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Crack propagation and branching are modeled using nonlocal peridynamic theory. One major advantage of this nonlocal theory based analysis tool is the unifying approach towards material behavior modeling- irrespective of whether the crack is formed in the material or not. No separate damage law is needed for crack initiation and propagation. This theory overcomes the weaknesses of existing continuum mechanics based numerical tools (e.g. FEM, XFEM etc.) for identifying fracture modes and does not require any simplifying assumptions. Cracks grow autonomously and not necessarily along a prescribed path. However, in some special situations such as in case of ductile fracture, the damage evolution and failure depend on parameters characterizing the local stress state instead of peridynamic damage modeling technique developed for brittle fracture. For brittle fracture modeling the bond is simply broken when the failure criterion is satisfied. This simulation helps us to design more reliable modeling tool for crack propagation and branching in both brittle and ductile materials. Peridynamic analysis has been found to be very demanding computationally, particularly for real-world structures (e.g. vehicles, aircrafts, etc.). It also requires a very expensive visualization process. The goal of this paper is to bring awareness to researchers the impact of this cutting-edge simulation tool for a better understanding of the cracked material response. A computer code has been developed to implement the peridynamic theory based modeling tool for two-dimensional analysis. A good agreement between our predictions and previously published results is observed. Some interesting new results that have not been reported earlier by others are also obtained and presented in this paper. The final objective of this investigation is to increase the mechanics knowledge of self-similar and self-affine cracks.

Master of Science / Department of Electrical and Computer Engineering / Balasubramaniam Natarajan / This thesis proposes an automated crack detection and classification algorithm to detect durability cracking (“D”-cracking) in pavement by using image processing and pattern recognition techniques. For the Departments of Transportation across the country, efficient and effective crack detection is vital to maintaining quality roadways. Manual inspection of roadways is tedious and cumbersome. Previous research has focus on distinct transverse and longitudinal cracks. However, “D”-cracking presents a unique challenge since the cracks are fine and have a distinctive shape surrounding the intersection of the transverse and longitudinal joints. This thesis presents an automated crack detection and classification system using several known image processing techniques. The algorithm consists of four sections: 1) lighting correction, 2) subimage processing, 3) postprocessing and 4) classification. Some images contain uneven lighting, which are corrected based on a model of the lighting system. The region of interest is identified by locating the lateral joints. These regions are then divided into overlapping subimages, which are then divided into cracked and noncracked pixels using thresholds on the residual error. Postprocessing includes a row/column sum filter and morphological open operation to reduce noise. Finally, metrics are calculated from the final crack map to classify each section as cracked or noncracked using the Mahalanobis distance from the noncracked distribution.

The mechanical engineering department at the University of Idaho is conducting a project with the purpose of developing a complete system for investigating creep-, creep-fatigue- and fatigue properties of metallic materials at elevated temperatures up to 650 ˚C with Compact Tension (CT) specimens. Considerable efforts have been made to study and understand these phenomena, although numerous problems still exist. It is important to explore more extensively the complicated phenomena of creep, fatigue and of creep-fatigue interactions. The Direct Current Potential Drop (DCPD) method is a common method used to investigate, for example, the initiation of cracks, crack growth rates and to monitor crack growth. The technique utilizes the fact that the electrical resistance of a CT specimen changes with crack growth. By applying a constant current over the specimen and measuring the resulting voltage over the crack, the crack length can be related to the voltage, and the difference in crack length with difference in voltage. Standards from the American Society for Testing of Materials (ASTM) were used as guidance when designing the DCPD system and CT specimen. The development and implementation processes were divided into an analytical and an experimental stage. The final product consisted of a high temperature extensometer, to measure crack mouth opening displacement (CMOD), and a DCPD system, to measure crack growth, controlled by separate control units. The DCPD system consisted of a DC supply and a nano voltmeter along with Constantan wire and NiCr60 wire respectively, that were mechanically fastened. The DCPD system delivered overall satisfying results and was able to generate sufficient data to produce a crack growth curve, da/dN vs. ΔK. Although, by taking advantage of resistance welding equipment to attach the DCPD wires, along with implementing one shared control unit for the DCPD system and the extensometer, more accurate and accessible measurements and correlations could be extracted. / Mechanical engineering avdelningen på University of Idaho genomför just nu ett utvecklingsprojekt med syftet att utveckla ett komplett system för undersökning av krypnings, krypnings-utmattnings- samt utmattnings- egenskaper av metalliska material vid höga temperaturer upp till 650 ˚C med hjälp av kompakta spänningsprovstavar (CT specimens). Betydande ansträngningar har gjorts för att undersöka och förstå dessa fenomen, men flera problem kvarstår. Det är viktigt att djupare undersöka kopplingen mellan krypnings- och utmattningsegenskaper. Direct Current Potential Drop (DCPD) metoden är en vanlig metod vilken används för att undersöka, exempelvis, sprickinitiering, spricktillväxthastigheter och spricktillväxt. Tekniken utnyttjar faktumet att den elektriska resistansen i en provstav ändras med spricktillväxt. Genom att föra en konstant ström genom provstaven och sedan mäta den resulterande spänningen över sprickan, kan spricklängden relateras till uppmätt spänning. På samma sätt kan spricktillväxt relateras till spänningsförändringar. Standarder från American Society for Testing of Materials (ASTM) användes för att designa ett DCPD system samt en CT provstav. Utvecklings- och implementeringsprocessen var uppdelad i en analytisk och en experimentell del. Den slutgiltiga produkten bestod av en extensometer, för mätning av spricköppning vid höga temperaturer, och ett DCPD system, för mätning av spricktillväxt vid höga temperaturer, vilka kontrollerades av separata kontrollenheter. DCPD systemet bestod av en strömkälla och en nanovoltmeter tillsammans med Constantan kablar respektive NiCr60 kablar, vilka fastsättes mekaniskt. DCPD systemet levererade generellt sett tillfredställande resultat och hade kapacitet att generera tillräckligt precisa data för att producera en spricktillväxtkurva, da/dN vs. ΔK. Däremot, genom att utnyttja en resistanssvets, för att fastsätta DCPD-kablarna, tillsammans med en gemensam kontrollenhet för extensometern och DCPD systemet, kan det tänkas att bättre och mer tillgängliga resultat kunde åstadkommas.