Lower Torsional Strength Research Articles

Effect of functionalized graphene addition on mechanical and thermal properties of high density polyethylene

Abstract High density polyethylene (HDPE)/graphene nanocomposites were successfully synthesized by compounding of HDPE, as polymer matrix, with hexamethylenediamine functionalized graphene. The resulting nanocomposite was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and thermal gravimetric analysis (TGA) techniques. SEM characterization confirmed the good dispersion (homogeneous and uniform) of graphene in the polyethylene matrix. The TGA technique revealed a slight improvement in thermal resistance. Functionalized graphene improved a better thermal stability of HDPE (up to 6 °C) than non-functionalized graphene (up to 2 °C). Mechanical tensile and torsion tests showed that HDPE/functionalized graphene nanocomposites exhibit high tensile strength and low torsional strength compared to HDPE/non-functionalized graphene nanocomposites. Compared to pure HDPE, the Young’s modulus increased by 80% and 30%, whereas, the torsion modulus increased by about 34% and 44% for the HDPE/functionalized and HDPE/non-functionalized graphene, respectively. Regardless of this increase, it can be seen that the torsion modulus of HDPE/non-functionalized graphene is much higher than that of HDPE/functionalized graphene.

Cyclic fatigue and torsional strength of three different thermally treated reciprocating nickel-titanium instruments.

The aim of this study was to evaluate the cyclic and torsional fatigue resistance of the reciprocating single-file systems Reciproc Blue 25.08 (VDW GmbH, Munich, Germany), Prodesign R 25.06 (Easy Dental Equipment, Belo Horizonte, Brazil), and WaveOne Gold 25.07 (Dentsply/Tulsa Dental Specialties, Tulsa, OK, USA). Sixty reciprocating instruments of the systems Reciproc Blue R25 (RB #25 .08 taper), Prodesign R (PDR #25 .06 taper), and WaveOne Gold (WOG #25 .07 taper) (n = 20) were used. Cyclic fatigue resistance testing was performed by measuring the time to failure in an artificial stainless steel canal with a 60° angle of curvature and a 5-mm radius located 5mm from the tip (n = 10). The torsional test (ISO 3630-1) evaluated the torque and angle of rotation at failure of new instruments (n = 10) in the portion 3mm from the tip. The fractured surface of each fragment was also observed using scanning electron microscopy (SEM). In addition, a supplementary examination was performed to measure the cross-sectional area of each instrument 3 and 5mm from the tip. The data were analyzed using one-way ANOVA and Tukey's test, and the level of significance was set at 5%. The cyclic fatigue resistance values of PDR 25.06 were significantly higher (P < 0.05). RB 25.08 showed higher fatigue resistance than WOG 25.07 (P < 0.05). The torsional test showed that PDR 25.06 had lower torsional strength (P < 0.05). No differences were observed between RB 25.08 and WOG 25.07 (P > 0.05). PDR 25.06 showed higher angular rotation values than RB 25.08 and WOG 25.07 (P < 0.05). RB 25.08 presented higher angular rotation than WOG 25.07 (P < 0.05). The cross-sectional area analysis showed that PDR 25.06 presented the smallest cross-sectional areas at 3 and 5mm from the tip (P < 0.05). PDR 25.06 presented the highest cyclic fatigue resistance and angular rotation until fracture compared to RB 25.08 and WOG 25.07. In addition, RB 25.08 and WOG 25.07 had higher torsional strength than PDR 25.06. In endodontic practice, thermally treated reciprocating instruments have been used for the root canal preparation of curved and constricted canals; therefore, these instruments should present high flexibility and suitable torsional strength to minimize the risk of instrument fracture.

Behaviour of Partially Closed Stiffened Cold-Formed Steel Compression Member

Usually, thin-walled open column sections have an intrinsic weakness in their low torsional strength, which is unpleasant for resistance of an open section. The distortion behaviour of cold-formed steel open section has a significant role in structural steel design. Hence, initiativeness is made for converting partially closed section by adding simple spacer plates connected with self-tapping screws. The intend of this work is tested to estimate the competence of this solution by comparing the strength and performance of partially closed and open stiffened complex channel section under axial compression. The buckling characteristics of the section are computed using the linear elastic buckling analysis program CUFSM. The resistance and behaviour of the intermediate columns are examined in detail using finite element analysis software ANSYS. A good conformity between finite element analysis and experiments is found. The nominal design capacities are evaluated using the necessities of the direct strength method, North American iron and steel specification and Indian standard and are compared with those from test and finite element analysis. After this verification of the numerical model, a crucial parametric study is carried out to inspect the effect of vitiations on thickness, depth, spacing and slenderness of spacer plates. The particulars of this study and results are offered in this research article.

Algorithm for the analysis of deformations and stresses due to torsion in a metal beam from LIDAR data

An interesting field for application of LIDAR technology is structural health monitoring, especially in the study of deformation and stress in the beams. In the beams, it is not only the deformation due to bending that is an issue of control but it is also important to check the deformation due to torsion, particularly in open cross sections such as I, U, L, which have a very low torsional strength. This paper presents a new algorithm for obtaining, automatically and separately, the deformations in a beam subjected to torsional and bending loading, respectively, from LIDAR data. With the values of the deformation found by the new developed algorithm, the shear stresses are obtained. The methodology presented in this paper has been tested with a real beam in a laboratory under different load situations. The results obtained from the algorithm were compared not only with measurements by direct methods but also with results obtained by FEM simulation of the 3D model of the beam. The results found by the new algorithm compare with the other methods; therefore, this verifies the validity of the method for applications of structural health monitoring of metal structures. Copyright © 2015 John Wiley & Sons, Ltd.

Vibration test and assessment for an ocean drilling rig derrick: Taking the ZJ50/3150DB drilling rig as an example

Abstract The rig derrick of a ZJ50/3150DB drilling rig in an offshore jacket platform located in the Bohai bay vibrates obviously when drilling. In order to assess the safety of the derrick when drilling, vibration test for the derrick was carried out and a finite element model of the derrick was built to analyze the impact of vibration on the derrick's structure safety, in combination of the field test data with the calculation results got using the model. Natural frequency, amplitude-frequency response when drilling, vibration amplitude and vibration acceleration of the derrick were tested. Based on the derrick drawing and field situation, the finite element model of the derrick structure was built using ANSYS software. The first-order natural frequency of the derrick calculated using the model was 0.555 8 Hz, which coincided with the filed test data and proved the validity of the model. The analysis of the field test data and the calculation results, show, the derrick is resonance-prone when the rotation speed of the top drive is 36 r/min, the derrick C-style opening has low torsional strength, the two front brace rods of the derrick substructure are crucial components that concern the derrick safety, and derrick vibrations under different working conditions and shock vibration happening when the top drive passing by the monkey board meet safety requirements.

Are Inflatable Nails an Alternative to Interlocked Nails in Tibial Fractures?

Recently developed inflatable nails avoid reaming and interlocking screws in tibial fractures and reflect a new principle for stabilization of long bone fractures. We asked if the bending stiffness, rotational rigidity, or play (looseness of rotation) differed between an inflatable versus large-diameter reamed interlocked nails, and whether the maximal torque to failure of the two bone-implant constructs differed. In a cadaveric model, we compared the biomechanical properties with those of an interlocked nail in eight pairs of fractured tibial bones. Bending stiffness, rotational rigidity, play (looseness in rotation), and torsional strength within 20 degrees rotation were investigated using a biaxial servohydraulic testing system. For all biomechanical variables, we found a large interindividual variance between the pairs attributable to bone quality (osteoporosis) for both fixation methods. The inflatable nail had a higher bending stiffness, with a mean difference of 58 N/mm, and a lower torsional strength, with a mean difference of 13.5 Nm, compared with the locked nail. During torsional testing we noted slippage between the inflatable nail and bone. We observed no differences in play or rotational rigidity. Given the lower torsional strength we recommend caution with weightbearing until there are signs of fracture consolidation.

Seismic Behavior and Retrofit of Outrigger Knee Joints

Experimental tests were conducted on six 1/3-scale specimens to define the vulnerabilities of existing outrigger bents under in-plane and out-of-plane seismic loading and to develop retrofit measures that address the identified vulnerabilities. The specimens represented knee joints in the SR 99 Spokane Street overcrossing in western Washington State but included deficiencies present in a number of older bridges. The as-built specimens failed at low ductility levels due to shear distress, low torsional strength of the outrigger beam, and reinforcement bond failures within the joint. Threshold principal tension stress values describing the expected condition of the joints were established and compared to values obtained by other researchers. Circular steel jackets were used to retrofit the as-built specimens. The retrofitted specimens developed plastic hinging in the column, with enhanced strength, energy, and ductility capacities. Design and detailing guidelines for retrofitting outrigger bents were proposed.

Appropriate osteotomy site and number in limb lengthening.

The effects of the placement of osteotomy site on osteogenesis during monofocal and bifocal lengthening were investigated in 47 immature rabbits allocated to 4 groups according to osteotomy site: (1) monofocal in the proximal diaphysis; (2) monofocal in the distal diaphysis; (3) bifocal in the proximal and distal diaphysis; and (4) bifocal in the proximal diaphysis. The right tibia was distracted at an overall rate of 1.0 mm per day for 15 days. These groups were compared by assessment of soft radiograph findings and torsional strength 2 and 6 weeks after the end of distraction. Microangiography was done in 5 rabbits in the bifocal proximal and distal group. The proximal distracted site showed favorable bone regeneration compared with the distal site, and torsional strength was significantly greater in the proximal than in the distal osteotomy group. Less bone formation and lower torsional strength were observed in the bifocal proximal diaphysis group, with short intermediate segment, than that in the other bifocal group, with long intermediate segment. The nutrient artery in the latter group was preserved in the intermediate segment and reanastomosed to the metaphyseal arteries. These results suggest that the proximal diaphysis is more suitable for the osteotomy site than is the distal diaphysis. In a 2-level osteotomy, the inflow site of the nutrient artery should be included within the intermediate segment.

Curved Beams

A type of structure for which no general method of analysis appears to be available is that of a curved beam of low torsional strength and stiffness supported by a torque box. This note outlines ways of analysing two simple cases.