Bahram Farahmand - Academia.edu (original) (raw)
Uploads
Papers by Bahram Farahmand
Engineering Fracture Mechanics, 2008
The safe-life assessment of components requires information such as the plane stress (K c), plane... more The safe-life assessment of components requires information such as the plane stress (K c), plane strain (K Ic), partthrough fracture toughness (K Ie), and the fatigue crack growth rate properties. A proposed parametric/theoretical approach, based on an extended Griffith theory is used to derive fracture toughness properties and generate fatigue crack growth rate data for a range of alloys. The simplicity of the concept is based on the use of basic, and in most cases available, uniaxial stress-strain material properties data to derive material fracture toughness values. However since the methodology is in part based on an empirical relationship a wide ranging validation with actual data is required. This paper uses steel, aluminum and titanium based alloys from a pedigree database to quantify material properties sensitivity to the predictions for K Ic and K c and the subsequent estimation of DK th threshold and the Paris constants, C and n values. A sensitivity analysis using experimental scatter bounds show the range of da/dN predictions can be achieved. It is found K Ic / DK th ratios designated as a has a range of 5-25 irrespective of tensile ductility, e f , and is insensitive to it. The value of DK th for all the alloys considered was found to be proportional to the final elongation, e f , and an empirical relationship describing DK th as a function of e f was established. Furthermore it is suggested that, with the knowledge of appropriate tensile properties and the estimated range of K Ic /DK th ratios for the different alloys applying this method could be an appropriate tool that can be used to conservatively predict fracture and fatigue in similar alloy categories. Thus helping to reduce costs and optimize the number of experimental tests needed for alloy characterizations.
Materials & Design, 2011
Theoretical and Applied Fracture Mechanics, 2009
Key Engineering Materials, 2013
Evaluating fracture and fatigue life properties of structural components involves tests that are ... more Evaluating fracture and fatigue life properties of structural components involves tests that are costly and time consuming. To estimate total life of engineering parts, high cycle fatigue data (S-N) for the material under study is needed. In many cases the S-N data is not available to the analyst and both the time and budget required for testing prevent engineers to meet the deadline imposed on the program. An analytical combined Progressive Damage and Fracture Mechanics based approach is proposed that estimates the S-N data for components that have stress concentrations. The proposed methodology starts from a full engineering tensile stress-strain curve of the material under study and ends up with the estimation of fracture toughness, fatigue crack growth and fatigue S-N curves.
48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2007
Engineering Fracture Mechanics, 1980
ABSTRACT
Engineering Fracture Mechanics, 2008
The safe-life assessment of components requires information such as the plane stress (K c), plane... more The safe-life assessment of components requires information such as the plane stress (K c), plane strain (K Ic), partthrough fracture toughness (K Ie), and the fatigue crack growth rate properties. A proposed parametric/theoretical approach, based on an extended Griffith theory is used to derive fracture toughness properties and generate fatigue crack growth rate data for a range of alloys. The simplicity of the concept is based on the use of basic, and in most cases available, uniaxial stress-strain material properties data to derive material fracture toughness values. However since the methodology is in part based on an empirical relationship a wide ranging validation with actual data is required. This paper uses steel, aluminum and titanium based alloys from a pedigree database to quantify material properties sensitivity to the predictions for K Ic and K c and the subsequent estimation of DK th threshold and the Paris constants, C and n values. A sensitivity analysis using experimental scatter bounds show the range of da/dN predictions can be achieved. It is found K Ic / DK th ratios designated as a has a range of 5-25 irrespective of tensile ductility, e f , and is insensitive to it. The value of DK th for all the alloys considered was found to be proportional to the final elongation, e f , and an empirical relationship describing DK th as a function of e f was established. Furthermore it is suggested that, with the knowledge of appropriate tensile properties and the estimated range of K Ic /DK th ratios for the different alloys applying this method could be an appropriate tool that can be used to conservatively predict fracture and fatigue in similar alloy categories. Thus helping to reduce costs and optimize the number of experimental tests needed for alloy characterizations.
Materials & Design, 2011
Theoretical and Applied Fracture Mechanics, 2009
Key Engineering Materials, 2013
Evaluating fracture and fatigue life properties of structural components involves tests that are ... more Evaluating fracture and fatigue life properties of structural components involves tests that are costly and time consuming. To estimate total life of engineering parts, high cycle fatigue data (S-N) for the material under study is needed. In many cases the S-N data is not available to the analyst and both the time and budget required for testing prevent engineers to meet the deadline imposed on the program. An analytical combined Progressive Damage and Fracture Mechanics based approach is proposed that estimates the S-N data for components that have stress concentrations. The proposed methodology starts from a full engineering tensile stress-strain curve of the material under study and ends up with the estimation of fracture toughness, fatigue crack growth and fatigue S-N curves.
48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2007
Engineering Fracture Mechanics, 1980
ABSTRACT