rails of the track have been modeled as Euler-Bernoulli beams on elastic points as rail pads. Also sleepers have been modeled as visco-elastic Euler-Bernoulli beams. It is assumed that, some sleepers under the rail track have been fractured and modeled by two beams. The wheelset has 5 DOF which are longitudinal, vertical and lateral movements plus roll and axial rotations. To determine normal contact force between wheel and rail, relative position of wheel and rail has been determined at each instant. Using the coordinate of each wheel points in rail coordinate system, the penetration of wheel in rail has been determined. To determine rail-wheel contact forces, Hertzian nonlinear contact theory and Kalker theory have been used. A computer program has been developed that numerically solves the equations of motion of the system for different operating conditions using Runge Kutta Cash-Karp computation method. Using this model the effects of wheelset velocity, wagon weight, number of fractured sleepers and fracture location on rail track vibration have been investigated.

The equal channel angular rolling (ECAR) is one of the severe plastic deformation processes, which can develop a shear deformation into a sheet metal. In this process, internal stresses are created due to the different strain levels experienced in different locations at the same time. The incremental hole drilling method is an effective technique for the evaluation of the through-thickness residual stress distribution in the metal sheets processed by the ECAR. In this work, the residual stresses as the macro stresses have been considered by the help of the incremental method and FEM for numerical calculation of the calibration coefficients. In addition, the FE simulation has been used to investigate the residual stress profile through the thickness. It was observed that the ECARed sample was compressive at the top surface while it was in tension at the bottom surface and the stress profile was not uniform through the material thickness. A comparison between the hole drilling measurements and the FE simulation results showed a good agreement.