Fatigue-crack-growth-rate tests were conducted on compact tension specimens made of 7050-T7451 aluminum alloy and 9310 steel. Compact tension specimens were tested over a wide range of load ratios (0.1 less than, or equal to R less than, or equal to 0.9) to generate crack-growth-rate data from threshold to near fracture. Three methods were used to generate near threshold data. A crack-closure analysis was performed on both materials using the FASTRAN crack-closure model. The crack-growth-rate data for each material correlated very well and each collapsed onto a nearly unique curve in the low- and mid-rate regimes using the strip-yield model in the FASTRAN life-prediction code. For the 7050 alloy, a constraint factor of α = 1.8 was required, while for the 9310 steel α = 2.5 worked very well in correlating the test data over a very wide range in R values and rates from threshold to near fracture.

Surface-crack configurations are among the most important crack problems in the aerospace industry. The residual strength of a surface-cracked component is complicated by three-dimensional variation of the stress-intensity factor around the crack front and plastic deformations, which vary from plane stress at the free boundary, to nearly plane-strain behavior in the interior. In 1973, a two-parameter fracture criterion (TPFC) was developed to analyze fracture behavior of surface-crack configurations. Estimates were made around the crack front for fracture initiation—the critical parametric angle. Recently, NASA developed the Tool for Analysis of Surface Cracks (TASC) software that predicts critical location. This thesis is the application of the TPFC with the TASC critical angles using an equation developed from the TASC software. The TPFC was applied to three materials: a brittle titanium alloy, a ductile titanium alloy, and a ductile 301 stainless steel. The TPFC with the TASC critical angles correlated fracture behaviors well.

Fatigue and crack-growth tests were conducted on 7050-T7451 aluminum alloy under a wide range of loading conditions. Crack-growth tests were conducted on compact, C(T), specimens under constant-amplitude loading, single-spike overloads, and a simulated aircraft spectrum loading. Fatigue tests were also conducted on single-edge-notch bend, SEN(B), specimens under constant-amplitude loading and three aircraft load spectra. The FASTRAN, life-prediction code, was used to make crack-growth predictions on the C(T) specimens; and to make fatigue-life calculations using a 12-micrometer initial flaw size at the center of the edge-notch on the SEN(B) specimens. The predictions agreed fairly well with most of the tests, except the model was unconservative on the single-spike overload tests and the severe spectrum Mini-TWIST+ Level 1 tests. The discrepancy was suspected to be caused by a low constraint factor and/or crack paths meandering around overload plastic zones. A roughness- and plasticity-induced crack-closure model would be needed to improve the model.

This thesis presents a numerical formulation which incorporates the effects of joints, cracks, and fractures into a mathematical mode used to in an existing finite element code. Two separate crack definitions were incorporated, one involving a discrete crack model, and the other a continuum approach defining a new material with regularly spaced joints. Several examples are also presented demonstrating the use of this capability.

Timber is becoming an increasingly popular construction material particularly due to its great environmental properties. Just alone around Linnaeus University in Växjö city, dozens of multistory buildings in timber have risen. As the demand for more timber construction is becoming popular, the understanding of timber design must evolve at the same pace. One of the most important parts of timber construction are the connections that hold everything together. One variable that is used to design connections is the embedment behavior. This thesis examined how the embedment behavior of a steel dowel in wood is influenced by moisture content, assembly history, and artificial cracks. In this case the assembly history refers to if the drilling and insertion of the steel dowel was done before or after drying or wetting the specimen. The idea behind the artificial crack was to achieve something similar to a real crack where the crack was created with a precision saw to separate the fibers parallel to the grain. The embedment behavior was studied by means of embedment strength, elastic- and plastic embedment stiffness. In total, 140 embedment experiments were conducted to study the embedment behavior of the dowel in wood. All embedment experiments were carried out parallel to the fiber direction using two species of wood, spruce and birch. Each experimental series had its own attributes to allow a comparison of how the embedment behavior is influenced by moisture content, assembly history, and artificial cracks. The data from the experiments was then used as input to create computer models where the beam on foundation modeling approach was used in conjunction with the finite element computer program Abaqus. A timber-steel-timber connection was modeled to study the influence of the side timber member thickness on the overall strength. The results of the experiments showed that the moisture content and the assembly history can potentially affect the embedment strength and the elastic, and the plastic embedment stiffness. The series that studied the influence of artificial cracks showed that mostly the embedment strength and elastic embedment stiffness are affected by artificial cracks. The numerical simulations indicated that the moisture profile from the experimental data had less influence on the strength for thicker timber side members than it did on thinner. In general, this thesis provides new insights and a better understanding of how the embedment behavior is influenced by moisture content, assembly history, and artificial cracks.

Majority of the swimming facilities in Sweden are facing some form of renovation or total substitution. The report analyses cracks in two different public bath facilities namely Eriksdalsbadet and Enskedehallen. The text also discusses different solution strategies for cracks in concrete. The aim with this thesis is to discuss how facility managers can extend the service life of these facilities by taking measures against the crack damages. Since renovation can be expensive, it is important to study cracks early on when they appear. This thesis also emphasizes on how important it is to add resources for preventing cracks, already during casting. Resources should also be added for maintaining the basins, managing repair methods for all types of cracking problems. This thesis is more of a generalized study for cracks in concrete, however it concludes with taking a more specific approach by discussing the problems in swimming basins. Causes of cracks, different types of cracks and evolution of cracks are studied and discussed with emphasis on the structural damages that can occur. With pictures taken and analyzed from the two facilities and a visitation with a experienced concrete investigator from CBI, this thesis concludes with a decision to immediately take repair actions against cracks that are shown in the report. The report discusses two perspectives, one where the authors of the thesis discusses solutions derived from information given in the report, and the other perspective is derived from guided inspection with consultant from CBI. / Neris projektet

Transverse ply cracking often leads to the loss of stiffness and reduction in thermal expansion coefficients. This paper presents the thermoelastic degradation of general cross-ply laminates, containing transverse ply cracks, subjected to biaxial extension, bending and thermal loading. The stress and displacement fields are calculated by using the state space equation method [Zhang D, Ye JQ, Sheng HY. Free-edge and ply cracking effect in cross-ply laminated composites under uniform extension and thermal loading. Compos Struct [in press].]. By this approach, a laminated plate may be composed of an arbitrary number of orthotropic layers, each of which may have different material properties and thickness. The method takes into account all independent material constants and guarantees continuous fields of all interlaminar stresses across interfaces between material layers. After introducing the concept of the effective thermoelastic properties of a laminate, the degradations of axial elastic moduli, Poisson¿s ratios, thermal expansion coefficients and flexural moduli are predicted and compared with numerical results from other methods or available test results. It is found that the theory provides good predictions of the stiffness degradation in both symmetric and antisymmetric cross-ply laminates. The predictions of stiffness reduction in nonsymmetric cross-ply laminates can be used as benchmark test for other methods.

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