TMS 2009 138th Annual Meeting & Exhibition

February 15-19, 2009

The conference held in San Francisco, CA was attended by:

Graduate Students: Brendan Chantelle, Anastasios Gavras, Christopher Lammi, Jodi Lowell, Kimon Symeonidis, Chang-Kai (Lance) Wu

Professors: Diran Apelian, Diana Lados, Makhlouf Makhlouf, Richard Sisson, Jr.

Post Doc: Animesh Mandal

Papers presented:

Predicting Residual Stresses Caused by Heat Treating Cast Aluminum Alloy Components
Microstructure and Mechanical Properties of Cast Hypereutectic Al-Si Alloys with High Magnesium Content
A comparison of gas and low pressure carburization of 9310 and 8620 steels - a numerical simulation study
Modeling of Residual Stress Fields in Structural Materials: Computational, Mechanical, and Metallurgical Approaches
Effects of Processing Residual Stresses on Fatigue Crack Growth Behavior of Structural Materials
Fatigue Crack Growth Behavior of Long and Small Cracks in Structural Materials

Predicting Residual Stresses Caused by Heat Treating Cast Aluminum Alloy Components

Presented at the Symposium Shape Casting: Third International Symposium

Authors:

Chang-Kai Wu, Makhlouf M. Makhlouf

Abstract

Abstract Scope A mathematical model that enables the prediction of the effects of heat treatment on cast aluminum alloy components has been developed. The model uses the commercial software ABAQUS to predict residual stresses in heat treated components. An extensive database has been developed for A356 aluminum alloy and includes the mechanical, physical, and thermal properties of the alloy as functions of temperature. In addition, boundary conditions ? in the form of heat transfer coefficients for each of the heat treatment steps ? have been obtained from measurements performed with a specially designed quenching system. The database and boundary conditions were used to predict the response of a typical A356 cast component to a standard commercial heat treating cycle and the model predictions were found to be in good agreement with their measured counterparts.

A comparison of gas and low pressure carburization of 9310 and 8620 steels - a numerical simulation study

Authors:

Gang Wang, Mohammed Maniruzzaman and Richard D. Sisson, Jr.

Abstract

A comparative study of gas caburization and low pressure carburization processes has been performed using CHTE's numerical simulation software - CarbTool. CarbTool is a 1-D carbon diffusion model developed based on the thermodynamics and kinetics of the carburization process. The model is capable of simulating the complex boost-diffuse processes used in the industry. The output of CarbTool is the carbon concentration distribution inside the part. Two steels-9310 and 8620 are investigated in this study. The quenching process of carburized rods is simulated using DANTE/ABAQUS FEM software. Results are compared in terms of carbon profile, microstructures and residual stresses.

Microstructure and Mechanical Properties of Cast Hypereutectic Al-Si Alloys with High Magnesium Content

Authors:

A. Mandal and M.M. Makhlouf

Abstract

Magnesium in excess of the quantities typically found in commercial hypereutectic Al-Si alloys can produce alloys with enhanced microstructure and attractive mechanical properties. With addition of Mg to hypereutectic Al-Si alloys, the primary silicon phase is suppressed and is replaced with a fine dispersion of small Si particles. However, an abundance of large Mg2Si particles with Chinese script morphology also forms in the microstructure and unfavorably influences the tensile properties of the alloy. Efforts were made to overcome the negative effects of these particles by manipulating their size and morphology. Several additives were made to a hypereutectic Al-Si-Mg alloy and their effect on the cast alloy was determined. The alloy treated with Misch Metal and Strontium showed promising results. The Mg2Si particles that formed in castings made from this alloy were very small and almost spherical; and the room temperature tensile and yield strengths of cast bars were remarkably high.

Modeling of Residual Stress Fields in Structural Materials: Computational, Mechanical, and Metallurgical Approaches

Authors:

Christopher J. Lammi and Diana A. Lados

Abstract:

Adjusting/controlling macro residual stress fields while preserving a desired microstructure is often a challenging proposition. A novel mechanical/geometrical technique able to generate controlled residual stress fields was developed. The method is based on a "plug-and-hole" approach and was used to produce set residual stress magnitudes and distributions in rectangular coupons and compact tension specimens. Residual stress fields created through this method were first modeled computationally using ANSYS software and then reproduced using metallurgical means by adjusting the processing conditions. Long fatigue crack growth data for low and high residual stress conditions were generated and compared. High residual stresses were introduced in the testing samples using both the mechanical/"plug-and-hole" method and metallurgical/processing techniques. Effects of residual stress on crack growth thresholds and fracture toughness are presented and discussed. The developed method is proposed to facilitate the acquisition and analysis of fatigue crack growth data in the presence of residual stress.

Effects of Processing Residual Stresses on Fatigue Crack Growth Behavior of Structural Materials

Authors:

Christopher J. Lammi and Diana A. Lados

Abstract:

Fatigue crack growth mechanisms of long cracks through fields with high and low residual stresses were investigated for various structural materials commonly used in transportation applications. Macro residual stresses were introduced within each material first by processing methods, and then replicated in both magnitude and distribution, through original mechanical/geometrical techniques. Residual stresses were measured/paired using microstructure-tailored X-ray diffraction techniques. Compact tension specimens were fatigue crack growth tested at room temperature and stress ratio, R=0.1. Residual stress corrections were done using the Restoring Force Model, and the results were compared to those generated by a real-time compliance correction technique. Qualitative and quantitative effects of residual stress on fatigue crack growth characteristics, such as fatigue crack growth threshold and fracture toughness, will be presented and discussed for each material/class. Recommendations are given for fatigue crack growth data collection and interpretation to facilitate consistent and accurate design in the presence of residual stress.

Fatigue Crack Growth Behavior of Long and Small Cracks in Structural Materials

Authors:

Anastasios G. Gavras and Diana A. Lados

Abstract

Fatigue crack propagation of long and small cracks was investigated for various structural materials. For most materials, two microstructures were prepared and tested. Low residual stress was ensured during processing to shed light on microstructural effects on crack growth. Compact tension and single edge tension specimens were fatigue crack growth tested at room temperature and stress ratio, R=0.1. Microstructure related mechanisms were used to explain the near-threshold behavior and crack growth responses in Regions II and III for each material/microstructure. Threshold behavior of long cracks is attributed to closure-dependent mechanisms. In Regions II and III, the changes in crack growth mechanisms were explained by the extent of the plastic zone ahead of the crack tip. Threshold behavior of small cracks is explained through closure-independent mechanisms, specifically through the barrier effects of characteristic features specific to each material/microstructure. Recommendations for integrating materials knowledge in structural design for fatigue performance are given.

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