SEARCH · Search NASA

Results for “cracking”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44

All sources NASA NTRS DOE OSTI

NASA NTRS1978

Arc termination cracks in Inconel 718 and Incoloy 903

The welding of the nickel base, heat resistant alloys that are used extensively for welded Shuttle engine components revealed solidification cracking characteristics at weld termination points. If not detected and removed, these crater cracks may cause costly component failure. To better understand this characteristic, welding termination techniques were studied and methods developed to eliminate crater cracks. It was determined that weld termination solidification cracking can be eliminated by controlled decrease of welding current, welding voltage, wire feed, and travel speed.

Bayless, E.↗

NASA NTRS1978

A review and assessment of the stress-intensity factors for surface cracks

The stress-intensity factor solutions proposed for a surface crack in a finite plate subjected to uniform tension are reviewed. Fourteen different solutions for the stress-intensity factors are compared. These solutions were obtained over the past 16 years using approximate analytical methods, experimental methods, and engineering estimates. The accuracy is assessed of the various solutions by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material. Fracture of the epoxy material was characterized by a constant value of stress-intensity factor at failure. Thus, the correctness of the various solutions is judged by the variations in the stress-intensity factors at failure. The solutions were ranked in order of minimum standard deviation. The highest ranking solutions correlated 95 percent of data analyzed within + or - 10 percent, whereas the lowest ranking solutions correlated 95 percent of data analyzed within + or - 20 percent. However, some solutions could be applied to all data considered, whereas others are limited with respect to crack shapes and crack sizes that could be analyzed.

Newman, J. C., Jr.↗

NASA NTRS1979

Fatigue crack propagation behaviour of unidirectionally solidified gamma/gamma-prime-delta eutectic alloys

Fatigue crack propagation studies were carried out on unidirectionally solidified gamma/gamma-prime-delta (Ni-Nb-Al) alloys over an aluminum content range of 1.5-2.5% by weight. The variation of Al content of as-grown alloys did not significantly affect the crack growth behavior of these eutectic composites. The results indicate that the addition of Al to the eutectic dramatically improved the FCP behavior. The gamma/gamma-prime-delta alloy exhibited crack growth rates for a given stress intensity range that are an order of magnitude lower than those for the gamma-delta alloy. It is suggested that this difference in FCP behavior can be explained on the basis of stacking fault energy considerations. Extensive delaminations at the crack tip were also revealed, which contributed to the superior fatigue response. Delamination was predominantly intergranular in nature.

Bretz, P. E.↗

NASA NTRS1979

Stress-intensity factors for a wide range of semi-elliptical surface cracks in finite-thickness plates

Surface cracks are among the more common flaws in aircraft and pressure vessel components. Several calculations of stress-intensity factors for semi-elliptical surface cracks subjected to tension have appeared in the literature. However, some of these solutions are in disagreement by 50-100%. In this paper, stress-intensity factors for shallow and deep semi-elliptical surface cracks in plates subjected to tension are presented. To verify the accuracy of the three-dimensional finite-element models employed, convergence was studied by varying the number of degrees of freedom in the models from 1500 to 6900. The 6900 degrees of freedom used here were more than twice the number used in previously reported solutions. Also, the stress-intensity variations in the boundary-layer region at the intersection of the crack with the free surface were investigated.

Raju, I. S.↗

NASA NTRS1979

Fatigue crack growth in fiber reinforced plastics

Fatigue crack growth in fiber composites occurs by such complex modes as to frustrate efforts at developing comprehensive theories and models. Under certain loading conditions and with certain types of reinforcement, simpler modes of fatigue crack growth are observed. These modes are more amenable to modeling efforts, and the fatigue crack growth rate can be predicted in some cases. Thus, a formula for prediction of ligamented mode fatigue crack growth rate is available.

Mandell, J. F.↗

NASA NTRS1980

Multi-Parameter Yield Zone Model for Predicting Spectrum Crack Growth

A systematic technique is presented for modeling crack growth load interaction effects due to spectrum loading. The Multi-Parameter Yield Zone (MPYZ) model accounts for crack growth retardation, acceleration, and underload effects. The load interactions are attributed to the residual stress intensity due to the plastic deformation at the crack tip. Fatigue crack growth was predicted and compared with test data for a variety of spectrum loadings.

Johnson, W. S.↗

NASA NTRS1979

A cracked beam or plate transversely loaded by a stamp

In this paper the problem of an infinite elastic beam or a plate containing a crack is considered. The medium is loaded transversely through a stamp which may be rigid or elastic. The problem is a coupled crack-contact problem which cannot be solved by treating the crack and contact problems separately and by using a superposition technique. First the Green's functions for the general case are obtained. Then the integral equations for a cracked infinite strip loaded by a frictionless stamp are obtained. With the question of fracture in mind, the primary interest in the paper has been in calculating the stress intensity factors. The results are given for a rigid flat stamp with sharp edges and for an elastic curved stamp. The effect of friction at the supports on the stress intensity factors is also studied and a numerical example is given.

Nied, H. F.↗

NASA NTRS1979

Comparison of single crack propagation in lunar analogue glass and the failure strength of rocks

New data of crack propagation in lunar analogue glass provides important input for the construction of deformation maps (maps which delineate the rates and principal means of material deformation under various environmental conditions) applicable to the lunar crust. Comparison of single crack propagation data obtained on flat plates of glass and failure strength data obtained on fine grained rock samples show that single crack propagation velocities are directly related to the failure strength of rocks. The chemical reaction between water and silicon-oxygen bonds at the crack tip seems to be of first order. This greatly simplifies extrapolation to low partial pressures of H2O

Soga, N.↗

NASA NTRS1980

Measurements of mixed-mode crack surface displacements and comparison with theory

The problem of a finite-width tension specimen containing a crack oriented at various angles to the load axis is attacked from experimental and theoretical viewpoints. Displacements of an electro-machined slot, 12.5 mm long and oriented at angles of 0, 15, 30, 45, 60, and 75 deg, are measured using a laser-based in-plane measuring technique. Various width specimens, ranging from a crack-length/width ratio of 0.167 to 0.794, are tested. A boundary-integral equation method is extended to deal with the presence of a sharp crack. Agreement between the two approaches is generally good except near the tips of the cracks.

Sharpe, W. N., Jr.↗

NASA NTRS1980

Crack problems for a rectangular plate and an infinite strip

The general plane problem for an infinite strip containing multiple cracks perpendicular to its boundaries is considered. The problem is reduced to a system of singular integral equations. Two specific problems of practical interest are then studied in detail. The first problem explores the interaction effect of multiple edge cracks in a plate or beam under tension or bending. The second problem is that of a rectangular plate containing an arbitrarily oriented crack in the plane of symmetry. Particular emphasis is placed on the problem of a plate containing an edge crack and subjected to concentrated forces.

Civelek, M. B.↗

NASA NTRS1979

A review and assessment of the stress-intensity factors for surface cracks

The stress-intensity factor solutions proposed for a surface crack in a finite plate subjected to uniform tension are reviewed. Fourteen different solutions obtained over the past 16 years using approximate analytical methods, experimental methods, and engineering estimates are compared. The accuracy of the various solutions is assessed by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material. Fracture of the epoxy material was characterized by a constant value of stress-intensity factor as failure. Thus, the correctness of various solutions is judged by the variations in the stress-intensity factors at failure. The solutions were ranked in order of minimum standard deviation. The highest ranking solutions correlated 95% of data analyzed within + or - 10% whereas the lowest ranking solutions correlated 95% of data analyzed within + or - 20%. Some solutions could be applied to all data considered, whereas others were limited with respect to crack shapes and crack sizes that could be analyzed.

Newman, J. C., Jr.↗

NASA NTRS1981

Dynamic crack propagation and arrest in orthotropic DCB fiber composite specimens

An orthotropic double cantilever beam (DCB) model is used to study dynamic crack propagation and arrest in 90 deg unidirectional Hercules AS/3501-6 graphite fiber epoxy composites. The dynamic fracture toughness of the composite is determined from tests performed on the long-strip specimen and DCB crack arrest experiments are conducted. By using the dynamic fracture toughness in a finite-difference solution of the DCB governing partial differential equations, a numerical solution of the crack propagation and arrest events is computed. Excellent agreement between the experimental and numerical crack arrest results are obtained.

Williams, J. H., Jr.↗

NASA NTRS1981

Analysis of crack propagation as an energy absorption mechanism in metal matrix composites

The crack initiation and crack propagation capability was extended to the previously developed generalized plane strain, finite element micromechanics analysis. Also, an axisymmetric analysis was developed, which contains all of the general features of the plane analysis, including elastoplastic material behavior, temperature-dependent material properties, and crack propagation. These analyses were used to generate various example problems demonstrating the inelastic response of, and crack initiation and propagation in, a boron/aluminum composite.

Adams, D. F.↗

NASA NTRS1982

The crack and wedging problem for an orthotropic strip

The plane elasticity problem for an orthotropic strip containing a crack parallel to its boundaries is considered. The problem is formulated under general mixed mode loading conditions. The stress intensity factors depend on two dimensionless orthotropic constants only. For the crack problem the results are given for a single crack and two collinear cracks. The calculated results show that of the two orthotropic constants the influence of the stiffness ratio on the stress intensity factors is much more significant than that of the shear parameter. The problem of loading the strip by a rigid rectangular lengths continuous contact is maintained along the wedge strip interface; at a certain critical wedge length the separation starts at the midsection of the wedge, and the length of the separation zone increases rapidly with increasing wedge length.

Cinar, A.↗

NASA NTRS1981

Cracked shells under skew-symmetric loading

The general problem of a shell containing a through crack in one of the principal planes of curvature and under general skew-symmetric loading is considered. By employing a Reissner type shell theory which takes into account the effect of transverse shear strains, all boundary conditions on the crack surfaces are satisfied separately. Consequently, unlike those obtained from the classical shell theory, the angular distributions of the stress components around the crack tips are shown to be identical to the distributions obtained from the plane and anti-plane elasticity solutions. Results are given for axially and circumferentially cracked cylindrical shells, spherical shells, and toroidal shells under uniform in-plane shearing, out of plane shearing, and torsion. The problem is formulated for specially orthostropic materials, therefore, the effect of orthotropy on the results is also studied.

Delale, F.↗

NASA NTRS1981

Multi-parameter yield zone model for predicting spectrum crack growth

A phenomenological load interaction model referred to as the Multi-Parameter Yield Zone model is presented which accounts for crack growth retardation caused by previous overloads, acceleration due to current overloads, and underload effects. In the present model, load interaction effects are calculated utilizing a residual stress intensity concept. Crack growth retardation and acceleration are accounted for by decreasing or increasing, respectively, the effective stress ratio used in a modified Forman's (1967) crack growth equation. Results of spectrum crack growth predictions for 2219-T851 aluminum are presented.

Johnson, W. S.↗

NASA NTRS1982

Application of the line-spring model to a cylindrical shell containing a circumferential or axial part-through crack

The line-spring model developed by Rice and Levy (1972) is used to obtain an approximate solution for a cylindrical shell containing a part-through surface crack. A Reissner type theory is used to account for the effects of the transverse shear deformations, and the stress intensity factor at the deepest penetration point of the crack is tabulated for bending and membrane loading by varying three-dimensionless length parameters of the problem formed from the shell radius, the shell thickness, the crack length, and the crack depth. The upper bounds of the stress intensity factors are provided, and qualitatively the line-spring model gives the expected results in comparison with elasticity solutions.

Delale, F.↗

NASA NTRS1982

Shaft vibrations in turbomachinery excited by cracks

During the past years the dynamic behavior of rotors with cracks has been investigated mainly theoretically. This paper deals with the comparison of analytical and experimental results of the dynamics of a rotor with an artificial crack. The experimental results verify the crack model used in the analysis. They show the general possibility to determine a crack by extended vibration control.

Grabowski, B.↗