Longitudinal Compression Test Research Articles

The Longitudinal Compression Capacity of Hollow Concrete Cylinders Prestressed by Means of an SMA Wire.

This paper deals with the mechanical behavior of hollow concrete cylinders prestressed with nickel-titanium (Ni-Ti)-shape memory alloy (SMA) wires wound around them. Prestresses can be created by the thermal activation of the memory effect of SMA wire placed on the outer surface of concrete cylinders. In order to assess the stress level in concrete, a model was used to analyze the thermal stresses in the concrete shell resulting from a temperature gradient in the thickness. Another model was used to calculate the circular concentric loading applied by the wound wire resulting from the impairment of its memory effect by the concrete cylinder. Finally, longitudinal compression tests were performed on the prestressed hollow cylinders. Longitudinal and circumferential strains were measured using gauges located on the surfaces of the hollow cylinders. The tests were performed almost one year after the application of prestressing by means of Ni-Ti SMA wire, confirming that the residual stress in the wire remained present. It may therefore be concluded that the prestressing of concrete elements designed with the use of Ni-Ti SMA material is effective for a long time.

Correlation Analysis of Ultrasonic Stress Wave Characteristics and the Destructive Strength Measurements in Cylindrical Wooden Structure.

The utility sector has been employing ultrasonic-based nondestructive evaluation (NDE) to determine the cross-sectional groundline integrity of wooden utility poles. While it is far less invasive than other methods, its efficacy has not been thoroughly studied. This study aims to fill this technical gap by analyzing the correlation between the propagational characteristics of the ultrasonic stress wave using a novel embedded waveguide technique and the existing destructive testing methods. The proposed embedded waveguide technique excites diffusive Rayleigh mode (AW2) propagating in the shell region of the cross-sectional plane. This discovery allows a direct examination of the shell region condition through stress wave analysis. By employing the Gabor wavelet transformation and the model-based arrival region identification, this proposed technique extracts the propagation velocity and the associated spectral response of AW2. This study uses the static break assessment per ASTM 1036 Standard Test Methods And The longitudinal compression test per ASTM D143-14 "secondary method" to quantify the cross-sectional strength of the test specimen. This work performs a comprehensive correlation analysis between the extracted AW2 features and the associated destructive test. An overall correlation R2 from 0.2 to 0.5 is achieved between the AW2 features and the static break test results. An overall correlation of R2 of 0.4 is achieved for 30-35 ft poles in the longitudinal compression test.

Longitudinal compression failure of 3D printed continuous carbon fiber reinforced composites: An experimental and computational study

Fused filament fabrication (FFF) with continuous carbon fiber filaments has proven to be a promising manufacturing technique in engineering applications. To provide guidance in the design of 3D printed carbon fiber reinforced polymer (CFPR) components, the longitudinal compression failure of continuous CFPR composites using the FFF technique is investigated systematically. First, longitudinal compression tests are performed for 3D printed continuous CFRP composites with and without designed waved filaments. The degradation of the failure strength is remarkable when the waved filaments are introduced. Nevertheless, further degradation is limited when more waved filaments are adopted. Next, the fracture morphologies are analyzed, and in-plane and out-of-plane kink-bands are observed in the microscopic images. For the specimens with waved filaments, fracture occurs at the cross-section with the contact region of the waved and regular filaments, as well as the cross-section with the maximum misalignment angle. Correspondingly, a computational framework for 3D printed continuous CFPR composites is established to explore the longitudinal compression failure mechanisms. The meso-scale computational models are reconstructed according to the geometric features of the deposited continuous CFRP filaments and the actual void volume fraction. The elastic properties of the filament are calculated by a micro-scale representative volume element (RVE) model, which is based on the fiber random distribution algorithm. The plastic deformation and failure is described by a filament constitutive model which is established by the Liu-Huang-Stout yield criterion and a simplified Tsai-Wu failure criterion. The experimental validation demonstrates the feasibility of the computational models to predict the stress-strain curves of 3D printed materials, and also capture the realistic longitudinal compression failure behavior.

Fabrication and characterization of customized tubular scaffolds for tracheal tissue engineering by using solvent based 3D printing on predefined template

Purpose This paper aims to discuss the successful fabrication of customized tubular scaffolds for tracheal tissue engineering with a novel route using solvent-based extrusion 3D printing. Design/methodology/approach The manufacturing approach involved extrusion of polymeric ink over a rotating predefined pattern to construct customized tubular structure of polycaprolactone (PCL) and polyurethane (PU). Dimensional deviation in thickness of scaffolds were calculated for various layer thicknesses of 3D printing. Physical and chemical properties of scaffolds were investigated by scanning electron microscope (SEM), contact angle measurement, Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). Mechanical characterizations were performed, and the results were compared to the reported properties of human native trachea from previous reports. Additionally, in vitro cytotoxicity of the fabricated scaffolds was studied in terms of cell proliferation, cell adhesion and hemagglutination assay. Findings The developed fabrication route was flexible and accurate by printing customized tubular scaffolds of various scales. Physiochemical results showed good miscibility of PCL/PU blend, and decrease in crystalline nature of blend with the addition of PU. Preliminary mechanical assessments illustrated comparable mechanical properties with the native human trachea. Longitudinal compression test reported outstanding strength and flexibility to maintain an unobstructed lumen, necessary for the patency. Furthermore, the scaffolds were found to be biocompatible to promote cell adhesion and proliferation from the in vitro cytotoxicity results. Practical implications The attempt can potentially meet the demand for flexible tubular scaffolds that ease the concerns such as availability of suitable organ donors. Originality/value 3D printing over accurate predefined templates to fabricate customized grafts gives novelty to the present method. Various customized scaffolds were compared with conventional cylindrical scaffold in terms of flexibility.

Strain-rate and off-axis loading effects on the fibre compression strength of CFRP laminates: Experiments and constitutive modelling

A series of dynamic longitudinal compression tests have been performed on cross-ply IM7/8552 specimens cut at different off-axis angles to produce different combinations of compression and shear stresses. Together with results from previous quasi-static tests of the same kind, quasi-static and dynamic fibre kinking failure envelopes have been obtained using classical laminate theory. This new experimental data has been compared against predictions from the leading fibre kinking theories, made rate-dependent by using rate-dependent in-plane shear properties, and show that, while they can accurately predict the effects of strain rate on the uniaxial compression strength, they are unable to capture the effects of shear, neither at quasi-static nor dynamic rates. Instead, a simpler more phenomenological approach is proposed to predict the rate-dependent fibre kinking strength of FRP laminates under multi-axial loads until the micromechanics can be more accurately described.

选区激光熔化成型316L不锈钢多孔结构的力学性能

In order to reduce or eliminate the stress shielding effect of artificial implants and improve the biocompatibility, mechanical properties of porous structures formed by selective laser melting (SLM) technology need to be studied. Through the preparation of 316L stainless steel body core cubic (BCC) and regular dodecahedron (RD) porous structures, the longitudinal compression test of the molded parts was carried out respectively, and the Gibson-Ashby model was established to predict the elastic modulus value of the porous structure. The effects of porosity, average pore diameter and specific surface area on elastic modulus and compressive strength of porous structures were analyzed by fractal interpolation. The analysis results show that when the porosity of 316L stainless steel porous structure sample is 55.13%-94.74%, the average pore diameter is 1.90-4.22 mm, and the specific surface area is 0.54-4.33, the elastic modulus is 0.375-1.716 GPa, and the compressive strength is 43.19-160.31 MPa. The elastic modulus of human bone was 0.9-1.7 GPa, which meets the requirements of implants. Porosity, average pore diameter and specific surface area have little influence on the elastic modulus and the amplitude of compressive strength of the dodecahedral porous structure, but have greater influence on the body-centered cubic porous structure. The compressive strength of the dodecahedron porous structure is 111.75-160.31 MPa, and the compressive strength of the body centered cubic porous structure is 43.19-158.03 MPa. The performance of the dodecahedron porous structure is better than that of the body centered cubic structure. This paper provides the basis for the research on the preparation of 316L stainless steel porous structure by selective laser melting.

Compression test of a single carbon fiber in a scanning electron microscope and its evaluation via finite element analysis

A longitudinal compression test for a single polyacrylonitrile-based carbon fiber (T300) was performed using a scanning electron microscope. The compressive stress/strain behavior was initially linear, but subsequently became nonlinear. The longitudinal tangent modulus decreased with increasing compressive strain. A cyclic compression test revealed that the T300 carbon fiber deformed elastically up to ~90% compressive strength. The variability in the compressive strength was evaluated using Weibull analysis. The representative compressive strength of the T300 carbon fiber was nearly the same as the tensile strength. The compressive strength of the T300 carbon fiber was almost same as that of the high-tensile strength T800S carbon fiber. Finite element analysis was performed to investigate the validity of the test method. The results showed that the longitudinal compressive stress on the carbon fiber varied during longitudinal compressive loading. The maximum longitudinal compressive stress in the carbon fiber was slightly higher than the average compressive strength applied at the end. However, the variability in the measured compressive strength was much higher than that in the longitudinal compressive stress on the carbon fiber, which does not affect the former.

Micro-finite-element method to assess elastic properties of trabecular bone at micro- and macroscopic level

The objective of the present study is to assess the mechanical behavior of trabecular bone based on microCT imaging and micro-finite-element analysis. In this way two methods are detailed: (i) direct determination of macroscopic elastic property of trabecular bone; (ii) inverse approach to assess mechanical properties of trabecular bone tissue. Thirty-five females and seven males (forty-two subjects) mean aged (±SD) 80±11.7 years from hospitals of Assistance publique-Hôpitaux de Paris (AP-HP) diagnosed with osteoporosis following a femoral neck fracture due to a fall from standing were included in this study. Fractured heads were collected during hip replacement surgery. Standardized bone cores were removed from the femoral head's equator by a trephine in a water bath. MicroCT images acquisition and analysis were performed with CTan® software and bone volume fraction was then determined. Micro-finite-element simulations were per-formed using Abaqus 6.9-2® software in order to determine the macroscopic mechanical behaviour of the trabecular bone. After microCT acquisition, a longitudinal compression test was performed and the experimental macroscopic Young's Modulus was extracted. An inverse approach based on the whole trabecular bone's mechanical response and micro-finite-element analysis was performed to determine microscopic mechanical properties of trabecular bone. In the present study, elasticity of the tissue was shown to be similar to that of healthy tissue but with a lower yield stress. Classical histomorphometric analysis form microCT imaging associated with an inverse micro-finite-element method allowed to assess microscopic mechanical trabecular bone parameters.

Carbon/epoxy filament wound composite drive shafts under torsion and compression

Composite cylinders to be used as half shafts must satisfy several requirements, such as critical speed, critical buckling torque, and load carrying ability. This study focused on the investigation of carbon fiber reinforced epoxy composite cylinders produced by filament winding to be used as half shafts. A preliminary torsional test in a [±45]5 cylinder was performed and three other laminates were chosen for the study: [±22/±45], [±89/±45], and [±45/±45]. Radial and longitudinal compression tests were performed. Mechanical analysis has been carried out using analytical and numerical approaches, and good correlation was found between them and the experimental values. The [±45/±45] cylinder showed the best performance under torsional loading, as expected, as well as radial and longitudinal compression, but not critical buckling torque.

Influence of a wide range of moisture contents on the Poisson’s ratio of wood

This study investigates the effect of a wide range of moisture contents (0–177 %) on the Poisson’s ratio of wood taken from Japanese cypress and magnolia by conducting longitudinal compression tests. Through analysis of variance and multiple comparisons, it was found that when the moisture content is below the respective fiber saturation point Poisson’s ratio decreases with increasing moisture content. In contrast, at moisture contents above the fiber saturation point, the Poisson’s ratio increases with moisture content. The same tendency was observed in both wood species, but the effect was more pronounced in magnolia than Japanese cypress.

Influence of sterilization treatments on continuous carbon-fiber reinforced polyolefin composite

To evaluate the influence of sterilization treatment on continuous carbon-fiber reinforced polyolefin composite (CFRP) so as to provide experimental reference for selection of sterilization method for CFRP. Seventy bars of CFRP were divided into 7 equal groups to undergo sterilization by autoclave, 2% glutaraldehyde soaking, 75% alcohol soaking, ethylene oxide sterilization, and Co-60 gamma ray irradiation of the dosages 11 kGy, 25 kGy, and 18 kGy respectively, and another 10 bars were used as blank controls. Then the bars underwent three-point bending test and longitudinal compression test so as to measure the biomechanical changes after sterilization treatment, including the maximum load, ultimate strength, and elastic modulus. Three-point bending test showed that the levels of maximum load of the all experimental groups were lower than that of the control group, however, only those of the 3 Co-60 irradiation groups were significantly lower than that of the control group and that Co-60 radiation lowered the level of maximum load dose-dependently; and that the levels of ultimate strength of all the all experimental groups were lower than that of the control group, however, only those of the 3 Co-60 groups were significantly lower than that of the control group and that the higher the dosage of Co-60 radiation the lower the level of ultimate strength, however, not dose-dependently. The elastic modulus of the Co-60 25 KGy group was significantly higher than that of the control group, and there was no significant difference in the level of ultimate strength among the other groups. Longitudinal compression test showed that the levels of maximum load and ultimate strength of the 3 Co-60 irradiation groups, autoclave group, and circular ethylene groups were significantly lower than that of the control group, and there was no significant difference in elastic modulus among different groups. During sterilized package of CFRP products produced in quantity autoclave sterilization and Co-60 gamma ray irradiation sterilization should be avoided. Ethylene oxide is proposed as the best sterilization method. If gamma ray irradiation is to be used further technology improvement is necessary.

High-frequency oscillatory motions enhance the simulated mechanical properties of non-weight bearing trabecular bone

Extremely low-level oscillatory accelerations, applied without constraint, can increase bone formation. Here, we tested the hypothesis that high-frequency oscillations, applied in the absence of functional weight bearing, can be sensed by trabecular bone to produce a structure that is more efficient in sustaining applied loads. The left leg of anesthetized adult female mice ( n=18) was subjected to high-frequency oscillations at 45 Hz, 0.6 g for 20 min/day, 5 days/week for 3 weeks, while the contralateral leg served as an internal control. To remove the potential interference of the habitual strain environment with the imposed physical signal, the hindlimbs of these mice were chronically unloaded. In vivo microCT scans of the proximal metaphyseal region of the tibia were transformed into finite element meshes to evaluate trabecular and cortical mechanical properties. Simulated longitudinal compression tests showed that the short applications of high-frequency oscillations were sensed primarily by trabecular bone. At the end of the experimental period, apparent trabecular stiffness of the oscillated bones was 38% ( p<0.001) greater than that of non-weight bearing controls. Simulated uniaxial loads applied to trabecular bone induced 21%, 52%, and 131% greater ( p<0.05) median, peak compressive, and peak tensile longitudinal stresses in control than in stimulated bones. Non-weight bearing control bones were also characterized by greater transverse normal and shear stresses (77% and 54%, respectively, p<0.001) as well as 35% greater ( p=0.03) longitudinal shear stresses. Compared to normal age-matched controls ( n=18), oscillations were able to attenuate, but not fully prevent, the decline in trabecular mechanical properties associated with the removal of weight bearing. These data indicate not only that bone cells can sense low-level, high-frequency oscillatory accelerations, but also that they can orchestrate a structural response that produces a stiffer trabecular structure that may be less prone to fracture.

INVESTIGATIONS ON THE FIBRE FRACTURE BEHAVIOUR OF CFRP LAMINATES UNDER BIAXIAL LOADING

The present tailure criteria for the prediction of fibre fracture in composite laminates are simple maximum stress or maximum strain criteria. They do not consider any possible interaction of transverse stresses or strains. There are theoretical considerations by Hart-Smith and some rare experimental results that there might be a considerable impact of transverse strains on the longitudinal ultimate strain of CFRP. This is an important but presently unanswered question for the safe design of composite laminates. In this work, filament wound tubular specimens are tested under torsion to induce a biaxial stress state in a unidirectional CFRP ply. The specimens are accurately designed With consideration of nonlinear material behaviour by means of analytical methods for thick-walled tubes. The specimen laminate consists of a 45° CFRP test layer and several ±45° GFRP support layers. A series of longitudinal tensile tests and longitudinal compression tests for one particular strain ratio is carried out. The experiments indicate that there seems to be an impact of transverse strains on the longitudinal strength, but the strength is not cut to half as postulated by Hart-Smith.

Compressive properties of single-filament carbon fibres

Compressive properties of mesophase pitch-based carbon fibres (NT-20, NT-40 and NT-60) were measured using the tensile recoil test and the elastica loop test. The NT-40 fibre with a 400 GPa tensile modulus showed a smaller loop compressive yield strain and a larger recoil compressive strength compared to these values obtained from the longitudinal compression test on its unidirectional composites. Further, the recoil compressive strength of this fibre was higher than that of PAN-based carbon fibre with a corresponding modulus. Under the ideal conditions in the tensile recoil test, the strain energy was conserved before and after recoil, and the initial tensile stress and the recoil compressive stress do not coincide when fibre stress-strain behaviour is non-linear, and the non-linearity in compression and in tension is different. The difference between the composite compressive strength and the recoil compressive strength of NT-40 was quantitatively explained by taking account of the fibre compressive stress-strain non-linear relation. The difference between the loop compressive yield strain and the composite compressive strain to failure was also explained by this non-linearity.

Estimation of Mechanical Properties of the Distal Radius from Bone Mineral Content and Cortical Width

Bone mineral content (BMC) was determined by photon absorptiometry and cortical width (CW) by radiographic morphometry at two levels in 17 radii obtained postmortem from women ranging in age from 39 to 95 years. One level was the region in which Colles' fracture occurs (lower level) and the other about 6 cm from the styloid tip (upper level). Principal compressive strain at a 600-N load, fracture load, compliance, and work/unit length to fracture were measured in longitudinal compression tests. In general, BMC provides more precise estimates of mechanical properties than CW. The correlation coefficient between fracture load and BMC at the lower level was +0.83 (less than 0.001). Between work/unit length to fracture and BMC the coefficient was +0.81 (p less than 0.001).

A correlation between acoustic emission and the fracture toughness of 2124-T851 aluminum

The paper reports on an experimental study of the possible application of acoustic emission as an inspection technique, to determine whether 2124-T851 aluminum plate meets certain, minimum, fracture toughness specifications. Unflawed specimens, taken in the three principal directions, from three separate plates are tested in compression and tension. The-true-mean-square or the root-mean-square voltage of the continuous acoustic emission generated during the tests is recorded as a function of specimen strain. The acoustic emission, chemical analysis, fracture surfaces, and large (1–20 μm) second-phase particles are studied in relation to fracture toughness. Results indicate that the generated acoustic emission from a longitudinal compression test, long-transverse tension test and short-transverse tension test all correlate with changes in plate fracture toughness. Based on the experimental results, the monitoring of acoustic emission during relatively simple tension or compression tests of aluminum may be useful in checking whether the material meets a fracture toughness specification. Also, the results indicate that acoustic emission is useful in studies to develop fructure toughness models.

Directional effects of prestrain in steel

Tension and compression tests were made on specimens cut from a steel plate which had been prestrained by 1·3 per cent, the specimens being at various angles to the prestraining axis. The Bauschinger effect was evident and a similar effect existed to a lesser degree for specimens with axes perpendicular to the straining direction. Longitudinal and transverse specimens were also tested from plates prestrained in tension by 3 and 5 per cent. The Bauschinger effect was well marked in the longitudinal compression tests but work hardening dominated in the transverse direction.