Engineering topics

Forman, Royce

Publications and source records attributed to Forman, Royce.

7 records

NASA NTRS2010

Experimental Evaluation of Fatigue Crack Initiation from Corroded Hemispherical Notches in Aerospace Structural Materials

A test program was developed and executed to evaluate the influence of corroded hemispherical notches on the fatigue crack initiation and propagation in aluminum 7075-T7351, 4340 steel, and D6AC steel. Surface enhancements such as shot peening and laser shock peening were also incorporated as part of the test effort with the intent of improving fatigue performance. In addition to the testing, fracture mechanics and endurance limit based analysis methods were evaluated to characterize the results with the objective of challenging typical assumptions used in modeling fatigue cracks from corrosion pits. The results specifically demonstrate that the aluminum and steel alloys behave differently with respect to fatigue crack initiation from hemispherical corrosion pits. The aluminum test results were bounded by the fracture mechanics and endurance limit models while exhibiting a general insensitivity to the residual stress field generated by shot peening. The steel specimens were better characterized by the endurance limit fatigue properties and did exhibit sensitivities to residual stresses from the shot peening and laser shock peening

Garcia, Daniel B.↗

NASA NTRS2007

Numerical Strip-Yield Calculation of CTOD

Many existing methods to calculate CTOD can be costly and complicated, or apply only to particular configurations. A new numerical method for calculating CTOD was investigated. NASGRO's Boundary Element module NASBEM was adapted to calculate displacements at any point on the crack. Demonstrated for a number of crack configurations: a) finite and infinite domains; b) center and edge cracks; and c) complex cases with several cracks and holes. Great accuracy at minimal computational cost.

Beek, Joachim↗

NASA NTRS2007

Numerical Strip-Yield Calculation of CTOD and CTOA

A recently developed numerical method based on the strip yield analysis approach was used to calculate the Crack Tip Opening Displacement (CTOD) and Crack Tip Opening Angle (CTOA) for a number of complex crack configurations of practical interest. This method is an adaptation of the dislocation-density based boundary element method. In this Boundary Element approach, crack-face opening displacements are obtained at any point on a crack using a series of definite integrals evaluated exactly in closed form for a variety of crack geometries, including infinite or finite extent, with arbitrarily applied loading conditions.

Beek, Joachim↗

NASA NTRS2006

Effects of Laser and Shot Peening on Fatigue Crack Growth in Friction Stir Welds

The effects of laser, and shot peening on the fatigue life of Friction Stir Welds (FSW) have been investigated. The surface roughness resulting from various peening techniques was assessed, and the fracture surfaces microstructure was characterized. Laser peening resulted in an increase in fatigue life approximately 60%, while shot peening resulted in 10% increase when compared to the unpeened material. The surface roughness of shot peening was significantly higher compared to the base material, while specimens processed with laser peening were relatively smooth.

Hatamleh, Omar↗

NASA NTRS2006

Strip Yield Model Numerical Application to Different Geometries and Loading Conditions

A new numerical method based on the strip-yield analysis approach was developed for calculating the Crack Tip Opening Displacement (CTOD). This approach can be applied for different crack configurations having infinite and finite geometries, and arbitrary applied loading conditions. The new technique adapts the boundary element / dislocation density method to obtain crack-face opening displacements at any point on a crack, and succeeds by obtaining requisite values as a series of definite integrals, the functional parts of each being evaluated exactly in a closed form.

Hatamleh, Omar↗

NASA NTRS2006

Laser Peening and Shot Peening Effects on Fatigue Life and Surface Roughness of Friction Stir Welded 7075-T7351 Aluminum

The effects of laser peening, shot peening, and a combination of both on the fatigue life of Friction Stir Welds (FSW) was investigated. The fatigue samples consisted of dog bone specimens and the loading was applied in a direction perpendicular to the weld direction. Several laser peening conditions with different intensities, durations, and peening order were tested to obtain the optimum peening parameters. The surface roughness resulting from various peening techniques was assessed and characterized. The results indicate a significant increase in fatigue life using laser peening compared to shot peened versus their native welded specimens.

Hatamleh, Omar↗

NASA NTRS2004

NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.

Forman, Royce↗