Crashworthiness Analysis of Octagonal-Inner Double Tube with different thickness under Off-Axis Oblique Load

The crash tube is one of the important parts to reduce the effects of accidents. The design of crash tube only watches the frontal crash, but oblique crash might affect the passengers. Besides, Lack of oblique-loading researches in crashworthiness becomes causes to analyze crash tubes more. This paper aims to study crashworthiness performance of octagonal-inner double tubes under off-axis oblique impact load (0°, 10°, 20°, and 30°). The tubes have been connected with two walls, top wall as moving wall and a bottom wall as rigid wall underl different load angles. The tubes were made from Aluminum Alloy and consisted of a circular-outer tube and an octagonal-inner tube. The crashworthiness parameters of absorption of specific energy (SEA), maximum collapse force (Fmax) and efficiency of crush force (CFE) were obtained for all the structures. In order to get the value of parameters, the method of finite element analysis was used. The effects of different thickness of 1 mm, 2 mm, 3 mm and 4 mm and various oblique were studied. Based on numerical results, structures of 4 mm thickness were the greatest SEA of 26.39 kJ/kg among other thickness of structures. In addition, the value of energy absorption for tubes obliquely loaded decreased for all the size of thickness structures. Finally, this structure can be considered as crash box of vehicle in future

Comparison of Three Types of Stud Attachments on Retention and Strain Energy in the Mandibular Implant-Supported Overdentures

Background: The present in vitro study assessed he effects of three different Stud attachments on the retention and strain energy in the mandibular implant-supported overdentures. Methods: Two parallel implants (Implantium System) were placed on the mandibular canines’ regions and a chrome-cobalt casting framework was prepared as the denture base. The implant fixtures were installed on the canine location and the pulling was performed by three orthodontic wires in the Instron machine with a speed of 0.5 min/mm. Dislodging forces were applied to the housings in two vertical and oblique directions on three different Stud attachments (Ball, Kerator, Positioner). All three wires were connected to the device in the vertical position while one wire was separated from the molar’s region in the oblique loadings. The retention of these three attachments was statistically analyzed by means of one-way analysis of variance. Results: Significant differences were found between the attachments (F (2, 15) =33.01, p<0.0001). Furthermore, Retention forces in the oblique loadings were significant differences between the attachments (F(2,15)=175.10, p<0.0001). The effect size, calculated using eta squared, was 0.95, which is considered large. The strain energy was 4.08, 3.05 and 1.04 J for the Ball, Positioner and Kerator attachments in the vertical loadings and 4.05, 1.44 and 3.07 J in the oblique loading respectively. Conclusion: The retentive forces and strain energy of ball attachments were greatest than other studied attachments in the vertical and oblique loadings.

Energy absorption of thin-walled circular tubes with gradient thickness under oblique loads

Introducing nonuniform thickness has shown promising potential in enhancing the energy absorption of thin-walled tubes. However, existing studies were focused on the axial loading, with little attention being paid to the oblique loading condition. In this paper, the energy absorption performance and the deformation modes of the circular tubes with gradient thicknesses under oblique loads are investigated. Finite element simulations and experiments were carried out for both uniform-thick and gradient-thick tubes under the axial and oblique loads, and satisfactory agreement was achieved betweent the numerical and the experimental results. The validated finite element models were used to investigate the effects of the thickness gradient and loading angle on the deforamtion modes and the energy absorption. The results highlight the advantages of the gradient-thickness tubes in improving the energy absorption performance under the oblique loading condition, especially at a larger loading angle. A novel progressive bending deformation mode was observed for the tube with large thickness gradient at a loading angle larger than 15°, which is beneficial for the energy absorption performance.

Experimental and numerical assessment of oblique loading quasi-static testing of railway anticlimbers

An oblique loading angle test was devised in order to subject the anticlimbers of railway vehicles to a predetermined perpendicular load as well as a predetermined bending moment. The motivation for this type of test was the Standard and industry requirements for anticlimbing devices to prevent overriding and resist a determined perpendicular force while dissipating energy. Anticlimbing units, based on shrinking circular deformation tubes, were subjected to compression tests. The oblique loading was applied by placing the anticlimbing unit on a plate at an angle to the centreline of the unit. A numerical model was validated against the test results, in order to infer the bending moment subjected to the anticlimber unit. The bending moment on the anticlimbers was expected to be fully determined by the perpendicular force and the length of the tube. The predicted bending moment measured by the validated numerical model was smaller than anticipated and was potentially unpredictable. The discrepancy was caused by the irregular distribution of the normal force at the interface of the test machine and the anticlimber head. As a result, the devised angle test was proved unsuitable to induce a consistent and predictable bending moment on the anticlimber units of railway vehicles.

Comparison of stress distribution in a three unit cement retained implant supported prosthesis with different implant abutment connections: A photoelastic analysis

Aim: With the emphasis on success of implant supported prosthesis, and health of the surrounding tissues that are related to accuracy, and fit between the implant components, stability at implant abutment interface is of prime importance. The aim of this study is to evaluate and compare the stress distribution in three unit cement retained implant supported fixed partial denture with different implant abutment connections through photo elasticity. Materials and methods: Two photo elastic resin models were fabricated of standard dimensions (44mmx22mmx10mm). Group I sample: Three unit cement retained implant supported fixed partial denture with Internal implant abutment connection (Internal hexagonal connection) (Paltop Advanced, Keystone Dental Company, US)Group II sample: Three unit cement retained implant supported fixed partial denture with conical Morse taper connection (1.5 degree Morse taper) (Paltop Conical Active, Keystone Dental Company, US). Three unit cement retained implant supported fixed partial denture simulated missing mandibular first molar. Axial and oblique loads of 100N were placed on each implant and pontic area for 10 sec. Ten tests were done for each group. The stress values around the implants were derived from the colored fringe patterns obtained through polariscope, which were photographed after load applications from which values were derived. Results: Under axial loading, there was statistically significant difference between internal hexagonal connection and Morse taper connection in three unit implant supported prosthesis. Stresses were more in Group II sample with Morse taper connection. Under oblique loading, there was no statistically significant difference between Group I and Group II samples. Conclusion: Within the limitations of this in vitro study, it can be concluded that Internal hexagonal connection showed less stresses as compared to Morse taper connection in a three unit cement retained implant supported prosthesis. Stresses were concentrated more in apical area under axial loading; while under oblique loading stresses were seen on the side of application of force on the body of the implant and on the apical region. However, stresses were uniformly distributed in both groups I and group II samples. In both groups stresses under oblique loading were more than axial loading, but that was not statistically significant.