Axial Compressive Stiffness Research Articles

Compression responses of composite corrugated sandwich square tube: Experimental and numerical investigation

By means of re-bonding inner square tube, corrugated core and outer square tube produced by hot pressing molding method, the composite corrugated sandwich square tubes (CCSSTs) were manufactured. Axial and lateral compression experiments were carried out on CCSSTs with length of 50 mm and 25 mm respectively, and the mechanical responses such as load, displacement and mid-height strain during the loading process were measured. The composite progressive damage finite element models were used to simulate the compression failure processes of CCSSTs. The simulated failure modes and load–displacement curves were in good agreement with experimental results. An analytical model based on homogenization theory was provided to evaluate the regularity of axial and lateral compression stiffnesses of CCSSTs. The research showed that the CCSST mainly underwent face crushing, face debonding and local buckling under axial compression. The lateral compression bearing capacity of CCSST reduced mainly caused by the outer face debonding. Increasing the height of the core could improve the axial compression stiffness and specific axial compression stiffness. The lateral compression stiffness performance and light weight benefit were both satisfying when the corrugation angle reaches 90°.

Time and temperature sensitivity of the hybrid III lumbar spine

Objective Researchers have found a variety of uses for the Hybrid III (HIII) dummy that fall beyond the scope of its original purpose as an automotive crash test dummy. Some of these expanded roles for the HIII introduce situations that were not envisioned in the dummy’s original design parameters, such as a relatively rapid succession of tests or outdoor testing scenarios where temperature is not easily controlled. This study investigates how the axial compressive stiffness of the HIII lumbar spine component is affected by the duration of the time interval between tests. Further, it measures the effect of temperature on the compressive stiffness of the lumbar spine through a range of temperatures relevant to indoor and outdoor testing. Methods High-rate axial compression tests were run on a 50th percentile male HIII lumbar component in a materials testing machine. To characterize the effects of tests recovery intervals, between-test recovery was varied from 2 hours to 1 minute. To quantify temperature effects, environmental temperature conditions of 12.5°, 25°, and 37.5 °C were tested. Results During repeated compressive loading, the force levels decreased consistently across long and short rest intervals. Even after 2 hours of rest between tests, full viscoelastic recovery was not observed. Temperature effects were pronounced, resulting in compressive force differences of 261% over the range of 12.5° to 37.5 °C. Compared to the stiffness of the lumbar at 25 °C, the stiffness at 37.5 °C fell by 40%; at 12.5 °C, the stiffness more than doubled, increasing by 115%. Conclusions A modest decrease in temperature can be sufficient to dramatically change the response and repeatability of the lumbar HIII component in compressive loading. The large magnitude of the temperature effect has severe implications in its ability to overwhelm the contributions of targeted test variables. These findings highlight the importance of controlling, monitoring and reporting temperature conditions during HIII testing, even in indoor laboratory environments.

Annular Defects Impair the Mechanical Stability of the Intervertebral Disc.

A biomechanical study. The purpose of this study was to investigate the effects of cruciform and square incisions of annulus fibrosus (AF) on the mechanical stability of bovine intervertebral disc (IVD) in multiple degrees of freedom. Eight bovine caudal IVD motion segments (bone-disc-bone) were obtained from the local abattoir. Cruciform and square incisions were made at the right side of the specimen's annulus using a surgical scalpel. Biomechanical testing of three-dimensional 6 degrees of freedom was then performed on the bovine caudal motion segments using the mechanical testing and simulation (MTS) machine. Force, displacement, torque and angle were recorded synchronously by the MTS system. P value <.05 was considered statistically significant. Cruciform and square incisions of the AF reduced both axial compressive and torsional stiffness of the IVD and were significantly lower than those of the intact specimens (P < .01). Left-side axial torsional stiffness of the cruciform incision was significantly higher than a square incision (P < .01). Neither incision methods impacted flexional-extensional stiffness or lateral-bending stiffness. The cruciform and square incisions of the AF obviously reduced axial compression and axial rotation, but they did not change the flexion-extension and lateral-bending stiffness of the bovine caudal IVD. This mechanical study will be meaningful for the development of new approaches to AF repair and the rehabilitation of the patients after receiving discectomy.

Study on axial compressive stiffness of RAC-encased RACFST composite columns

Twenty four specimens were designed to investigate the axial compressive stiffness of the recycled aggregate concrete(RAC)-encased recycled aggregate concrete-filled steel tube (RACFST) composite columns. The working mechanism of the RAC-encased RACFST composite column was investigated and the full range load–displacement curves of the composite columns were obtained. The interaction of each component of the composite column, i.e. the effect of the outer RAC from the stirrup and the steel tube, and the effect of the core RAC from the stirrup and the steel tube, were analyzed. The constitutive models of the outer unconfined RAC, the outer confined RAC, the core RAC were discussed. Thereupon, simple formulas were proposed to calculate the axial compressive stiffness of composite columns. These formulas can assist engineers to predict the axial deformation of structure in high-rise buildings more accurately.

Numerical analysis of axial compressive behavior of RC short columns subjected to non-uniform fire: A meso-scale study

The bearing capacity and durability of reinforced concrete (RC) structures can be affected by fire. In this study, a three-dimensional (3D) meso-scale simulation model for RC short column subjected to axial compression after exposure to fire was established. The degradation effect of mechanical properties of steel bars and concrete materials after high temperature was taken into account. The bond-slip behavior between longitudinal steel bars and concrete was also considered in the model. Based on the present simulation method, the failure mode and failure mechanism of the RC short columns were investigated. Moreover, the effects of fire scenario and fire duration on the axial compression performance of RC short columns were further investigated. It is found that the meso-scale numerical model can effectively simulate the mechanical behavior of RC short columns under axial load. Moreover, with the increase of fired surfaces and fire duration, the peak bearing capacity, axial compression stiffness and ductility decrease. The mechanical properties of short columns decrease more quickly under non-uniform fire. By comparing the theoretical value with the numerical simulation value of Nut/Nu, it is found that the theoretical value is conservative.

Development of a Novel Carbon-Fiber Mono-Lateral External Fixator

This paper reports the design of an innovative mono-lateral external fixator made of carbon fiber composite materials. The designed system can be easily assembled in comparison with commercial fixators and follows orthopedic requirements with sufficient stability and stiffness. The change of operation mode between distraction and fixation is achieved with a wedge that blocks axial translation in one position, while allows sliding with a 90º rotation. The prototypes were produced by the method of molding by compaction. A mold was developed for each part; the rail, the clamp and the cover. Each mold consisted of a cavity that gave form to the piece and a piston that exerted pressure on the composite. Mechanical tests were performed to determine the stiffness under axial compression, and anteroposterior and mediolateral bending. For comparison, tests were also performed on two Orthofix commercial systems, one with the rail made of carbon fiber and the other with an aluminum rail. The axial compression, anteroposterior and mediolateral bending stiffness of the developed system were 200.7, 13.4 and 87.0 N/mm, respectively, which were 38%, 35% and 27% lower than those obtained for the Orthofix system. However, these values were in the range of other similar systems reported in the literature. Therefore, the developed system presented promising results and may be clinically evaluated.

A biomechanical matched-pair comparison of two different locking plates for tibial diaphyseal comminuted fracture: carbon fiber-reinforced poly-ether-ether-ketone (CF-PEEK) versus titanium plates

BackgroundSeveral methods have been proposed to reduce plate construct stiffness and promote secondary bone healing. In this study, we explored the stiffness and strength of the new carbon fiber-reinforced poly-ether-ether-ketone (CF 50) plate compared with the titanium alloy plate (Ti6Al4V).MethodsTitanium and CF-PEEK locking plates were tested in a tibial non-osteoporotic diaphyseal comminuted fracture model to determine construct stiffness in axial compression, torsion, and bending. Subsequently, constructs were loaded until construct failure to determine construct strength.ResultsRelative to the titanium locking plate, the stiffness of the CF-PEEK locking plate was 6.8% and 30.8% lower in 200 N and 700 N axial compression, respectively (P < 0.05), 64.9% lower in torsion (P < 0.05), and 48.9% lower in bending (P < 0.05). The strength of the CF-PEEK locking plate was only 2.6% lower under axial compression, 7.8% lower in torsion, and 4.8% lower in bending than the titanium locking plate (P > 0.05).ConclusionsThe CF-PEEK locking plate significantly reduced axial, torsion, and bending stiffness compared with the titanium locking plate. Nonetheless, axial, torsional, and bending strength showed only a modest reduction. Considering its other advantages, which include radiolucency and artifact-free imaging, the CF-PEEK locking plate therefore deserves further clinical investigation.

Fabrication and analysis of mechanical properties of PVC/Glass fiber/graphene nano composite pipes

The aim of this work is to examine the conventional moulding method for manufacturing the PVC/Glass fiber/graphene nano composites. Uniform graphene dispersion is observed with the matrix for better bonding. The Mechanical properties of the manufactured nano composites have been done in this work. Three important standard tests were evaluated for the performance of Nano-Composites developed. The composites were developed as flat specimen for pipe applications. The three standards test which includes axial tension, compression and transverse compression is studied. The graphene nano composites were varied 0.5%, 1%, 1.5% and 2 percentages. Based on the results it can be concluded that the increase in the percentages of graphene made a uniform dispersion, which leads to increase in the compressive strength of the Nanocomposite. Increase in the axial compressive strength and stiffness was observed and the increase in the trend value is mainly observed in 1.5 wt% and 2 wt% respectively. The Graphene dispersion and fractured surface morphology of nano composites were examined using scanning electronic microscopy (SEM).It can also be used as an alternative for metal pipes in industries.

Optimal configuration of a dual locking plate for femoral allograft or recycled autograft bone fixation: A finite element and biomechanical analysis

BackgroundAllografts and recycled bone autograft are commonly used for biological reconstruction. The dual locking plates fixation method has been advocated for increasing allograft stability and preventing fixation failure; however, the biomechanical properties of the various configurations of dual locking plates have not been extensively studied. MethodsIn a finite element (FE) analysis, we developed 6 patterns of different dual locking plate configurations for fixation of the mid shaft of the femur. The maximum strains were recorded for each of the 6 models then axial, bending and torsion stiffness were calculated. The FE analysis was validated the results with mechanical testing (axial compression, bending, and torsional stiffness) on a cadaveric femur. FindingsThe highest axial compression (715.41 N/mm) and lateral bending (2981.24 N/mm) was found in Model 4 (with two 10-hole locking plates placed at the medial and lateral side), while the highest torsional stiffness (193.59 N·mm /mm) was found in Model 3 (with 8- and 10-hole locking plates placed at the posterior and lateral side). Excellent agreement was found between the finite element analysis and biomechanical testing (r2 = 0.98). InterpretationThe dual locking plate configuration with medial and lateral, 10-hole locking plates provided the most rigid and strongest fixation of the femur; both in terms of axial compression and lateral bending stiffness.

Experimental investigation of fire-exposed steel tubular stub columns wrapped with CFRP sheets

This paper investigates the effect of high temperature (600 °C, 800 °C, 1000 °C and 1100 °C) and the layers of carbon fibre reinforced plastics (CFRP) sheets (one, two, three, four) on the behaviour of fire-exposed steel tubular stub columns. Forty specimens were tested to investigate the failure modes, ultimate bearing capacity under axial compression, load-strain relationship, load-displacement relationship and initial stiffness of the specimens. Ultimate bearing capacity and initial stiffness decrease with the increase of temperature. The ultimate bearing capacity and ductility of fire-exposed specimens wrapped with CFRP sheets increase with the increase of CFRP sheets layers. After being strengthened by CFRP sheets with the same number of winding layers, circular steel tubular (CST) stub columns obtained a greater load-bearing capacity increase than square steel tubular (SST) stub columns. The largest enhancement of the ultimate bearing capacity of fire-exposed specimens is 59.47%. A recommended formula for the calculation of ultimate bearing capacity of fire-exposed specimens wrapped with CFRP sheets is proposed.

Experimental study of the behavior of prefabricated lightweight concrete shear walls with channel sections framing under axial compression

In order to satisfy requirements of fireproof and thermal insulation property of lightweight steel and lightweight concrete structures, an innovative prefabricated lightweight concrete shear wall with channel sections framing is developed. This paper focuses on axial compressive behavior of the wall. Two full-scale specimens are tested under axial compressive loads. The compressive strength of ceramsite-foamed concrete is varied to investigate their impacts on axial bearing capacity and axial compressive stiffness of the specimens. The failure modes, load-displacement curves, and deformability of the specimens are also investigated. Test results show that the failure modes of shear wall are mainly local bucking failure of channel sections framing and local crushing of ceramsite-foamed concrete plate. Compared with the specimen infilled C7-grade ceramsite-foamed concrete, the axial bearing capacity and the axial compressive stiffness of infilled C10-grade ceramsite-foamed concrete specimen are increased by 15.6% and 16.3%, respectively. Therefore, this study can provide a reference for further research on the axial compression performance of the prefabricated lightweight concrete shear walls with channel sections framing.

Axial compression performance of thin-walled T-shaped concrete filled steel tubular columns under constant high temperature: Experimental and numerical study

This study investigates the effects of temperature and stiffener on the axial compression performance of thin-walled T-shaped concrete filled steel tubular (CFST) stub columns. Eight CFST columns with and without stiffener were fabricated and exposed to different elevated temperatures, then tested for axial compressive performance. The complete load-displacement curve of the specimens under axial compression, the failure pattern after test and the failure characteristics of concrete core are also discussed. The finite element analysis is then developed to establish the calculation model of temperature field and axial pressure field of thin-walled T-shaped concrete filled steel tubular stub columns with stiffeners at constant high temperature. The FE model presents a highly agreement with experimental data in term of load-displacement behavior, which enable to further investigate stress distribution and failure mechanism of the columns. In addition, parametric study is conducted showing that temperature, thickness of steel tube, yield strength of steel tube and compressive strength of concrete are the key factors in contributing to axial compressive performance of the CFST stub columns. Finally, to provide reference for practical application of engineering, a simplified calculation formula for ultimate bearing capacity and axial compression stiffness of CFST stub columns were obtained via the regression analysis based on results from the experimental and numerical analysis. The result shows that the relative errors between results calculated from simplified formulae and from FE models are within 10%, which indicates that the proposed formulae are able to provide the theoretical reference for the practical engineering applications.

Investigating the biomechanical function of the plate-type external fixator in the treatment of tibial fractures: a biomechanical study

BackgroundThe design of an external fixator with the optimal biomechanical function and the lowest profile has been highly pursued, as fracture healing is dependent on the stability and durability of fixation, and a low profile is more desired by patients. The plate-type external fixator, a novel prototype of an external tibial fixation device, is a low profile construct. However, its biomechanical properties remain unclear. The objective of this study was to investigate the stiffness and strength of the plate-type external fixator and the unilateral external fixator. We hypothesized that the plate-type external fixator could provide higher stiffness while retaining sufficient strength.MethodsFifty-four cadaver tibias underwent a standardized midshaft osteotomy to create a fracture gap model to simulate a comminuted diaphyseal fracture. All specimens were randomly divided into three groups of eighteen specimens each and stabilized with either a unilateral external fixator or two configurations of the plate-type external fixator. Six specimens of each configuration were tested to determine fixation stiffness in axial compression, four-point bending, and torsion, respectively. Afterwards, dynamic loading until failure was performed in each loading mode to determine the construct strength and failure mode.ResultsThe plate-type external fixator provided higher stiffness and strength than the traditional unilateral external fixator. The highest biomechanics were observed for the classical plate-type external fixator, closely followed by the extended plate-type external fixator.ConclusionsThe plate-type external fixator is stiffer and stronger than the traditional unilateral external fixator under axial compression, four-point bending and torsion loading conditions.

Load-transfer in the human vertebral body following lumbar total disc arthroplasty: Effects of implant size and stiffness in axial compression and forward flexion.

Adverse clinical outcomes for total disc arthroplasty (TDA), including subsidence, heterotopic ossification, and adjacent‐level vertebral fracture, suggest problems with the underlying biomechanics. To gain insight, we investigated the role of size and stiffness of TDA implants on load‐transfer within a vertebral body. Uniquely, we accounted for the realistic multi‐scale geometric features of the trabecular micro‐architecture and cortical shell. Using voxel‐based finite element analysis derived from a micro‐computed tomography scan of one human L1 vertebral body (74‐μm‐sized elements), a series of generic elliptically shaped implants were analyzed. We parametrically modeled three implant sizes (small, medium [a typical clinical size], and large) and three implant materials (metallic, E = 100 GPa; polymeric, E = 1 GPa; and tissue‐engineered, E = 0.01 GPa). Analyses were run for two load cases: 800 N in uniform compression and flexion‐induced anterior impingement. Results were compared to those of an intact model without an implant and loaded instead via a disc‐like material. We found that TDA implantation increased stress in the bone tissue by over 50% in large portions of the vertebra. These changes depended more on implant size than material, and there was an interaction between implant size and loading condition. For the small implant, flexion increased the 98th‐percentile of stress by 32 ± 24% relative to compression, but the overall stress distribution and trabecular‐cortical load‐sharing were relatively insensitive to loading mode. In contrast, for the medium and large implants, flexion increased the 98th‐percentile of stress by 42 ± 9% and 87 ± 29%, respectively, and substantially re‐distributed stress within the vertebra; in particular overloading the anterior trabecular centrum and cortex. We conclude that TDA implants can substantially alter stress deep within the lumbar vertebra, depending primarily on implant size. For implants of typical clinical size, bending‐induced impingement can substantially increase stress in local regions and may therefore be one factor driving subsidence in vivo.

Simulation analysis and experiment research of stiffness variable shock isolator for large-scale marine equipment

In order to analyze working performance of shock isolators for large-scale marine equipment under heavy shock load, a certain type of stiffness variable shock isolator was studied by conducting FEA calculation and shock experiments. Good agreement between the simulation and experiments proves the efficiency of calculation method. Results show that the shock isolator can provide alterable stiffness in axial compression, and absorb enough shock energy within restricted area to achieve shock isolation and elastic limit of equipment in harmony.

Lateral-torsional buckling of box beam with corrugated steel webs

Corrugated steel web is folded along the longitudinal direction and has the mechanical properties such as axial compression stiffness corrugation effect, shear modulus corrugation effect, similar to that of an accordion. In order to study the lateral-torsional buckling of box beams with corrugated steel webs (BBCSW) under the action of bending moment load, the neutral equilibrium equation of BBCSW under the action of bending moment load is derived through the stationary value theory of total potential energy and further, along with taking Kollbrunner-Hajdin correction method and the mechanical properties of the corrugated web into consideration. The analytical calculation formula of lateral-torsional buckling critical bending moment of BBCSW is then obtained. The lateral-torsional buckling critical bending moment of 96 BBCSW test specimens with different geometry dimensions are then calculated using both the analytical calculation method and ANSYS finite element method. The results show that the analytical calculation results agree well with the numerical calculation results using ANSYS, thus proving the accuracy of the analytical calculation method and model simplification hypothesis proposed in this paper. Also, compared with the box beams with flat steel webs (BBFSW) with the same geometry dimensions as BBCSW, within the common range of web space-depth ratio and web span-depth ratio, BBCSW’s lateral-torsional buckling critical bending moment is larger than that of BBFSW. Moreover, the advantages of BBCSW’s stability are even more significant with the increase of web space-depth ratio and web depth-thickness ratio.

Experimental Investigation on Stability of Circular Steel Tubular Stub Columns at Elevated Temperatures Under Axial Compression

This paper studies the structural stability of circular steel tubular stub columns at elevated temperatures under axial compression. Fifty-one specimens are subjected to high-temperature treatment and axial compression. The variables of the specimen are temperature, wall thickness of steel tube and duration of high temperature. The displacement–load curve, strain–load curve, ultimate load, axial compressive stiffness and failure characteristics of the specimens were analyzed. Test results show that after exposure to high temperatures, the specimens’ failure phenomenon in the axial compression loading test is consistent with that at room temperature, the bearing capacity decreases considerably, the ductility decreases slightly and the axial compressive stiffness changes irregularly. Temperature is the determining factor of the ultimate load of the specimen, and the reducing extent of ultimate load increases with the temperature. When the temperature reaches 1000∘C, its maximum reducing extent exceeds 50%. Among the three parameters considered in this study, the duration of high temperature has the least influence on the specimen.

Experimental evaluation of built-in channel steel concrete-filled GFRP tubular stub columns under axial compression

This paper studies experimentally the structural behavior of channel steel reinforced concrete-filled glass fiber-reinforced polymer (GFRP) tubular stub columns. To understand their structural performance, we examined 27 specimens which subjected to axial compression. The variables of the specimen are concrete strength grade, diameter-to-thickness ratio of GFRP tube and steel ratio. The displacement-load curve, strain-load curve, ultimate load, axial compressive stiffness and failure characteristics of the specimens were analyzed. The results of the test show that the specimens’ ultimate bearing capacity increases as the concrete strength increases. And those specimens with higher concrete strength grade have greater initial stiffness and better deformation capacity than those with lower concrete strength grade. The varieties of the steel ratio have no significant effect on the specimens’ axial deformation property. The confinement coefficient is proposed to evaluate the constraint effect of the GFRP tube on both the inner channel steel and the core concrete. There was a negative correlation between the restraint effect and the diameter-thickness ratio of the GFRP tube. A simplified formula for calculating the axial bearing capacity of the composite columns is proposed.

Biomechanical Effects of an Oblique Lumbar PEEK Cage and Posterior Augmentation

Lumbar interbody spacers are widely used in lumbar spinal fusion. The goal of this study is to analyze the biomechanics of a lumbar interbody spacer (Clydesdale Spinal System, Medtronic Sofamor Danek, Memphis, Tennessee, USA) inserted via oblique lumbar interbody fusion (OLIF) or direct lateral interbody fusion (DLIF) approaches, with and without posterior cortical screw and rod (CSR) or pedicle screw and rod (PSR) instrumentation. Lumbar human cadaveric specimens (L2-L5) underwent nondestructive flexibility testing in intact and instrumented conditions at L3-L4, including OLIF or DLIF, with and without CSR or PSR. OLIF alone significantly reduced range of motion (ROM) in flexion-extension (P= 0.005) but not during lateral bending or axial rotation (P ≥ 0.63). OLIF alone reduced laxity in the lax zone (LZ) during flexion-extension (P < 0.001) but did not affect the LZ during lateral bending or axial rotation (P ≥ 0.14). The stiff zone (SZ) was unaffected in all directions (P ≥ 0.88). OLIF plus posterior instrumentation (cortical, pedicle, or hybrid) reduced the mean ROM in all directions of loading but only significantly so with PSR during lateral bending (P=0.004), without affecting the compressive stiffness (P> 0.20). The compressive stiffness with the OLIF device without any posterior instrumentation did not differ from that of the intact condition (P= 0.97). In terms of ROM, LZ, or SZ, there were no differences between OLIF and DLIF as standalone devices or OLIF and DLIF with posterior instrumentation (CSR or PSR) (P > 0.5). OLIF alone significantly reduced mobility during flexion-extension while maintaining axial compressive stiffness compared with the intact condition. Adding posterior instrumentation to the interbody spacer increased the construct stability significantly, regardless of cage insertion trajectory or screw type.

Four cannulated screws in self-designed configurations for fixation of extremely unstable femoral neck fractures: a biomechanical analysis

Objective To investigate the biomechanical properties of our self-designed 4 cannulated screws in 4 configurations for fixation of extremely unstable femoral neck fractures. Methods Twelve adult cadaveric femoral specimens were randomly divided into 4 equal groups (n=3) and made into models of extremely unstable femoral neck fracture combined with comminution (Pauwels type Ⅲ). Group A was subjected to fixation in configuration of axial compressions plus double stabilizations , group B to configuration of positive triangle parallel compression plus small angle screwing , group C to configuration of inverted triangle parallel compression plus small angle screwing , and group D to configuration of diamond pattern screwing . Static compression tests, cyclic loading tests and limit load tests were carried out for the 4 groups on a biomechanical testing machine. Results For groups A, B C and D, the axial compression stiffness was respectively 995.29±34.16 N/mm, 509.89±138.90 N/mm, 559.28±111.25 N/mm and 610.18±232.35 N/mm, and the limit load was respectively 3, 225.33±461.31 N, 2, 008.67±237.27 N, 2, 705.67±496.39 N and 2, 395.33±403.71 N, showing significant differences between the 4 groups (P 0.05). Conclusions In the fixation of extremely unstable femoral neck fracture with our self-designed 4 cannulated screws, the configuration of axial compressions plus double stabilizations may lead to the greatest biomechanical advantage while the configuration of positive triangle parallel compression plus small angle screwing may result in the poorest biomechanical properties. Key words: Femoral neck fractures; Fracture fixation, internal; Bone nails; Biomechanics