Specimen Axis Research Articles

Bending properties of particleboard and MDF layers

Abstract The modulus of elasticity in bending and the bending strength of the face and core layer of particleboard and medium density fiberboard (MDF) were determined. Three directions of longitudinal axis of test specimens were considered: the direction of the mat forming, the direction perpendicular to it, and the direction perpendicular to the panel plane. The experiments were carried out on specimens that were prepared with strips of layers separated from the panels and glued into laminated assemblies. The bending properties of the core and face layer of the tested panels differed considerably. The core layer properties were on average more than 4 times smaller for particleboard and almost 3 times smaller for MDF. The relative differences between the bending properties were greater than the differences between the densities of the layers. The bending properties of the layers were almost isotropic in the planes of layers and very strongly anisotropic in the planes perpendicular to layers. The modulus of elasticity of the tested panels was calculated for the axis corresponding to the mat forming direction. The calculations were performed on the basis of the moduli of panel layers and based on the layered system theory. The results were compared with the modulus determined directly for entire panels. The relative difference between the compared moduli was found to be very small for both tested panels.

Quenching cracks in medium carbon steel initiated at manganese sulfide inclusions

Abstract Quench crack propensity has been investigated for two identical medium carbon steels (50CrMo4) which only differed in sulfur content. The standard variant of the material was affected by manganese sulfide inclusions whereas the low sulfur material was essentially free of sulfides. 80 mm, cylindrical test specimens were used. The test specimens had been cut out of cross rolled steel plates in which the manganese sulfide were flattened to discoid shape. The specimen orientation was in direction of principal deformation where the flattened sulfides were aligned with the test specimen axis. The largest sulfides reached lengths of 150 mm. Both materials were austenitized at 850°C for 60 minutes, quenched in a salt-bath at 180°C and immediately annealed at 425°C for one hour. It turned out that the standard material developed quench cracks which initiated at manganese sulfide. No cracks could be found in the low sulfur material. Thermal and transformational stresses, which develop during quenching, a...

Research on three-dimensional shape reconstruction of circular cylindrical flaw

In this article, three-dimensional Born inverse scattering method is modified to convenient form for a cylindrical specimen that includes three-dimensional defect. One aluminum cylinder with flaw model is prepared and ultrasonic measurements are carried out. The measurement area in the modified methods is restricted in the plane perpendicular to the axis of cylindrical specimen. That’s to say that the method is modified to convenient form to use measured waveforms in the x 1 − x 2 plane. The measured wave data are fed into the inversion method and cross-sectional images are obtained. Then, three-dimensional shape reconstruction of flaw model in aluminum specimen is performed by piling up the cross-sectional images. At the same time, we get the numerical results from all directions by finite element method.

Shear-Type Fatigue Crack Growth in SAE52100 Steel

Shear-type fatigue crack behavior in a bearing steel, SAE52100, was investigated in a biaxial fatigue testing machine using cylindrical specimens. Either of the following two types of artificial defect with the total length of 400 ~ 440 %m and the depth of 200 ~ 300 %m was introduced into the specimen surfaces: (a) a semi-elliptical pre-crack emanating from 2 adjacent holes by a tension-compression loading, (b) 3 adjacent holes oriented in the axial direction which had slits made by the focused ion beam technique at the both ends. Fully reversed torsion with a shear stress amplitude at specimen surface, τa = ~ 600 MPa, was applied to the specimens under the static axial compressive stress σm = −1000 ~ −1200 MPa. In case of the defect (a), a shear-type crack propagated from the pre-crack in direction perpendicular to the specimen axis. At the specimen surface, the shear-type crack periodically branched from the crack tip and propagated 5~10 %m in Mode I directions. The shear-type crack growth was decelerated with an increase in the crack length and finally stopped at N ≅ 7.5×106 cycles and 2a ≅ 600 %m. On the other hand, in case of the defect (b), the shear-type crack propagated in axial direction, and the crack growth was accelerated with an increase in the crack length. In addition, the threshold stress in case without the compressive stress on crack-face was determined by a τa-decreasing test. The results revealed that the shear-type crack growth was strongly influenced by the crack-face friction and the existence of the Mode I blanched cracks.

Drying Shrinkage of Cement-Based Materials Under Conditions of Constant Temperature and Varying Humidity

Currently, deformations along the central axis of specimens were usually measured under fixed environmental conditions. Seldom were the effects of environmental factors on the drying-shrinkage deformation of cement-based material considered. For this paper, the drying-shrinkage deformation at different w/b ratios and different additions to mortars was investigated under different environments at a temperature of 20 °C and humidity ranging from 100% to 50%. The specimens were cured in water for 28 days before measurement. The results illustrate that mortar shows much less shrinkage under various drying conditions when a lower w/b ratio is adopted. With a decrease in relative humidity the speed of drying-shrinkage becomes gradually lower. The addition of silica fume reduces the drying-shrinkage of mortar under higher relative humidity, because the pore structure of mortar with silica fume becomes more refined. The addition of fly ash increases the total porosity and the volume of coarse pores in the mortar. The drying-shrinkage of mortar under different conditions increases with the addition of more of fly ash.

Dynamic Failure of Borosilicate Glass Under Compression/Shear Loading Experiments

Dynamic compression/shear experiments on a borosilicate glass at an average strain rate of 250 s−1are conducted using a modified version of a split Hopkinson pressure bar. Instead of applying confining pressure, cuboid specimens with the material axis inclining to the loading direction at different angles (0°, 3°, 5°, and 7°) are used to generate higher shear stresses. A high‐speed digital camera, synchronized with the loading stress pulse, is used to record the dynamic crack initiation and propagation. Experimental results show that the equivalent stress at failure decreases with increasing shear portion in the stress. Digital images show that the cracks initiate randomly in the right specimen, whereas cracks initiate from the stress‐concentrated corners in the inclined specimens. Subsequent crack propagation, despite specimen inclination angles, is along the specimen axis rather than the compressive loading direction.

Substrate stiffness determination in curved layered composites using bending methods

Bending tests are conveniently used to determine mechanically the elastic modulus of materials. However, in the case of asymmetrical, coated specimens that exhibit warping due to mismatch in thermal or isothermal expansion of the individual layers, non-linear deformation behaviour is present and the stiffness evaluation becomes difficult with this method. A bending test procedure is outlined which uses a flat composite specimen obtained by joining two spherically curved layered specimen along their coating surfaces. The elastic behaviour of the joint specimen essentially reflects the stiffness of the substrate since the thin coatings and the thin adhesive layer are located close to the neutral specimen axis of the bending test. The method is illustrated using warped anode-substrate/electrolyte sheets of solid oxide fuel cells. The results of ring-on-ring tests with anode substrate or electrolyte under tension and with the joint specimen are presented and discussed.

Evaluation of fatigue crack propagation by mode I and mixed mode in 1050 aluminium

The mechanism of mixed-mode fatigue crack propagation was investigated in pure aluminum. Push-pull fatigue tests were performed using two types of specimens. One was a round bar specimen having a blind hole, one was a plate specimen having a slit. The slit direction cut in the specimen was perpendicular or inclined 45 degrees relative to the centre of the specimen axis. In both cases, cracks propagated by mode I or by the mixed mode combining mode I and shear mode, depending on the testing conditions. In these cases the crack propagation rate was evaluated with a modified effective stress intensity factor range. Crack propagation retardation was observed in some specimens. However, it was found that the crack propagation rate could also be evaluated by the effective stress intensity factor range independent of the crack propagation mode.

Shape reconstruction of three-dimensional flaw from backscattering data

Three dimensional Born and Kirchhoff inverse scattering methods are modified to convenient forms for a cylindrical specimen that includes three dimensional defect. One aluminum cylinder with flaw model is prepared and ultrasonic measurements are carried out. The measurement area in the modified methods is restricted in the plane perpendicular to the axis of cylindrical specimen. That is to say that the methods are modified to convenient form to use measured waveforms in the x 1– x 2 plane. The measured wave data are fed into the inversion method and cross-sectional images are obtained. Then, three dimensional shape reconstruction of flaw model in aluminum specimen is performed by piling up the cross-sectional images.

Low-Cycle-Fatigue Characteristics of Short Glass Fiber Reinforced Polybuthyleneterephthalate

Two kinds of cylindrical specimens of short-glass-fiber reinforced polybuthyleneterephthalate (PBT), the one with weld line at the center (W specimens) and the other with molding direction parallel to the specimen axis (MD specimens), were fatigued under axial total-strain-controlled conditions. The fatigue life of W specimens was slightly shorter than that of MD specimens when compared at the same range of total strain, although the difference was very small. When plotted against the stress amplitude or inelastic strain energy, the fatigue life was much shorter for W specimens. The tensile peak stress in stress-strain hysteresis loops decreased with the number of cycles. Unstable fracture took place at 30 to 40% reduction of peak stress in MD specimen, while in MD specimens a sharp decrease in the peak stress and the maximum in inelastic energy took place at the 40% reduction of the tensile peak stress. Unstable fracture did not occur in W specimens. The computerized tomography (CT) using synchrotron X-rays was applied to observe nondestructively the crack growth behavior in fatigued specimens. In W specimens, crack started from the surface and extended inward as a continuous long crack, while only many small cracks observed at the central region of the specimens until unstable fracture in MD specimen.

Mechanical analysis of temperature impact on stability during superplastic tensile deformation

Based on state equation that stress is the function of strain, strain-rate and temperature, the paper establishes the differential constitutive equation used for analyzing load-stability and the variational constitutive equation used for analyzing geometry-stability during superplastic tensile deformation, which contain strain hardening index, strain-rate sensitivity index, temperature sensitivity index introducted for the first time and tempera-ture undulation index introducted for the first time in the paper. And then, based on the universal condition of plastic elementary theory, the paper analyzes load-stability and geometry-stability under continuously rising temperature and under the non-uniform tem-perature along the axes of specimen respectively. The results prove the impact of con-tinuously rising speed and non-uniform value of temperature on deformation stability is that the faster temperature rises and the more non-uniform temperature is, the smaller the corresponding uniform strain of load-stability and geometry-stability are; strain hardening index is the necessary condition of stability during superplastic tensile deformation, and geometry-instability will not happen when load-instability occurs, but happen when uniform deformation has lasted after load-instability; in the superplastic temperature field, constant temperature is not necessary condition of superplasticitiy, but during the deformation, the slower temperature rises and the more uniform temperature is, the more stable deforma-tion is.

Lack of beneficial effects of platelet‐rich plasma on sinus augmentation using a fluorohydroxyapatite or autogenous bone: an explorative study

Maxillary sinus augmentation is frequently necessary before placement of dental implants in the posterior maxilla. Besides autogenous bone graft, various bone substitutes have been used, with favourable results. Although platelet-rich plasma (PRP) has been used in the field of oral and maxillofacial surgery for years, its beneficial effects on osseous regeneration still remain unclear. The aim of this study was to evaluate the short and long time effects of PRP on single-stage sinus augmentation using autogenous bone or a fluorohydroxyapatite (Algipore) in a randomized prospective animal study. After extraction of maxillary premolars of sixteen minipigs, the wounds were allowed to heal for 2 months. Then, sinus augmentations were performed bilaterally using one of the following grafting materials: autogenous bone and Algipore with or without PRP. Three dental implants (Ankylos) were installed in each sinus simultaneously. Four animals were euthanized at each period of observation (1, 2, 8 and 12 months). Implant-bearing specimens were sectioned bucco-lingually along the long axis of implants and undecalcified ground specimens were prepared. The bone-implant-contact (BIC) was measured by means of microradiographic examination. For histological evaluation, the specimens were stained with toluidin blue, and the percentage of the newly formed bone and the remaining bone substitute were evaluated. The grafting materials chosen showed increasing levels of BIC and newly formed bone throughout the period of observation in both PRP and non-PRP groups. Adding PRP resulted in lower BIC and newly formed bone compared with autogenous bone grafts or Algipore alone. However, a statistical significance was not found. The percentages of the remaining bone substitute in both the PRP and non-PRP groups were closely comparable in all observation periods. The application of PRP could not reveal significant beneficial effects on the BIC, the percentage of the newly formed bone and the remaining bone substitute in this study.

Deformation and failure of cartilage in the tensile mode

The aim of this study was to visualize, at the ultrastructural level, the deformation and failure mechanism of cartilage matrix in the tensile mode. Full-thickness dumbbell-shaped specimens were prepared from adult bovines. There were two specimen groups; in the 'parallel' group the specimen axis was parallel to the split lines defining the preferential orientation of the collagen in the articular surface, and in the 'perpendicular' group the specimen axis was perpendicular to the split lines. Specimens were placed with the articular surface uppermost and subjected to a graded series of strain within individual mini-tension devices, while observed with stereomicroscopy and confocal laser scanning microscopy. Thereafter, the changes in the ultrastructure were observed with both scanning and transmission electron microscopy. The mechanism of cartilage failure in the tensile mode comprised the following stages, whether the strain was applied parallel or perpendicular to the split line. (1) At 0% strain a fibrillar meshwork within the articular surface was predominantly orientated in the direction of the split line. (2) As strain increased, the fibrillar meshwork became more orientated in the parallel group and reorientated in the perpendicular group in the direction of the applied strain. (3) After complete reorientation of the fibrillar meshwork in the direction of the applied strain, the initial sign of failure was rupture of the fibrillar meshwork within the articular surface. (4) Subsequently, the rupture rapidly propagated into the deeper layers. Greater strains were required for fibrillar reorientation and complete rupture in the 'perpendicular group' than in the parallel group.

Load-fatigue performance of gold crowns luted with resin cements

Resin cements have gained popularity over the past few years because of their improved physical properties. There is a need to test these cements under fatigue loading, as there is growing recognition that fatigue testing is more clinically relevant than traditional monotonic static tests. This study investigated the load-fatigue performance of complete gold crowns cemented with 4 types of resin cement. Four resin cements (C & B Opaque [CBO], Calibra Esthetic [CE], RelyX Unicem [RU], and Panavia F [PF]) and a control, zinc phosphate cement (HY-Bond [HBZPC]) were tested. Fifty human maxillary premolars were prepared to an occluso-cervical dimension of 4 mm and a convergence angle of 20 degrees. Complete gold crowns were cast (Strator 3) and cemented with 1 of the 5 cements (n=10). A fatigue load of 73.5 N was applied at an angle of 135 degrees to the long axis of each tooth-crown specimen. Preliminary failure was defined as the propagation of a crack in or around the crown luting cement layer. The number of cycles to preliminary failure and the cement failure location were determined. Significant differences in cycles to preliminary failure were assessed by the nonparametric Kruskal-Wallis test, with follow-up Mann-Whitney tests (alpha=.05). Group CE had the highest rank of cycles to preliminary failure, while HBZPC had the lowest cycles to preliminary failure. Group CE had a significantly higher failure cycle count compared to PF (P=.016), RU (P=.001), and HBZPC (P<.001), but was not significantly different from CBO (P=.112). There was no significant difference in the failure cycle count between RU and HBZPC (P=.070). Not all tested resin cements had a superior fatigue life when compared with zinc phosphate cement. Of the 4 resin cement groups, Groups CE, CBO, and PF were significantly superior to HBZPC.

Crack Growth Behavior of Al Alloy 7075-T6 under Ultrasonic Fatigue

In order to investigate the effect of frequency on the crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy, 7075-T 6, in ambient air and in N2 gas, and the results were compared with those in rotating bending fatigue. Fatigue strength was higher in ultrasonic fatigue than in rotating bending one. This was caused by the retardation of a crack initiation and its early propagation. In ultrasonic fatigue, the growth direction of a crack changed macroscopically from a tensile mode to a shear one which the direction was about 35 degrees against to the specimen axis, and fracture mechanism also changed from striations to transgranular facets with voids microscopically. Crack growth rate at the transition of crack growth direction was about 3 × 10-9 m/cycle. The relation between an applied stress σa and a crack depth at the transition of crack growth direction bT was expressed by σnabT=constant. These results were explained from the time dependent environmental effect and texture of microstructure.

412 時効硬化Al合金の超音波疲労における破壊機構(OS4(1) エネルギー・環境負荷低減機器・材料の強度)

In order to investigate the effect of frequency on the crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy, 7075-T6, in ambient air and in N_2 gas, and the results were compared with those in rotating bending fatigue. In ultrasonic fatigue, the growth direction of a crack changed macroscopically from a tensile mode to a shear one which the direction was about 35 degrees against to the specimen axis, and fracture mechanism also changed from striations to transgranular facets with voids microscopically. Crack growth rate at the transition of crack growth direction was about 3×10^<-9>m/cycle. These results were explained from the time dependent environmental effect and texture of microstructure.

4056 SUJ2におけるせん断型疲労き裂進展(G03-12 き裂進展(1),G03 材料力学)

Growth behaviour of shear-type fatigue crack in a bearing steel, JIS SUJ2, was investigated by a biaxial fatigue testing machine using round specimens. Either following two kinds of defect with total length 400〜440μm and depth 200-300μm was introduced into specimen surface ; (1) a semi-elliptical pre-crack emanating from a 2-hole defect by a tension-compression loading, (2) a 3-hole defect oriented in the axial direction which has FIB slits at the edge of the defect. Fully reversed torsion corresponding to shearing stress amplitude at specimen surface, τ_a=600MPa, was applied to each specimen under static compressive stress σ_m=-1000〜-1200MPa. In case of defect (1), a shear-type crack propagated from the pre-crack in direction perpendicular to the specimen axis. At the specimen surface, the shear-type crack periodically branched from the crack tip and propagated 5〜10μm in Mode I directions. The shear-type crack growth was decelerated with the increase in the crack length and finally stopped at N&cong;7.5×10^6 cycles and 2a&cong;600μm. On the other hand, in case of defect (2), the shear-type crack propagated in axial direction, and the crack growth was accelerated with the increase in the crack length. These results revealed that friction between crack faces is a strong resistance in the shear-type crack growth.

Fracture energy of concrete at high loading rates in tension

The effect of high loading rates in tension on the failure energy and strength of concrete is reported in this paper. High loading rates exceeding 5000 GPa/s corresponding to strain rates higher than ∼120 s −1 can be applied by use of Hopkinson bar set-up designed to produce spall. Tension tests were performed on cylindrical specimens made of micro-concrete. At high loading rates, or strain rates, the failure energy of micro-concrete, as well as the strength, was found to substantially increase. It was also found that the material humidity has only a small effect on the failure energy of micro-concrete in the range of high loading rates. On the other hand, post-mortem optical analysis of the fractured surfaces of specimens indicated that almost all the population of aggregates, and not only the matrix, was fractured on the same surface perpendicular to the specimen axis. Such observations suggest that the substantial increase of the failure energy and strength in dynamic tension is caused by multiple micro-cracks, which propagate at the same time on the fracture plane. The mechanism of multiple micro-cracking triggered within the short loading time characteristic of high loading rates needs a high energy input in order to create the fracture surface, leading to the observed increase in strength.

Finite element simulation of PSB macroband nucleation and propagation in single crystal nickel cycled at low plastic strain amplitudes

Substructure models for vein matrix and persistent slip band (PSB) structures are extracted from a uniaxial mixtures model that was developed to simulate cyclic loading experiments on nickel single crystals oriented for single slip. Reverse magnetostriction is included as well. These substructure models are implanted in a single crystal plasticity framework with fully anisotropic elasticity. The resulting constitutive models are incorporated in finite element models to simulate the process of PSB macroband formation and propagation. Perturbation elements (PEs), elements assigned with PSB properties, are used as the loci for PSB macroband nucleation. Transition of elements with vein matrix properties to elements with PSB properties is triggered at integration points by a shear stress criterion applied on slip systems. The resulting finite element models successfully demonstrate the process of PSB formation and propagation, and plastic strain amplitude partitioning between vein matrix and PSB macrobands. The effect of model boundary constraints, strain increment dependence, mesh sensitivity, PE distribution, specimen axis misorientation, and PSB volume fraction generated is examined.

A Unified Method for the Prediction of the Fatigue Strength of Small-Hole-Containing Components under Combined Loading

A unified method is presented for the prediction of the fatigue strength of steel components containing small holes and being subjected to combined loading. Materials investigated were an annealed 0.37% carbon steel and a quenched and tempered Cr-Mo steel. Combined axial and torsional fatigue loading tests were carried out using specimens containing a small hole, which was introduced into the surface by drilling. The diameter of holes equaled the depth and was either 100µm or 500µm. The non-propagating cracks emanating in the radial direction from the holes were observed at the fatigue limit. When the loading condition is the same, they were on a plane that inclined at the same angle with respect to the specimen axis, regardless of the size of holes. This result suggested that the fatigue strength would be controlled by the Mode I threshold condition for propagation of a crack initiated on a critical plane. A criterion connecting uniaxial fatigue strength with multiaxial fatigue strength was proposed based upon the assumption that at the threshold level, the variation of the stress intensity factor of a Mode I crack initiated under combined loading equaled that under uniaxial loading. The predictive method proposed based upon this criterion is practical in that no fatigue test is necessary in making predictions. For the various conditions of in-phase and out-of-phase fatigue loadings with an imposed mean or static load, experimental results agreed well with predictions.