Khosrow Zarrabi

A Novel and Simple Approach for Predicting Creep Life Based on Tertiary Creep Behavior

The creep of materials is a research topic of major significance in the life assessment and design of many modern engineering components of advanced technology such as power generation plant, chemical plant, gas turbines, jet engines, spacecrafts, and components made of plastics and polymers. To predict the creep life of such components, one necessary ingredient is a creep damage model. The current creep damage models are either too cumbersome to be readily employed and/or not sufficiently accurate for practical applications. This paper describes a new multiaxial creep damage model that alleviates the major shortcomings of the existing models. Yet it is relatively simple and accurate and is readily applicable to industrial cases.

Estimation of boiler tube life in presence of corrosion and erosion processes

Abstract A simple method is developed to estimate the life of boiler tubes of fossil-fuel power plants. The method is applicable when the dominant mode of failure is creep rupture and/or plastic collapse followed by fracture in the presence of tube thickness loss caused by corrosion and/or erosion processes. The method uses both International Organization for Standardization (ISO) and θ-projection rupture data and does not require creep stress index as an input. It is concluded that the θ-projection rupture data produce less conservative estimates of the life of boiler tubes than those obtained using ISO data.

A comparison of several boiler tube life prediction methods

Abstract Four methods for predicting the life of boiler tubes are compared. The methods are the UNSW method (developed by the author), the CEGB-OH method (developed by the Central Electricity Generating Board in the United Kingdom and reported in an Ontario Hydro report), the CTS-OH method (developed by the Central Thermal Services of Ontario Hydro in Canada), and the RD-OH method (developed by the Research Division of Ontario Hydro). It was demonstrated that the UNSW method that has the option of using the θ-projection rupture data predicts the longest tube lives. Other advantages of the UNSW method are that it does not require the creep stress index as an input, which can be a major source of error; and that it is applicable to boiler tubes that operate either within or below the creep range whereas the other methods are applicable to tubes that operate within the creep range only.

Non-contacting creep strain determination at 550 °C

The digital speckle correlation technique (DSCT) is a non-contacting and whole field displacement/strain measurement system that has been successfully applied to a variety of applications. The technique is based on correlating the speckle surface of the object before and after deformation. It is best suited for flat surfaces. Creep deformation may, however, cause decorrelation of the speckle surface. The ability of DSCT to measure creep displacement/strain fields at 550 °C using 2.25%Cr 1%Mo steel specimens was evaluated. The specimens were cylindrical so that the effect of a non-flat surface was also included. Results show that DSCT can measure creep displacement and strain fields under laboratory conditions with less than 5% error. Further research and development work are required to assess the applicability of DSCT for creep displacement/strain measurements under field conditions.

Stretch‐dependent changes in surface profiles of the human crystalline lens during accommodation: A finite element study

A non‐linear isotropic finite element (FE) model of a 29‐year‐old human crystalline lens was constructed to study the effects of various geometrical parameters on lens accommodation.

A finite volume element formulation for solution of elastic axisymmetric pressurized components

The authors have previously proposed the equivalent volume hypothesis (EVH) as part of integrity assessment of boiler tubes subjected to external erosion/corrosion. Currently, research is in progress at The University of New South Wales to develop and verify the EVH for tubes subjected to internal corrosion. This paper describes the formulation, verification and application of an axisymmetric and elastic finite volume element to internally corroded tubes. The initial computed results indicate that EVH is valid for these tubes.

Creep life assessments of defect-free components under uniform load and temperature

Abstract A robust (simple and conservative) method for determining the creep life of a defect-free component subjected to uniform load and temperature is described. This method has been specifically developed for the components containing stress concentrators. It is called the UNSW-LIFE2 method and requires only the elastic stresses, the uniaxial creep rupture data and the steady-state creep solution for the plain component excluding stress concentrators; the latter is readily available from literature and is normally simple to calculate.

A Mesoscopic Damage Model for Predicting the Plastic-Creep Life of Welded Joints Subjected to Quasi-Static Loading

The integrity and life assessment of welded joints operating at high temperatures and subjected to non-linear damage mechanisms such as plasticity and creep are complex engineering problems and currently the subject of intensive research activities. This paper gauges the accuracy of a model that takes into account creep and plasticity deformation proposed by Zarrabi et al. to a butt welded thick tube. It is shown that the proposed model can predict the life of this welded joint with an error of 1%. Currently the model is being extended to include fatigue deformation.Copyright

A Novel and Simple Approach for Predicting Creep Life Based on Tertiary Creep Behaviour

The creep of materials is a research topic of major significance in the life assessment and design of many modern engineering components of advance technology such as: power generation plant, chemical plant, gas turbines, jet engines, spacecrafts, components made of plastics and polymers, etc. To predict the creep life of such components, one necessary ingredient is a creep damage model. The current creep damage models are either too cumbersome to be readily employed and/or not sufficiently accurate for practical applications. This paper describes a new multiaxial creep damage model that alleviates the major shortcomings of the existing models yet it is simple and accurate enough to be readily applicable to industrial cases.Copyright

Primary stress in scarred boiler tubes

Abstract A P ∗ parameter is described that can be used to determine the primary stress in a scarred boiler tube. The scar may be due to localized erosion or corrosion. This primary stress can then be used as one of the ingredients for estimating the tube life.