Crack closure

About: Crack closure is a research topic. Over the lifetime, 28157 publications have been published within this topic receiving 588158 citations.

Fracture Initiation Due to Asymmetric Impact Loading of an Edge Cracked Plate

Abstract: The two-dimensional elastodynamic problem of a semi-infinite plate containing an edge crack is considered. A normal velocity is suddenly imposed on the boundary of the plate on one side of the edge crack. A combination of transient mode I and mode II deformation fields is induced near the crack tip. The corresponding stress intensity factor histories are determined exactly by linear superposition of several more readily obtainable stress wave propagation solutions. The stress intensity factor histories are determined for the time interval from initial loading until the first wave scattered at the crack tip is reflected at the plate edge and returns to the crack tip

Small-crack effects in high-strength aluminum alloys

Abstract: The National Aeronautics and Space Administration and the Chinese Aeronautical Establishment participated in a Fatigue and Fracture Mechanics Cooperative Program. The program objectives were to identify and characterize crack initiation and growth of small cracks (10 microns to 2 mm long) in commonly used US and PRC aluminum alloys, to improve fracture mechanics analyses of surface- and corner-crack configurations, and to develop improved life-prediction methods. Fatigue and small-crack tests were performed on single-edgenotch tension (SENT) specimens and large-crack tests were conducted on center-crack tension specimens for constant-amplitude (stress ratios of -1, 0, and 0.5) and Mini-TWIST spectrum loading. The plastic replica method was used to monitor the initiation and growth of small fatigue cracks at the semicircular notch. Crack growth results from each laboratory on 7075-T6 bare and LC9cs clad aluminum alloys agreed well and showed that fatigue life was mostly crack propagation from a material defect (inclusion particles or void) or from the cladding layer. Finite-element and weight-function methods were used to determine stress intensity factors for surface and corner cracks in the SENT specimens. Equations were then developed and used in a crack growth and crack-closure model to correlate small- and large-crack data and to make life predictions for various load histories. The cooperative program produced useful experimental data and efficient analysis methods for improving life predictions. The results should ultimately improve aircraft structural reliability and safety.

R‐Curve Behavior and Crack‐Closure Stresses in Barium Titanate and (Mg,Y)‐PSZ Ceramics

Abstract: R-curves, process zones, and shielding stresses of barium titanate (BaTiO3) and partially stabilized zirconia (PSZ) have been studied using compact-tension (CT) specimens. BaTiO3 and PSZ exhibited pronounced R-curves that rose over similar crack lengths and showed steady-state toughnesses of 0.7 and 6.4 MPa·m1/2, respectively. Both steady-state toughnesses were ∼80% larger than the initial fracture toughnesses. Ferroelastic domain switching was the main toughening mechanism in BaTiO3, whereas, in PSZ, transformation toughening was the main toughening mechanism. The crack process zone and crack-opening-displacement (COD) profile of each material was studied in detail using atomic force microscopy. Crack-closure-stress distributions were extracted from the COD profiles, using weight-function methods. The resulting stress profiles indicated that compressive residual stresses of 40 MPa in BaTiO3 and 400 MPa in PSZ acted in a limited region behind the crack tip. In the PSZ, crack bridging seemed to be a competing mechanism to transformation toughening.

Cracking analysis based on slip and bond stresses

Abstract: A theory for crack formation in reinforced concrete elements based on an analysis of slip, bond stresses, and steel stresses is presented. The problem is treated as an initial value problem both for initial crack formation when the cracks are independent, and for stabilized crack formation when the zones of bond stresses reach each other. Simple rules for analysis are presented for initial crack formation derived from the analytical solution of the mathematical model using homogeneous initial values. As an application, the spalling crack width control of a prestresesd pretensioned bridge girder is estimated. Numerical analysis is presented for stabilized crack formation. Tension stiffening is analyzed as a result of the interface behavior.

Quantification of constraint effects in elastic-plastic crack front fields

Abstract: In-plane and out-of-plane constraint effects on crack tip stress fields under both small-scale and large-scale yielding conditions are studied by means of three-dimensional numerical analyses of boundary layer models and of finite size specimens, M(T) and SE(B), respectively. It is shown that the ratio of the plastic zone size over the panel thickness, rpt, plays a key role in formation of the crack-tip fields, particularly the outof-plane stress components. For a vanishingly small plastic zone around the crack tip the stress fields are dominated by the plane strain solution. With increase of the applied loads, i.e. increasing the plastic zone size, the stress fields develop towards the plane stress state. Characterization of “constraint effects” in terms of Q-stress is investigated. The “second term” in the near tip stress field, which is defined as the difference between the full three-dimensional stress fields and the plane strain reference solution, appears to depend on the distance to the tip and to the free surface of the specimen. Hence, the whole three-dimensional crack front fields cannot be correctly described by a two-parameter formulation as the load increases. However, a unique linear relationship between Q and the hydrostatic stress was found in all three-dimensional crack front fields.