In aeronautical and automotive industries the use of RIVETs for applications requiring several joining points is now very common. In spite of a very simple shape, a RIVETed junction has many contact surfaces and stress concentrations that make the local stiffness very difficult to be calculated. To overcome this difficulty, commonly finite ELEMENT models with very dense meshes are performed for single joint analysis because the accuracy is crucial for a correct structural analysis. Anyhow, when several RIVETed joints are present, the simulation becomes computationally too heavy and usually significant restrictions to joint modelling are introduced, sacrificing the accuracy of local stiffness evaluation. In this paper, we tested the accuracy of a RIVET finite ELEMENT presented in previous works by the authors. The structural behaviour of a lap joint specimen with a RIVET joining is simulated numerically and compared to experimental measurements. The RIVET ELEMENT, based on a closed-form solution of a reference theoretical model of the RIVET joint, simulates local and overall stiffness of the junction combining high accuracy with low degrees of freedom contribution. In this paper the RIVET ELEMENT performances are compared to that of a FE non-linear model of the RIVET, built with solid ELEMENTs and dense mesh, and to experimental data. The promising results reported allow to consider the RIVET ELEMENT able to simulate, with a great accuracy, actual structures with several RIVET connections.

Strength reduction in structures like an aircraft could be resulted as cyclic loads over a period of time and is an important factor for structural life prediction. Service loads are emphasized at the regions of stress concentration, mostly at the connection of components. The initial flaw prompting the service life was expected by using the Equivalent Initial Flaw Size (EIFS), which has been recognized as a powerful design tool for life prediction of engineering structures. This method was introduced 30 years ago in an attempt to study the initial quality of structural details. In this paper, the prediction of life based on failure mechanics in a RIVETed joint has been addressed through the concept of EIFS. For estimation of initial crack length by EIFS, extrapolation method has been used. The EIFS value is estimated using the coefficient of cyclic intensity (Δ K) and using the cyclic integral (Δ J), and the results are compared with each other. The simulation results show that the if the coefficient of tension been used in EIFS estimation, which based on the Paris law, the EIFS value will be dependent on the loading domain, while the use of the J-Cyclic integral in the EIFS decrease its dependence on the load domain dramatically.

Till now, various models have been proposed in literature to simulate the behavior of RIVETed structures. In order to find the most accurate analytical method in modeling the dynamic behavior of RIVETed structures, a comparison study is performed on several of these models, in this research. For this purpose, experimental modal analysis tests are conducted on a RIVETed plate to verify the efficacy of the analytical models. Moreover, finite ELEMENT model updating is used to reduce the difference between analytical and experimental results. First, the material properties of plates are optimized using the experimental results obtained from modal tests of a simple plate. Next, the optimization is performed for the physical properties of RIVET. At the end, it is concluded that the fastener model proposed by Rutman can bring about the most accurate results when it is used in combination with solid plates and gap ELEMENTs in the contact region.

Objective: CREB1 is an important downstream protein for many signaling pathways. By designing efficient siRNAs against CREB1, it may be possible to assess the role of molecules involved in signaling pathways in different cell types. In this research the efficiency of CREB1 knockdown by two different siRNAs in K562 cells has been studied. Materials and Methods: siRNAs have been designed according to the criteria suggested by Reynolds et al. K562 cells were transfected by siRNA using Lipofectamine 2000. The efficiency of CREB knockdown has been assessed by quantitative relative Real-time PCR. Results: Our results have shown that only one of the siRNAs has a high level of inhibitory effect on CREB1 gene expression. The expression of CREB1 by this siRNA was knocked-down by 87% in K562 cells. Conclusion: In this research, although two siRNAs were designed according to the Reynolds et al. criteria, only one showed an inhibitory effect. Reasons other than the aforementioned criteria may be involved in effectiveness of siRNAs.

Changes of up to 80°C has been reported for oral cavity temperature. This could well effecti on the nature of restorations for example failure of bonding of adhesive restorations. It is advocated that using opaque layer in porcelane to restorations could reduce this problem. This experimental study was designed to evaluate the effect mentioned using finitELEMENT analysis method.Results showed that cooling has a more destructive effect than warming process restorations with the presence of opaque having a finitELEMENT analysis effect on restorations.

Metal sheets play an important role in the mechanical design, particularly in the aerospace structures. Various parameters affect the quality of this operation. In this paper, optimization of the parameters contributing to the RIVETing quality in order to minimize the value of the maximum tangential stress in metal sheets is addressed. hence, the tolerance of the hole diameter in top and bottom sheets, the friction coefficient, and the tolerance of the RIVET diameter and the RIVET length were considered as the parameters influencing the RIVETing quality. A total of 64 models were obtained by permutations of the parameters, two at a time. The outputs were determined using finite ELEMENT method. The objective function for optimization is the maximum tangential stress for which there is no analytical relation. Thus, three methods including the multivariable linear regression (MLR), the artificial neural network model of the radial basis function (RBF) type, and the hybrid model of the artificial neural network and the genetic algorithm (ANN-GA) were employed to model this function. Further, the performance of the three models was compared and the most suitable one was selected to model the objective function. The regression model was used to model the values of the height and the diameter after RIVETing. The imperialist competitive algorithm is utilized to solve this optimization problem. The obtained value for the maximum tangential stress using the imperialist competitive algorithm is 16368 pounds per square inches. After modification, this value increased to 23440 pounds per square inches using the finite ELEMENT method. After RIVETing, the height and diameter of the RIVET were respectively measured to be 0.07689 inches and 0.18524 inches.

In this paper, experimental investigation was performed to estimate fatigue life of single and double RIVETed coach peel joints of 2024 aluminum alloy. Load controlled fatigue tests were conducted with load ratio and frequency of 0. 1 and 10 Hz, respectively. Failure of the specimens revealed three major modes of folded region fracture (A-type), fracture from edge of the RIVET hole (B-type) and mixed mode fracture (A & B). Although all failure modes contributes equally in single RIVETed joint, mixed mode fracture was observed as dominant mode in two RIVETed ones. A numerical approach is applied to estimate fatigue life of RIVETed coach peel joints. Finite ELEMENT analysis was implemented by ABAQUS as the first step of this approach to estimate stress distribution, stress concentration factor, stress and strain amplitude. Fatigue lives were then calculated using three fatigue life theories of Monson-Hirschberg, Smith-Watson-Topper and Morrow. Finally, good accordance between numerical and experimental results revealed that the finite ELEMENT approach combined with fatigue life theories is capable for fatigue life prediction. It is concluded that adding a RIVET in longitudinal direction to the single RIVETed coach peel joint decreases the life cycles by increasing the stress concentration factor. Moreover, results of finite ELEMENT approach showed that Monson-Hirschberg and experimental data has the best agreement in compare with SWT and Morrow.

Background and Aim: The movement of molars has been evaluated in many studies to correct Cl II malocclusion by non-compliance appliances but the results are controversial. The aim of this study was to compare the upper first and second molars' movement in cervical headgear (HG) and pendulum appliance (PEND) by finite ELEMENT method.Materials & Methods: For modeling process, one of the best dry skulls was CT scanned (l mm slices). Modeling was done according to the mechanical properties of cortical and trabecular bone of maxilla and PDM and teeth and transferred to computer by scanner. ELEMENTing, meshing and loading was done. The magnitude of force for both appliances was 250 gr and line of force for HG was 20 degree above the occlusal plane action and for PEND was along the midlingual surface of upper first molar crown. Tooth movement analysis was performed by the software named Ansys 5.71.Results: The amount of dislocation of the 1st molar cusps tip (mesiobuccal, mesiopalatal, distobuccal, distopalatal) at presence of second molar in bucco-lingual dimension showed distal-in rotation in HG and mesial-in rotation for pendulum. In mesio-distal dimension, the four cusps of 1st molar moved distally in HG and palatal cusps moved more in PEND. In vertical dimension, 1st molar showed extrusion in HG and intrusion in PEND for distal cusps.Conclusion: The presence of second molar had impact on the quality of upper first molar in both appliances and it moved in a distal direction, extruded and buccal drifted in both of them. Therefore, with regard to the cooperation of the patients, pendulum appliance is recommended to correct Cl II malocclusion instead of cervical headgear.