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Friction Stir Welding Process
Published in Noor Zaman Khan, Arshad Noor Siddiquee, Zahid A. Khan, Friction Stir Welding, 2017
Noor Zaman Khan, Arshad Noor Siddiquee, Zahid A. Khan
Yield strength is the stress that corresponds to the yielding of the material. Tensile test can determine UTS, yield strength, and measures of ductility such as percent elongation and reduction in area. Typical stress–strain curve for aluminum 5754 is shown in Figure 2.25. It is an important test for measuring quality of welded joint. Fracture location of the tensile test sample clarifies the cause of failure that can be confirmed through microstructural examination. Tensile test requires standard designed specimen as per ASTM standard. Generally, ASTM E8M is used for testing metallic samples. Tensile samples are usually prepared using wire electrical discharge machining due to its good accuracy and ability to machine any metallic material. Welded samples are tested on tensile testing machine (e.g., a tensometer). Tensometer is a device used to evaluate tensile properties (strengths and ductility) of materials. In FSW, tensile strength of joint is measured and compared with that of BM to determine the efficiency of the joint. Typical tensile specimen for metal is shown in Figure 2.26.
Strain and Stress in One Dimension
Published in Jenn Stroud Rossmann, Clive L. Dym, Lori Bassman, Introduction to Engineering Mechanics, 2015
Jenn Stroud Rossmann, Clive L. Dym, Lori Bassman
Engineers include safety factors in designs. A safety factor is a margin of insurance against unforeseen conditions, material imperfections, fabrication errors, and other uncertainties. The allowable (actually induced) stress in a design must be less than the failure strength or (more conservatively) the yield strength. The safety factor is simply the ratio of failure (or yield) strength to the allowable stress in the current loading conditions (a limit determined from several factors, including material properties, confidence in load prediction, type of loading, possible deterioration, and design life of the structure). Although different applications have different established values, safety factors should have values over 2.0 in robust designs. That is, our analysis should assure us that the allowed stress will never exceed half of the reference (failure or yield) value. For higher-risk applications, we may prefer to use higher safety factors, which can reduce the risk but also increase costs, requiring engineers to use their judgment to make ethical and judicious tradeoffs.
Semi-Submersibles under Impact Loads
Published in Srinivasan Chandrasekaran, Offshore Semi-Submersible Platform Engineering, 2020
Column members of the semi-submersible are modeled as a stiffened, cylindrical shell, and the analysis is carried out under lateral impact forces in the Arctic region. The cylindrical shell is modeled using polar class, high-tensile steel of grade DH36, based on the material properties available in the literature. The mechanical properties of DH36 steel at RT and –60°C at 0.001/s strain rate are listed in Table 4.9 (Kim et al., 2016). It is evident that the yield strength increases with the decrease in temperature. True stress-strain curves, representing the basic plastic flow characteristics of the material at room temperature and the Arctic temperature, are shown in Figure 4.38. They are used to define the material properties to predict the deformation characteristics.
Finite element analysis and nanomechanical properties of composite and ceramic dental onlays
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Cem Peskersoy, Heval Makbule Sahan
The yield strength corresponds to the point at which the material deforms only elastically under applied stress. Once this point is passed, nonreversible deformation occurs until the fracture point (toughness). In the present study, both the yield strength and fracture toughness of ZRC were the highest among the groups. Although PIC and RNC exhibited similar fracture toughness, IRC exhibited statistically significant differences from the rest of the study groups. Sonmez et al. (2018) indicated that ceramic-resin composite materials have lower hardness and fracture toughness than glass-matrix ceramics. Due to the unequal distribution of fillers in the body of the surface of the composites, weak spots and RCMs become vulnerable to fracture. RCMs and hybrid-resin composites have lower surface hardness and fracture toughness than ceramic materials, which would be one of the main consequences of the nonhomogeneous distribution of the fillers (Al-Harbi et al. 2017).
A parametric study on the dynamic ultimate strength of a stiffened panel subjected to wave- and whipping-induced stresses
Published in Ships and Offshore Structures, 2021
George Jagite, Fabien Bigot, Quentin Derbanne, Šime Malenica, Hervé Le Sourne, Patrice Cartraud
The main objective of this paper is to analyse the dynamic ultimate strength of a stiffened panel subjected to wave- and whipping-induced stresses. Hence, it is essential to differentiate the two main dynamic effects: inertia and strain rate. First, the inertia of the structure affects the structural response, and mainly the amplitude of the internal load, which can be higher or lower than the applied external load. Second, the strain rate effect represents the dynamic enhancement of the yield strength and increases when the loading speed increases. It was proven in Jagite et al. (2019a) that the inertia effect over the ultimate strength of a stiffened panel is negligible for a load period varying from 1 to 16 s. Thus it can be said that the dynamic capacity increase is due to the strain rate effect.
Biomechanical assessment of screw safety between far cortical locking and locked plating constructs
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Yuping Deng, Hanbin Ouyang, Pusheng Xie, Yanfang Wang, Yang Yang, Wenchang Tan, Dongliang Zhao, Shizhen Zhong, Wenhua Huang
The safety factor is a ratio of yield strength to intended load for the actual item that was designed (Macciotta 2018). The allowable strength design method and probability ultimate-state design method have been used in mechanical engineering and civil engineering (Committee 1988), and these methods should be used for assessing and designing medical instruments as well. In our results, the stress of the FCL constructs was significantly higher than that of the LP constructs at all locations, and the von Mises stress of the FCL screw exceeded the allowable stress of the material. However, the critical threshold stress causing bone resorption remained unclear and human bones will grow and heal by themselves, fracture healing models at bone-screw interface are always irreproducible in the laboratory and almost impossible to perfectly validate. There is currently no definitive mathematical or mechanical model of fracture healing for computational simulation as the fracture healing models at bone-screw interface. Fracture fixation is a tradeoff between fracture healing and constructs failure. And considering models under high cycle fatigue loading conditions would make the true failure mechanism more complex and unpredictable. Thus, we focused on assessment of the screws and metal implant safety issues only. Further investigation should pay more attention to the bone-screw interface stress issues for the far cortical constructs