MirMilad Mirsayar

Modified maximum tangential stress criterion for fracture behavior of zirconia/veneer interfaces

The veneering porcelain sintered on zirconia is widely used in dental prostheses, but repeated mechanical loadings may cause a fracture such as edge chipping or delamination. In order to predict the crack initiation angle and fracture toughness of zirconia/veneer bi-layered components subjected to mixed mode loadings, the accuracy of a new and traditional fracture criteria are investigated. A modified maximum tangential stress criterion considering the effect of T-stress and critical distance theory is introduced, and compared to three traditional fracture criteria. Comparisons to the recently published fracture test data show that the traditional fracture criteria are not able to properly predict the fracture initiation conditions in zirconia/veneer bi-material joints. The modified maximum tangential stress criterion provides more accurate predictions of the experimental results than the traditional fracture criteria.

New Approach to Determining Concrete Slab Lift-Off by Use of Interfacial Fracture Mechanics Concepts

Negative temperature gradient and the moisture gradient through the thickness of a concrete slab result in curling and warping of the slab edges to a concave configuration. The tendency of the slab pavement to separate from the subbase layer, called lift-off, is mainly controlled by such environmental effects and the weight of the slab itself. Because of such effects, cracks may propagate at the interface of the concrete slab and the subgrade. The induced stress and displacement fields around the interface crack tip are characterized by the stress intensity factors. The stress intensity factors can then be used in assessment of the cracked bond strength by employing any fracture criteria; therefore, it is necessary that the stress intensity factors be obtained. This paper proposes a new approach for determination of slab lift-off that uses concepts from interfacial fracture mechanics. A two-dimensional finite element analysis was performed to simulate lift-off in concrete slab pavements, and the effect of interface cracking on the mechanism of the lift-off was investigated. The relative stress intensity factors as well as the relative slab lift-off were determined for different crack lengths, loading conditions, and material properties of the slab and the subgrade. The presented model was validated with experiments. This paper discusses the remarkable effects of the material properties and the induced contraction stress on the slab lift-off. The findings presented provide researchers with some insight as to the effect of curing conditions and relative stiffness on slab lift-off and answer some of the primary questions regarding the mechanism of interfacial fracture in concrete slab–subgrade structures caused by the lift-off.

Structural health monitoring for DOT using magnetic shape memory alloy cables in concrete

Embedding shape memory alloy (SMA) wires in concrete components offers the potential to monitor their structural health via external magnetic field sensing. Currently, structural health monitoring (SHM) is dominated by acoustic emission and vibration-based methods. Thus, it is attractive to pursue alternative damage sensing techniques that may lower the cost or increase the accuracy of SHM. In this work, SHM via magnetic field detection applied to embedded magnetic shape memory alloy (MSMA) is demonstrated both experimentally and using computational models. A concrete beam containing iron-based MSMA wire is subjected to a 3-point bend test where structural damage is induced, thereby resulting in a localized phase change of the MSMA wire. Magnetic field lines passing through the embedded MSMA domain are altered by this phase change and can thus be used to detect damage within the structure. A good correlation is observed between the computational and experimental results. Additionally, the implementation of stranded MSMA cables in place of the MSMA wire is assessed through similar computational models. The combination of these computational models and their subsequent experimental validation provide sufficient support for the feasibility of SHM using magnetic field sensing via MSMA embedded components.

Geometry and Determining the Positions of a Plan Transporter Manipulator

The conveyor mechanism (working in a plan) to be presented in this study is a classic case of manipulating conveyor, simply with a single degree of mobility. It is a very common mechanism used in classical mechanics, being encountered at lifting platforms, at handicapped chairs, at cranes, forklifts, automatic machines and machines, or at older steam locomotives where it having the role of reversing the rotation-translation movement. Being a simple, common manipulator, he is also a good teaching example, much used in the student courses of mechanics, mechanisms, robotics-mechatronics. That is why we want to present in this study in a concise way the geometry and the kinematics of this mechanism. There will be a constructive and one kinematic scheme. The mechanism consists of a crank (a motor element 1), an RRR dyad composed of elements 2 and 3 and an RRT dyad formed by kinematic elements 4 and 5. The motor element 1 has a complete rotation (360 degrees) being the single driving feature of the entire mechanism. The element 3 is a bar that links the engine element 1 to the rocker element 2. From the rocker element 2, the movement is forwarded through the rod 4 to the final execution member 5, which is a slider (patina), having the role of oscillating linearly (it can also be a piston in a cylinder). The mechanism can also be used by changing the driving element to the driven one so as to become a motor mechanism with the leading element 5 and when the rotation element 1 to become a final driven element. Thus it can be used as a mechanism for producing the movement and transmitting it with the conversion from the rotation to translation movement. We intend to present this mechanism, in the present paper, when it functions as a manipulator, having the motor element 1 and the final element, the execution element, the patina 5. Special emphasis will be placed on the kinematics of the mechanism, studied on elements, but also on structural groups. Obviously there will be presented and some applications of the mechanism.

Velocities and Accelerations at the 3R Mechatronic Systems

This article presents an original method to determine the speeds and accelerations to structures MP R-3 The structure of the 3R (space) are known (required) rotation speeds of the triggers and must be determined speeds and accelerations of the endeffector M. Starting from the positions of direct kinematic system MP R-3deriving these system of relations in depending on the time, once and then a second time (the second derivation) is first obtains the speeds of the system and for the second time the accelerations endeffector point M. System on which must be resolved has three equations and three independent parameters to determine. Constructive basis is represented by a robot with three degrees of freedom (a robot with three axis of rotation). In the case where a study (analysis) a robot anthropomorphic with three axis of rotation (which represents the main movements, it is absolutely necessary), already has a system of the basis on which it can add other movements (secondary,). All calculations have been arranged and in the form of the array.