Pure Torsion Research Articles

A novel semi-analytical method for notch stress and fatigue strength analysis of tube-flange welded joints

This paper presents a semi-analytic method to rapidly estimate the notch stress and fatigue strength for tube-flange welded joints. Considering the stress singularity effect at the weld toe, the parameters related to geometry and opening angle are simplified as singular intensity factors. The equivalent singular intensity factors can be fitted by the stress distribution rather than the peak stress at the corner. On this basis, the modified notch stress formulas for tube-flange welded joint (TFWJ) under pure bending or torsion load were fitted and verified. Meanwhile, the simple relationships between singular intensity factor, notch stress intensity factor, strain energy density and peak stress were further deduced, separately. The comparison results show that the fatigue assessment parameters calculated by the traditional approaches and the proposed method are in good agreement. Finally, four groups of fatigue data of TFWJs were summarized to verify the simplified assessment formulas.

Ultimate strength envelope of a 10,000TEU large container ship subjected to combined loads: From compartment model to global hull girder

The main objective of this research is to figure out the relationship of the ultimate strength characteristics between the compartment hull girder and the global hull girder, especially focusing on the ultimate strength envelope of the global hull girder of a 10,000TEU ultra large container ship subjected to combined loads, which is one of the most important indexes to quantify the safety margin of the container ship. To achieve these aims, both the compartment hull girder and the global hull girder are modeled based on true ship hull girder's configurations. A series of full-scale nonlinear finite element analyses are performed. In addition, to examine the reliability of the elastic-perfectly plastic material models employed in FEA, similar scale model collapse experiments of a compartment hull girder subjected to pure hogging and pure torsion are also presented. Finally, the ultimate strength envelope of the global hull girder of the 10,000TEU ultra large container ship subjected to combined vertical bending and torsion is quantitatively obtained, which can characterize the container ship hull girder's ultimate strength interactions between vertical bending and torsion and quantify the safety margin of the global hull girder of the container ship subjected to combined vertical bending and torsion.

J-integral measured from experimental torque load versus torque-ends rotation angle obtained from a spiral notch torsion test

Spiral Notch Torsion Test (SNTT) was developed to measure the intrinsic fracture toughness of structural materials using small specimens. The SNTT system operates by applying pure torsion to cylindrical specimens with a notch line that spirals around the specimen at a 45° pitch. 3-D finite-element analysis has been used to estimate the fracture toughness obtained from SNTT test specimen with 3-D non-coplanar crack front. Here a newly developed SNTT protocol to estimate J-integral directly from the experimental torque load versus torque-ends rotation angle trend curve without the aid of 3-D finite element analyses is presented and its applicability is illustrated by applying it for the evaluation of fracture toughness of SS304/308 weldment. The estimated JQ’ for the SS304/308 weld is 144.2 kJ/m2, which is consistent with that obtained from CT specimen.

TORSION ENHANCEMENT OF REINFORCED SELF-COMPACTING CONCRETE BOX BEAMS USING INTERNAL FRAMED STEEL STIFFENING RIBS

Researches concerning internal torsional strengthening of box beams are very little, since few researchers may study such method of strengthening. This research adopts employing of internal Framed Steel Stiffening Ribs (FSSRs) to strengthen reinforced Self-Compacting Concrete (SCC) box beams subjected to pure torsion. These FSSRs were fabricated to be fully bonded with SCC through using of bolts as shear connectors. Four specimens (the first was a reference one with no strengthening and the other three were strengthened with one, three and five FSSRs, respectively) of reinforced SCC were tested under effect of pure torsion up to failure. All specimens have the same dimensions and reinforcement. The effect of FSSRs presence and their number on torsional capacity was studied. Also, applied torque-angle of twist relation at end, quarter and mid span were studied. Test results show that the ultimate torsional capacity is increased by 45.7 %, 75.5 %, and 122.4 % for specimens strengthened with one, three and five FSSRs, respectively, as compared with reference specimen. Presence of FSSRs tends to reduce deformations where deformations decrease with increasing of FSSRs number. It is concluded that the torsional capacity of a reinforced SCC box beams can be enhanced using internal Transverse FSSRs. The number of used internal FSSRs have main effect on the amount of enhancement.

Investigation of Torsion behavior of high strength short fiber reinforced concrete deep beams with openings

This study aims is to investigating the structural capacity of fibbers reinforced deep beams with opening under pure torsion. The deep beams were made of high strength concrete. The openings were made in the web with different shapes (circular and square), sizes and located at the mid span. Seventeen deep beam specimens were casted and they experimentally investigated throughout this study. The constants in this study are beam dimensions and compressive strength for concrete. The effects of the shape, size and locations of opening on the torsional behaviour of deep beams under torsional loading are studied in the paper. The results showed the square opening is weakest due to the concentration effect which increases the stresses and the opening size participate main role in strength of deep without steel fiber. Also, the steel fibre in which the presence of steel fiber causes increasing in the torsion strength about (30-32) of tested specimens.

Experimental investigation on the mechanical behavior of hybrid bonded (rivet/adhesive) tubular lap joint (composite to metal) under pure torsion

The hybrid joints being used in the design of mechanical structures because of their significant advantages. The tubular lap joints are used widely in aerospace, naval, and transport industries such as rudder and elevator rods, driving shafts, pull push rods, anti-roll bar and stabilizer bar in cars, trucks and trains. The torsional behavior of mechanical, adhesively bonded, and hybrid tubular lap joints for aluminum to aluminum, and composite to aluminum subjected to pure torsion have been investigated experimentally. The effect of outer tube material and thickness, the joint’s type, and cured and post-cured temperature (room temperature and 40 °C), have been investigated experimentally. A fixture and a torsional set-up device have been designed and manufactured to apply the required torque to the joint. The outcomes from composite to aluminum joints confirm that the hybrid joint has 39.5% and 276.6% higher torque capacity than the mechanical joint and adhesively bonded joint, respectively. Furthermore, the cured and post-cured process at 40 °C, increased the maximum torque to failure, 37.6% and 57.1% for adhesively bonded and hybrid (rivet/bonded) joint, respectively. It has been observed that by upgrading the mechanical joint and adhesively bonded joint to the hybrid (rivet/bonded) joint, increasing the amount of joint’s strength and torque capacity in comparison with the increase in the weight of the structure is affordable.

Investigating the behavior of lightweight foamed concrete T-beams under torsion, shear, and flexure

Compared to conventional normal weight concrete, Lightweight Concrete (LWC) has significantly lower own-weight-to-strength ratio and good thermal insulation. Previous studies showed that the design codes underestimate the strength of LWC beams under pure shear force or pure torsion moment. In addition, the behavior and design of LWC T-beams under combined bending, shear and torsion was never investigated. Thus, this current study explores the effect of various parameters on the behavior of lightweight foamed concrete (LWFC) T-beams under combined shear, torsion and moment. Investigated parameters included the following: shear-span-to-depth ratio, torsion-to-shear-depth ratio, flange-to-web-width ratio, and transversal reinforcement ratio. An experimental program was conducted which included testing five T-beams under various ratios of combined loading. In addition, a numerical model was developed for LWFC T-beams under combined loading and verified using available experimental results. Moreover, a parametric study was performed to further investigate the effect of the selected parameters on the behavior of LWFC T-beams. Last but not least, the most recent internationally recognized design code is selected and used to calculate the T-beams strength, which was compared with the ones from the experimental and numerical investigations. For small values of the shear-span-to-depth ratio, the LWFC T-beams strength increased with the decrease of the torsion-to-shear-depth ratio compared to those with large values of the shear-span-to-depth ratio. In addition, the effect of the flange width was found to be insignificant. Moreover, the failure mode for beams with transversal reinforcement ratio above 1.2%, changed from under-reinforced mode to an over-reinforced one. Last but not least, the strength predicted using selected design code was found to be overly conservative compared to that experimentally measured and that numerically predicted for LWFC T-beams under combined loading.

Effect of concrete cover on the pure torsional behavior of reinforced concrete beams

Torsional behavior of RC members is dependent on various factors including the amount of rebar, concrete strength, member cross-section, depth to width ratio, and concrete cover. Although there is an enormous amount of knowledge on the effect of the above-mentioned factors on torsional behavior, studies pertaining to the effect of concrete cover is scarce. In the current study, a total of nine RC beams with clear concrete cover thickness ranging from 16 mm to 46 mm were experimentally investigated for pure torsion. Coupled with concrete cover depth, the effect of transverse reinforcement spacing and compressive strength of concrete were systematically investigated. Moreover, the experimental results were used to examine the prediction of commonly used codes including ACI, CSA, and Eurocode. To have a holistic view, the reliability of existing prediction graphical methods developed based on the well-known and accepted theories of MCFT and STM as well as recently developed empirical equations were also examined. The experimental results indicated the presence of relatively larger cover greatly affects both the ultimate capacity and overall torsional behavior of RC members. When compared with the experiments, ACI provides a highly conservative estimate, particularly with the increase of the cover depth. On the contrary, CSA and Eurocode provide unsafe predictions. Although the prediction is on the unsafe side, CSA and Eurocode gave a consistent prediction with smaller scatter for the different concrete depths. The prediction of the models based on the graphical methods and the empirical equation were also found to be unsafe with the effect becoming highly pronounced for cases with relatively large concrete cover. Overall, the experimental investigation showed the thickness of cover concrete has a significant effect on the pre and post-peak torsional behavior of RC members.

Seismic behaviour of concrete-filled steel tubular columns with internal H-section steel under pure torsion and compression–torsion loads

Concrete-filled steel tube (CFST) columns have been widely used in the construction industry because of their excellent compression capacity and torsion resistance. Regarding traditional CFST columns, the H-CFST column with an additional H-section steel member embedded in the core concrete provides improved fire and compression resistance. In this study, the seismic performance of nine H-CFST columns under cyclic torsional and compression–cyclic torsional loads was experimentally analysed. In the experiments, the failure mode, torque versus torsional angle hysteresis, torque versus torsional angle skeleton, torsional stiffness degradation, and energy dissipation capacity were determined. The hysteretic curves of the H-CFST columns under torsion were relatively plump in shape and exhibited no ‘pinching’ phenomenon, and the torsional stiffness of the H-CFST columns under unloading and reverse loading was approximately equal to the initial torsional stiffness. In addition, the applied compression had remarkable effects on the torsional capacity, torsional ductility, torsional stiffness, and hysteretic loop energy dissipation of the H-CFST columns. The shear capacities of the steel and concrete under normal stress or combined normal and shear stress were determined based on the latest theories and test results. Moreover, design method for the determination of the torsional capacity of H-CFST columns under compressive torsion is proposed based on the test results, and the theoretical contribution ratio of the H-section steel, steel tube, and concrete in the H-CFST columns to the torsional capacity was determined.

Investigation on the performance of a new pure torsional yielding damper

A new type of pure torsional yielding damper made from steel pipe is proposed and introduced. The damper uses a special mechanism to apply force and therefore applies pure torsion in the damper. Uniform distribution of the shear stress caused by pure torsion resulting in widespread yielding along pipe and consequently dissipating a large amount of energy. The behavior of the damper is investigated analytically and the governing relations are derived. To examine the performance of the proposed damper, four types of the damper are experimentally tested. The results of the tests show the behavior of the system as stable and satisfactory. The behavior characteristics include initial stiffness, yielding load, yielding deformation, and dissipated energy in a cycle of hysteretic behavior. The tests results were compared with the numerical analysis and the derived analytical relations outputs. The comparison shows an acceptable and precise approximation by the analytical outputs for estimation of the proposed damper behavior. Therefore, the relations may be applied to design the braced frame system equipped by the pure torsional yielding damper. An analytical model based on analytical relationships was developed and verified. This model can be used to simulate cyclic behavior of the proposed damper in the dynamic analysis of the structures equipped with the proposed damper. A numerical study was conducted on the performance of an assumed frame with/without proposed damper. Dynamic analysis of the assumed frames for seven earthquake records demonstrate that, equipping moment-resisting frames with the proposed dampers decreases the maximum story drift of these frames with an average reduction of about 50%.

Axial-torsion behavior of superelastic tubes: Part I, proportional isothermal experiments

The tensile response of superelastic shape memory alloys (SMAs) has been widely studied, but detailed experimental studies under multi-axial loading are relatively rare. In Part I, we present the isothermal responses of commercially-available superelastic NiTi tubes for a series of proportional stretch-twist controlled histories, spanning pure tension to simple torsion to pure compression. These axial-shear responses are used to quantify the onset and saturation during forward (loading) and reverse (unloading) stress-induced transformations for the first time. Each of the four transformation surfaces is well-captured by a smooth (three-parameter) ellipse in both strain and stress space. A simple Gibbs free energy model is presented to show how the driving force for phase transformation is approximately constant across all proportional strain paths and how the stress and strain transformation surfaces are conjugate to one another. In addition, transformation kinetics and surface strain morphologies are characterized by stereo digital image correlation (DIC). Under extension at low amounts of twist, stress-induced transformation involves strain localization in helical bands that evolve into axial propagation of ring-like transformation fronts with fine criss-crossing fingers (similar to those seen by Q. P. Sun and co-workers in pure extension). However, at large amounts of twist, including simple torsion and pure torsion, we report a new transformation morphology, involving strain localization along nearly longitudinal bands in the tube. The sequel (Part II) will address the response to non-proportional stretch-twist paths. Together, these detailed multi-axial results advance the scientific understanding of superelasticity and inform efforts to develop high-fidelity SMA constitutive models and simulation tools.

Behavior of RC Beams with Large Openings Subjected to Pure Torsion and Retrofitted by Steel or CFRP Plates

Torsion considered with an increasingly great importance by structural engineers. Some of the typical cases are space frames, spandrel beams, beams supporting balconies, eccentrically loaded beams, spiral staircases, horizontally curved beams, skew bridges, etc. Transverse openings, in Reinforced Concrete (RC) beams may be essential required for accommodating utility services in a building structure. Provision of an opening through a beam, however, changes its simple mode of behavior to a more complex one. Therefore, the design of such beams needs special treatment. Strengthening or retrofitting of concrete structures to compensate the presence of transverse opening not only depends on the applied material but also depends on the used technique. Carbon Fiber Reinforced Polymers (CFRP) plates, provide a more technical alternative to the traditional methods of strengthening in many cases as it gives high strength, low weight, corrosion resistance, easy and quick installation and less changes in structural geometry. An experimental test program of twenty-one RC beams with central large openings subjected to pure torsion were strengthened by using additional layers of externally bonded steel or CFRP plates with different techniques. The behaviors of the tested specimens were investigated and compared to identify the effectiveness of each method and material of strengthening to increase the torsional strength of beam with different opening sizes. The main conclusions and recommendations drawn from the study were discussed and summarized. The research shows that the methods of strengthening by using externally bonded steel strips fixed by eboxy and steel dowels and CFRP plates gave best results.

Fatigue life assessment of welded joints under sequences of bending and torsion loading blocks of different lengths

AbstractIn this work, the nominal stress concept, the notch stress approach and two critical plane approaches are used to analyse the fatigue endurance of a pipe‐to‐plate welded joint subjected to complex loading histories. Both the pipe and the plate were made of S355JR steel. Starting from already known fatigue endurance curves obtained for the same specimens under pure bending and pure torsion, a first series of tests was conducted, in which specimens were loaded in bending for a given fraction of the estimated life and then in torsion until failure. A similar series of tests was then carried out by changing the loading order: specimens were firstly loaded in torsion for a given fraction of the estimated endurance and then in bending until failure. The whole test campaign was repeated for two different fractions of the estimated life, that is, 0.3 and 0.45, respectively. After that, additional three series of tests were carried out, in which the specimens were subjected to consecutive sequences of bending and torsion blocks of different lengths (short, medium and long, respectively); the relative length of the bending and torsion block in each series was determined in order to produce the same damage. The experimental results, in terms of total damage at failure, were analysed using the Palmgren–Miner hypothesis. For all the assessment methods, the characteristic endurance curves were firstly calibrated on the basis of finite element (FE) analyses and of the experimental results obtained under pure bending and pure torsion loadings. The observed damage at failure resulted always greater than 0.5 for all the employed methods and greater than 1 for most of the tests. The different methods gave similar results, with the critical plane methods giving a slightly more stable damage at failure and a correct determination of the failure location. For all the methods, the damage at failure slightly reduces as the block length shortens.

Theoretical and Experimental Investigation on Mechanical Behavior of Aluminum to Aluminum Tubular Bonded Lap Joint under Pure Torsion and a Finite Element Comparison with Hybrid Rivet/Bonded Joint

The combination of mechanical and bonded joints creates a new connection type, called hybrid joint which has the benefits of both mechanical and bonded joints. In this research, the mechanical behavior of the tubular bonded lap joint between aluminum tubes subjected to pure torsion has been investigated experimentally and numerically, and the results have been compared. The mechanical behavior of the hybrid (rivet/bonded) joint has been investigated numerically and the outcomes have been compared. The adhesive and rivets have cohesive elements and bushing connector elements, respectively. The results from the hybrid joints and the damage mechanism show that the rivets change the interface shear stress and the stress distribution of the joint, and affect the joint’s torque capacity and strengths. It has been observed that for specimens with overlap lengths close to effective length, the hybrid joint is more effective.

Combined compression-bending-torsion behaviour of CFST columns confined by CFRP for marine structures

An innovative composite structural member formed by concrete filled steel tube (CFST) circumferentially confined by carbon fiber-reinforced plastics (CFRP), i.e., referred to as CFRP-CFST, has great potential to be used in marine environment due to its excellent structural performance and corrosion resistance. This paper aims to investigate the behaviour of CFRP-CFST subjected to combined compression-bending-torsion load. Quasi-static tests are conducted on 5 CFRP-CFST members and 3 reference bare CFSTs. The test parameters include the loading scenario (pure torsion, bending-torsion, and compression-bending-torsion), the axial load ratio and the layers of CFRP wrapping. Experimental results show that the CFRP-CFST members exhibit good energy dissipation capacity under pure torsion and compression-bending-torsion loads, while the applied axial force benefits the bearing capacity and the stiffness. However, ‘pinch’ effect is observed in the load-deformation hysteretic curves of CFRP-CFST under bending-torsion load. It indicates that the confinement provided by CFRP can significantly improve the column bearing capacity and ductility under torsion. When subjected to combined compression-bending-torsion, the CFRP wrapping can effectively improve the column ductility. The energy dissipation capacity increases with multiple CFRP layers. Eventually, the structural mechanism at the ultimate limit state is analyzed, with the calculation methods for the bearing capacities evaluated.

Latent hardening/softening behavior in tension and torsion combined loadings of single crystal FCC micropillars

In metallic materials, the activation of one slip system increases the flow strength of other slip systems, which is phenomenon known as latent hardening. This latent hardening behavior has been understood by the “forest hardening” mechanism arising from mutual dislocation interactions at the continuum length scale. As the size of a sample decreases to the submicron scale, the interactions between dislocations become increasingly sparse, so plastic deformation is instead governed mainly by dislocation sources. In this paper, we use three-dimensional dislocation dynamics (DD) simulations to examine plastic deformation in single crystalline Cu micropillars subjected to two types of combined loading conditions: tension after torsion and torsion after tension. These combined loadings are then compared with simple tension and pure torsion, respectively. We find that there exists a transition from latent hardening to latent softening in 600 nm samples undergoing tension after torsion. The systematic computational and theoretical model described here suggests explosive multiplication causes dislocation density to greatly increase, giving rise to latent softening in those micropillars under tension after torsion.

Experimental and numerical study on the nonlinear performance of single-box multi-cell composite box-girder with corrugated steel webs under pure torsion

Currently, an increasing number of single-box multi-cell composite box-girders with corrugated steel webs (SBMC-CBGCSWs) have been built in China and Japan. However, the torsional stiffness of SBMC-CBGCSW is dramatically decreased due to the employment of thin corrugated steel webs (CSWs). Investigations of SBMC-CBGCSW under pure torsion are relatively limited, therefore, additional research is needed to investigated to guarantee the safety of such bridges. In this paper, an experimental study on four scaled specimens subjected to pure torsion is conducted to understand the effect of the number of cells and spacing of CSWs on the full torsional response of SBMC-CBGCSW. The failure mode, cracking patterns, and buckling patterns of specimens are presented, and a new shear strain relationship between CSWs obtained from experimental results is proposed to evaluate the contribution of inner CSWs to the torsional behavior of SBMC-CBGCSW. Then, finite element analysis (FEA) models are created to compare with experimental results, such as torque-twist curves, shear strains of CSWs and shear strains of concrete slabs. Finally, a parametric study is performed to examine the effect of geometric factors, such as the ratio of width to height, ratio of width to span length, ratio of width to thickness of slab, number of cells and spacing of CSWs, on such bridges under torsion.

Modern and future schemes of very-high cycle fatigue tests

The development of a new piezoelectric fatigue machine operating in pure torsion is presented in this paper. The proposal for implementation of a testing machine to research on very-high cycle fatigue at biaxial bending is studied. Results of pure torsion tests on titanium alloy VT3-1 processed by forging and extrusion are shown. Evaluations of specimens shapes made of aluminum alloy D16T and titanium alloy VT3-1 were conducted as well as the possibility to conduct VHCF bi-axial bending tests was confirmed.

Saint Venant’s torsion of homogeneous and composite bars by the finite volume method

We propose a new finite-volume based approach to the solution of Saint Venant’s torsion problems of homogeneous and composite prismatic bars subjected to pure torsion. The semi-inverse approach is employed to construct an approximate displacement field characteristic of pure torsion within the subvolumes of the beam’s discretized cross section such that the governing differential equation for the warping function is locally satisfied in each subvolume in an integral sense. Orthotropic subvolumes are admitted in the formulation to enable analysis of bars comprised of heterogeneous microstructures, including composite materials with orthotropic shear moduli. Continuity of both displacements and tractions across subvolumes’ interfaces is satisfied in a surface-average sense, together with traction-free lateral boundary conditions. Closed-form expressions for the stiffness matrix elements that relate surface-averaged displacements to tractions are provided for ease of programming. The convergence and accuracy of the proposed method are assessed and verified upon comparison with the exact elasticity solutions for prismatic homogeneous and composite bars of rectangular cross section and the corresponding finite-difference solution for the homogeneous bar. The utility of the developed solution methodology is first illustrated by analyzing torsion of homogeneous T and box beams, focusing on the singular behavior at the re-entrant corners and the concomitant membrane analogy’s applicability. Then, composite cross sections reinforced by angle braces as well as continuous fiber-reinforced wraps with graded shear moduli are investigated with the aim of mitigating the re-entrant corner shear stress singularities, not easily analyzed using the finite-element or finite-difference approaches.

Numerical study on the axial-torsional response of an unbonded flexible riser with damaged tensile armor wires

The local mechanical response of a 2.5" unbonded flexible riser with damaged wires is studied by a nonlinear finite element (FE) model. Firstly, the riser was supposed to be under pure tension and pure torsion. Stiffness and force distribution of the intact riser predicted by the analytical and numerical models are compared, and deviations between the two solutions are discussed. Then, two up to eight wires in the outer tensile armor layer are assumed to be damaged. Numerical results indicate that uneven deformations caused by the broken wires result in a clear nonlinear force redistribution among the outer wires. The maximum and minimum forces supported by the remaining intact outer wires are closely related to the number of damaged wires, boundary conditions and the load direction. Finally, the effect of internal frictions on the load recovery of damaged wires is studied by increasing the FE model length and applying the pre-pressure. It was found that damaged wires can progressively recover their load-carrying capacities with the increase of internal frictions. In addition to the boundary effects, axial stress of the damaged wire is linear with the length of the riser, which indicates that results obtained from the short model can be employed to estimate the load recovery characteristics of the long model.