External Axial Load Research Articles

Advantages of using DIC for capturing mechanical shear sliding behaviour of the FRCM strengthened masonry

This paper aims to analyse the advantages of using Digital Image Correlation (DIC) method to capture the effects of the FRCM on masonry wall shear failure. In the scientific literature, most of the experimental programs is focused on strengthening against flexural failure by means of bending tests and against shear, diagonal cracking, by means of diagonal compression tests. The shear failures are one of the main failure modes for the in-plane behaviour of masonry walls in case of horizontal loads. This study primarily focuses on experimentally determining the capacity of clay brick masonry under sliding shear loads for different normal stress levels with a standard test method. The assessment of shear capacity is based on a Mohr-Coulomb failure criterion depending on the external axial load, the internal friction angle and the cohesion values for unreinforced masonry. The experimental tests have been carried out on both unreinforced and strengthened specimens. The results of the tests demonstrate that FRCM, despite the reduced anchorage length in the tests, can significantly enhance the structural performance of masonry structures for sliding shear failure mode. In addition, DIC method is used to analyse, in greater detail, the cracks and the strain evolution in order to analyse the failure of specimens.

Non-linear analysis of rectangular cross-sections with different reinforcements: dimensionless closed form solution

This paper presents an algorithm to solve a non-linear rectangular cross-section analysis by means of closed form equations. The equations are provided in a dimensionless form in order to provide generalizable results. The algorithm is based on the direct integration of the non-linear constitutive behaviour of the materials into the stress-block constitutive behaviour. The algorithm is based on masonry rectangular cross-sections characterized by an external axial load similar to Reinforced-Concrete cross-sections. The failure of the strengthening system and the masonry are analysed in the proposed algorithm, in an unconventional manner, analysing the behaviour even after the attainment of the ultimate strains, accounting for progressive damage. The algorithm allows to prevent the cross-section fiber analysis and the consequential iterative procedure to retrieve the neutral axis depth. Furthermore, the direct integration allows to evaluate the exact solution of the problem without numerical approximations. The results are discussed by means of several parametric analyses in terms of P–M domains and bending moment–curvature diagrams in dimensionless form. The proposed approach aims to simplify the cross-section analysis process in complex algorithms as in the risk analysis based on a large scale approach, where a large number of structures and structural members are analysed in the vulnerability process.

Numerical and analytical models of the mechanism of torque and axial load transmission in a shock absorber for drilling oil, gas and geothermal wells

The paper proposes an improved design of a shock absorber used in drilling deep oil and gas and geothermal wells with polycrystalline diamond compact (PDC) bits. The proposed innovations successfully combat the dangerous phenomenon of self-excited vibrations, which can lead to malfunctions such as stick-slip and whirling of the drilling tool. Most conventional drill shock absorbers are designed to only absorb longitudinal vibrations, which was sufficient when using roller cutter bits for the drilling process. However, the design features of PDC bits and the phenomenon of interaction of their cutters with interlayered rocks during deep drilling impose new requirements on the properties of the drill shock absorber. To protect the downhole tool from abnormal torque values and torque oscillations, it is proposed to equip the shock absorber with a special torque transmission unit in the form of a fourteen-thread self-releasing screw pair. This unit is capable of transforming increases in external torque into increases in the force that loads the elastic element of the shock absorber. The numerical and analytical models of the mechanism of transferring external axial load and torque to the elastic element of the drill shock absorber are constructed. The distribution of contact pressures on the interacting surfaces of the screw pair and the distribution of equivalent stresses in the screw pair parts are analysed. The strength of the proposed drill shock absorber assembly was evaluated using the Huber-von Mises energy criterion. The dependence of the load transmitted to the elastic element of the shock absorber on changes in the external torque and external axial force is investigated. In general, it is determined that the external load is distributed evenly between all turns of the screw pair, and the limit state of the parts of the proposed assembly is not reached even under high-torque operating load. The obtained analytical dependencies will allow to effectively determine the required strength and stiffness of the elastic element of the drill shock absorber at the design stage. The obtained analytical results were verified using a finite element model.

Geometrically Nonlinear Buckling of FG-CNTRC Plates Stiffened by FG-CNTRC Stiffeners Subjected to Combined Loads Using Nonlinear Reddy’s HSDT

The nonlinear buckling and postbuckling of functionally graded carbon nanotube reinforcement composite (FG-CNTRC) plates resting on the nonlinear effect of elastic foundation under combined load including external pressure and axial compression loads with uniformly distributed temperature rises are fully investigated in this paper. The FG-CNTRC plates are reinforced by FG-CNTRC stiffeners and the plate-foundation interaction is modeled using a nonlinear model. The higher-order shear deformation plate theory with the geometrical nonlinearities of von Kármán is applied to establish the basic formulations. Additionally, by using the anisotropic higher-order shear deformation beam theory, a new smeared stiffener technique is successfully developed for FG-CNTRC stiffeners. Galerkin’s method is used to achieve the equilibrium equation system in the nonlinear algebraic forms, and the critical load and postbuckling load–deflection curve expression are explicitly determined. The numerical investigations discuss the influences of FG-CNTRC stiffeners, hardening/softening nonlinear elastic foundation, uniformly distributed temperature rises, geometrical and material features on nonlinear stability of stiffened FG-CNTRC plates.

Component test of nickel-based alloys and their welded joints under long-term creep loading

The aim of the paper is to investigate experimentally the creep behavior of improved materials and welded joints at component scale under near-to-service operating conditions, which are promising for the application in highly efficient and flexible future power plants.It focusses on the creep behavior under multiaxial loading of similar and dissimilar welded joints of high temperature resistant nickel-based alloys (A740H, A617B and HR6W) in the temperature range between 650 °C and 750 °C by means of thick-walled-component tests. In this case, the temperature, the external axial load and the internal pressure remain constant during testing.Numerical simulations are used for the estimation of the component axial load in order to induce a meaningful damage evolution without causing a total component failure. The metallographic investigation on the welds A740H/A740H and A617B/A740H indicated no test-related damage. Small cracks in circumferential direction were found on the welds HR6W/HR6W and HR6W/A617B after having reaching 2% local creep strain. The damage mechanism could be classified as a typical creep damage with carbides formation in the grain boundaries and thus grain boundary separations occur, which ultimately lead to the crack formation.In general, the FEM calculation underestimates the axial creep strain on the investigated welds, especially the initial creep strain evolution is not accurately predicted. However, the long-term creep strain evolution could be well predicted by FEM. In this case, the material parameters for the creep law should be further optimized in order to minimize the underestimation.

Проектный анализ подкрепленной композитной оболочки

The paper formulates the design calculation problem of a reinforced composite shell as a related problem of two shells — the layered and the lattice (ribbed). The layered shell is formed by a single double-helical monolayer; the lattice shell is made up of longitudinal and transverse ribs. The reinforced shell continuum model is based on a stiffness matrix equal to the sum of stiffness matrices of the quasi-homogeneous layered and ribbed shells, which are rigidly connected to each other and are deformed without slipping. External axial load between the two shells is distributed under the static conditions. The shells’ thickness is determined from the strength condition. The layered skin winding angle is found through iterations in achieving the goal function, for example, the minimum mass of a structure. The ribs transverse dimensions are found from the strength condition with preliminary setting of one of the ribs’ parameters. The obtained relationships make it possible to determine the stress-strain state of reinforced composite cylindrical shells.

Loading rate effect on mixed-mode I + II fracture of V-notched Brazilian disc rock specimen under impact loads

Dynamic failure processes of rock masses containing numerous discontinuities including pores, cracks and notches have been the major issues in structural safeties of underground buildings subjected to impact loads, such as earthquake, blast and vehicle vibration. At present, most of the studies are focused on the dynamic fracture behaviors of rocks containing crack-like defects, while the studies on rocks containing notch-type defects are very rare, especially under mixed-mode loading conditions. This paper aims to study the effects of loading rate on mixed-mode I + II fracture characteristics of flattened V-notched Brazilian disc rock specimen under impact loads by means of an split Hopkinson pressure bar (SHPB) system combined with a high-speed camera. Dynamic fracture tests were performed on a total of 125 groups of V-notched rock specimens with different notch angles (0°, 30°, 45°, 60°, and 90°) and loading angles (0°, 30°, 45°, 60°, and 90°) at different air pressures (0.16 MPa, 0.18 MPa, 0.20 MPa, 0.22 MPa, and 0.24 MPa). Based on dimensional analysis, a numerical method was proposed to establish the relationship between mixed-mode notch stress intensity factor (NSIF) at the V-notch tip and external axial load. The dynamic notch fracture toughness values of flattened V-notched Brazilian disc rock specimens were calculated from the maximum values of dynamic force in the SHPB tests according to the proposed numerical method. The effects of loading rate, notch angle, and loading angle on the mixed-mode I + II notch fracture toughness value and crack initiation angle were quantitatively analyzed, which were verified using a modified maximum tangential stress (MTS) criterion by considering the loading rate effect. It is found that the loading rate has a significantly positive effect on the notch fracture toughness value, but has a negative effect on the crack initiation angle due to the inertial effect under dynamic impact loads. Generally, pure mode I fracture occurs for the loading angle of 0° or 90°, pure mode II fracture occurs for the loading angle varying from 35° to 45°, and mixed-mode fracture occurs for other loading angles. Good consistencies of the mixed-mode I + II notch fracture toughness values and crack initiation angles of the V-notched rock specimens are observed between the modified MTS criterion prediction and experimental results. This work may improve the understanding of the dynamic fracture behaviors of rock masses containing notch-type defects during tunnel excavation and underground construction process.

Total hip arthroplasty monobloc stem neck rupture in patient with massive heterotopic ossifications: a case report and literature review.

Fractures of the femoral stem neck are a rare complication in hip prosthetic surgery, especially in non-modular components. The authors report a case associated with massive heterotopic ossifications, with the purpose to analyze risk factors and specific characteristics. A case of femoral monobloc stem neck rupture is described. A non-systematic literature review regarding risk factors for femoral stem neck fracture was conducted in the PubMed database. We report the case of a 61-year-old male who underwent surgery to remove calcifications four years after THA. Four months later the patient reported acute pain in the left hip, arising after a combined movement of external rotation and axial load while standing on the left foot, in the absence of any prodromic symptom. On radiographs, a displaced fracture of the neck of the hip prosthesis was revealed, together with massive heterotopic ossifications. After THA revision the patient's symptoms were resolved. Prosthetic femoral neck fractures are a rare complication. We suggest that this case represents a unique type of fatigue rupture, where neck length and the presence of massive heterotopic calcifications contributed to flexion forces, resulting in failure in the midpoint of the neck.

Calculation method for the static carrying curve of double-row different-diameter ball slewing bearings.

A method for calculating the static carrying curve of a double-row different-diameter ball slewing bearing was proposed. The relationship between the internal maximum rolling element load of each row and the combined external axial load and tilting moment load of the slewing bearing was established using the deformation compatibility and force equilibrium conditions. The rolling element load distribution range parameters of the main and auxiliary raceways of the double-row different-diameter ball slewing bearing were used as input invariables, and the corresponding external load combinations of the axial and tilting moment loads of the slewing bearing were obtained. These external load combinations were plotted in the coordinate system to obtain the static carrying curve of the slewing bearing. The obtained static carrying curve was compared with that calculated using the finite element method for verification. Finally, the influences of detailed design parameters such as the raceway groove radius coefficient, raceway contact angle, and rolling element diameter on the carrying capacity of the double-row different-diameter ball slewing bearing were analyzed based on the carrying curves. As the groove radius coefficient increases from 0.515 to 0.530, or the contact angle increases from 50° to 65°, the carrying capacity of the slewing bearing decreases. As the rolling element diameter increases from 0.90 times the initial diameter to 1.05 times the initial diameter, the carrying capacity of the slewing bearing increases.

Revisiting the Role of Knee External Rotation in Non-Contact ACL Mechanism of Injury

An anterior cruciate ligament (ACL) tear is a severe sports injury that often occurs in young athletes. Besides the strong cumulative evidence on noncontact ACL tears, the injury mechanism (especially the contribution of external rotation) is still not well understood. The present work aims to evaluate which knee kinetics result in higher ACL stress and strain. A finite element model of the ACL was developed with a detailed geometry; the two distinct bundles (anteromedial and posterolateral) and the surrounding connective tissue were modelled based on medical anatomic measures and images. The model was validated using computational and cadaveric external data. Sixteen simulations were performed using different combinations of moments and axial loads applied to the knee model as boundary conditions. The results demonstrated that the peak stress (11.00 MPa) and strain (0.048) occurred at the midportion of the anteromedial bundle with the higher values being obtained under a combined knee valgus, flexion, tibial external rotation and high axial load. Anterior load showed low sensitivity in ACL stress and strain peaks. The tibial external rotation showed a higher contribution to the peak ACL stress and strain as compared to internal rotation. These results reinforce the role of axial load and highlight the importance of external rotation on ACL stress and strain, which may be suggestive of the ACL tear mechanism. The role of external rotation is often neglected and should be further explored in future cadaveric and experimental studies. The findings of this study provide data-driven insights to optimize the indications for prevention, diagnosis and treatment of ACL injuries in clinical practice and contribute to raising awareness of the injury mechanism among all relevant stakeholders.

Difference in Joint Stability Between Small Posterior Malleolar Fragments With Fixation and Those Without Fixation: A Biomechanical Cadaver Study

The indication for the surgical treatment of ankle fractures that involve a posterior malleolar fragment remains controversial. This cadaver study assessed the biomechanical results of rotation stiffness of Haraguchi type 1 posterior malleolar fragments with or without cannulated screw fixation. Twelve anatomic lower-extremity specimens from 6 cadavers were tested. Six right legs were subjected to posterior malleolus osteotomy (Haraguchi type I) followed with (group A; n=3) or without (group B; n=3) fixation using a cannulated screw. Ankle joint stability was measured under both external rotation force and axial loading, and the passive resistive torque was measured in both groups. The mean torque value in group A was 0.1093 Nm/º, while that in group B was 0.0537 Nm/º. There was a significant intergroup difference (p=.004). In group B, the torque value was further increased in the latter rotation period (about 40-60 degrees). Group A proved more stable under experimental conditions than group B. Fixation in type I posterior malleolar fragments produced improved stability in ankle rotation, even for posterior malleolar fragments involving <25% of the articular surface, and has been considered an effective aid in treatment.

Ultimate local strength of a submarine structure considering the influence of localized reduction of thickness

Commonly, failures that occur in a submarine's structure could be caused by the high external hydrostatic pressure which may first take it to an unstable condition influenced by its geometry. In these vessels, reduction of thickness can develop because of corrosion or similar causes, which leads to reduction of structure's strength. The objective of this work is to determine the ultimate load that a cylindrical part of a submarine structure can support, considering the influence of localized thickness reduction. For this purpose, firstly the ultimate response of a 50 cm steel square plate of 3 mm in thickness, intact and considering local thickness reduction was analyzed using experimental tests and numerical approach. Then, the ultimate response of a high strength steel cylinder is numerically analyzed, intact condition and with localized thickness reduction. For this analysis typical submarine hull segment including three circular frames is modelled with solid finite elements subjected to external pressure and axial load, simultaneously. Buckling occurs in the elastic range of the material and the circular plate thickness reduction considering a diameter of 78% of the space between frames and 30% of the thickness, reduces only in 6% the collapse external load on the cylinder.

Bifurcation analysis of residually stressed neo-Hookean and Ogden electroelastic tubes.

The conditions for bifurcation of a circular cylindrical tube of elastic material subjected to combined axial loading and internal pressure are well known and are frequently used as a reference in related works. The present paper takes the theory further by considering a residually stressed circular cylindrical dielectric tube subjected to a combination of internal or external pressure, axial load and radial electric field. We examine axisymmetric incremental deformations and increments in the electric displacement superimposed on a known finitely deformed and residually stressed configuration in the presence of an electric field. The governing equations and boundary conditions are first obtained in general form and then specialized for the neo-Hookean and Ogden electroelastic models. The system of equations is solved numerically for different values of charge density and radial and circumferential residual stresses, and the results are compared with the purely elastic case. The bifurcation curves are presented as the azimuthal stretch on the inner surface versus the axial stretch together with the corresponding zero pressure curves. This article is part of the theme issue 'The Ogden model of rubber mechanics: Fifty years of impact on nonlinear elasticity'.

The influence of the Gaussian curvature sign of the compound shell structure’s middle surface on local and overall buckling under combined loading

The buckling problem of an elastic compound shell structure with a variable Gaussian curvature of the middle surface, especially the middle surface meridian curvature sign, under the action of external pressure and axial loading is considered. In continuation of the previous research of the authors, this paper is devoted, in particular, to examining the influence of the negative Gaussian curvature sign of one of its compartments on stability. The solution is based on using the method of finite differences for basic stability equations of each compartment in the case when one of them can have a negative curvature of the meridian, taking into account the discreteness of the intermediate rib location and their rigidity from the initial curvature plane as well. The obtained solution allows visualizing the buckling modes under various combinations of external loading and identifying rational, according to overall buckling modes, geometric and rigidity parameters of the system being investigated.

Nonlinear buckling of higher-order shear deformable stiffened FG-GRC laminated plates with nonlinear elastic foundation subjected to combined loads

The nonlinear postbuckling analysis of functionally graded graphene reinforced composite (FG-GRC) plates taking into account the nonlinear effect of elastic foundation subjected to external pressure and axial compression load in thermal environment is analytically examined in this paper. Assuming that the FG-GRC laminated plates are stiffened by FG-GRC laminated stiffener system resting on a three-parameter nonlinear elastic foundation. The higher-order shear deformation plate theory (HSDPT) with the geometrical nonlinearities of von Kármán is applied to establish the basic formulations. Moreover, the smeared stiffener technique is successfully improved for the higher-order shear deformable anisotropic stiffener system by using a homogeneous model of the laminated beam. Galerkin's method is used to achieve the expressions of critical buckling loads and postbuckling load-deflection curves in explicit form. The numerical values display the influences of nonlinear elastic foundation, temperature, laminated stiffeners, material, and geometrical features on nonlinear responses of plates.

Influence of microwave irradiation on the permeability of coal with different bedding dip angles

Microwave irradiation (MI) is a prospective method for increasing CBM production. Due to the permeability anisotropy caused by bedding structural plane, the spatial relationship between underground microwave irradiation drillings (MID) and the coal bedding plane has become an important factor affecting the effect of MI on enhancing production. The self-developed MI device numberer WY3S02 was used to carry out the MI experiment on samples with different bedding angles (BDA). The permeability of coal before and after MI was tested by the steady-state seepage method. The surface temperature and ultrasonic data of samples during the test were collected, and the influence of MI on the permeability of coal with different BDA was studied. The experiments indicate that the permeability of samples with different BDA increases by 30.2–100.1 times after MI under external axial load, and the increase of permeability is positively correlated with the BDA. The permeability after MI shows the variation law of K (90°) > K (60°) ≥ K (45°) > K (30°) > K (0°), showing an obvious bedding effect. The standard deviation of the lateral surface temperature of the specimen increases with the increase of the BDA, which makes the thermal fracture degree of the sample with large BDA higher, resulting in more dominant seepage channels, which is manifested as greater permeability growth. These results provide a scientific basis for the design of MID in the method of enhanced coalbed methane by microwave irradiation (MI-ECBM).

Graphyne nano-spirals under tension: Effects of base structures on superelasticity and fracture mechanisms

With advances in nanotechnology, two-dimensional nanostructures have shown great promise for a wide range of applications. Of particular interest is their spiral forms as essential components of nanoelectromechanical systems. In this paper, the mechanical behavior of the spirals made of different graphyne structures under tension is investigated using molecular dynamics simulation and the results are compared with graphene nano-spirals. Inspired from the conventional macroscale springs with various cross-sections that have different behaviors against the external axial loads, we comprehensively analyze the effects of various base structures on superelastic deformation capabilities and fracture mechanisms of the nano-spirals. In general, five distinct deformation stages corresponding to van der Waals nonbonding interaction and covalent bonding are observed in the force-strain diagrams. Moreover, the effects of inner and outer radii on the mechanical characteristics are examined. It is found that the stretchability of nano-spirals increases up to a maximum threshold as the outer radius increases, then decreases with its further increase. This decrease is seen more clearly in spirals made of graphene and γ-graphyne while α- and β-graphyne nano-spirals outperform in larger widths. Hence, we show that deliberate manipulation of the base structures can significantly extend the applicability of nano-spirals to larger widths.

Supercritical nonlinear transverse vibration of a hyperelastic beam under harmonic axial loading

Dynamics of a hyperelastic beam in a buckled state subjected to a harmonic axial load is investigated in this work. For the static case, the buckled configuration of the hyperelastic beam is first determined through an asymptotic method when the axial load is in excess of its critical load. Then, the governing equation of vibration of the buckled beam is derived, which is a complex nonlinear partial differential equation with varying coefficients. The first natural frequency of the buckled beam is obtained by linear analysis and effects of material and geometrical parameters on it are numerically investigated. By applying the Galerkin method, the governing equation for nonlinear transverse vibration of the beam in the buckled state is transformed into a series of strongly nonlinear ordinary differential equations. Dynamic characteristics of the hyperelastic beam are investigated by the Runge–Kutta method. Bifurcation diagrams, time traces, phase-plane portraits, and Poincare sections are obtained for different values of the external excitation frequency and amplitude of variation of the axial load. Results show that different dynamic behaviors of the hyperelastic buckled beam such as periodic, multi-periodic, quasiperiodic, and chaotic motions can be found when the amplitude of the axial load is varied. Amplitude–frequency responses of the hyperelastic buckled beam are obtained by the Runge–Kutta method and harmonic balance method. Results from the Runge–Kutta method are in good agreement with those from the harmonic balance method. Lastly, effects of the external mean axial load, amplitude of variation of the axial load, geometrical and material parameters on amplitude–frequency responses of the buckled beam are numerically investigated.

Experiments on buckling behavior of thin-walled steel pipes subjected to axial compression and external pressure

Pipelines are exposed to various forces in order to develop relative compressive axial and external pressure load in some cases of fluid transmission. An experimental study was conducted to investigate the buckling behavior of thin-walled steel pipes when subjected to a combination of axial compression preloading and external pressure. In addition, the response of some specimens was separately investigated subjected to pure external pressure and axial compression load. A significant reduction was observed in the buckling load and the post-buckling capacity of the thin-walled pipes with increasing the value of axial compression preloading. The existing analytical models for predicting the buckling load of the pipelines were modified. The numerical models were developed and verified using the experimental results, and interaction between the axial load and external pressure was graphically demonstrated for different geometrical ratios.

Unified fatigue life prediction of bolts with different sizes and lengths under various axial loading conditions

Bolts tend to show different fatigue behavior with respect to the size or shape of a bolt and the level of preload though it is the same material. This makes it difficult to predict the fatigue life of bolts. In this study, a novel method to construct a unified stress-life (S-N) curve was proposed for the three different bolts with different sizes and lengths subjected to various external axial loading conditions and preloads, ranging from 44 % to 88% of the ultimate tensile stress. A total of 133 experiments for 46 different fatigue conditions were conducted and finite element analysis was also performed to calculate multiaxial stress components at the root of the thread. The fatigue characteristics of the bolts were investigated depending on various loading conditions, and the life prediction performance with fitted S-N curves was compared with respect to four mean stress correction models. The unified S-N curve showed high accuracy in life prediction; 15 % mean absolute error without exceeding ± 50 % for finite life loading conditions.