Unidirectional Tests Research Articles

Fractal Characterization of Relative Movement Modes in Simulated Friction and Wear Tests

The selection of the relative movement mode between the friction pairs in simulated friction and wear tests is a crucial factor for the characterization and evaluation of metallic material properties. In this study, two kinds of commonly used metal materials (stainless steel 0Cr18Ni9 and aluminum alloy 2A12) were applied for the simulated friction and wear tests with four different modes of relative motion, including unidirectional, reciprocating, circular and multi-directional cross-shear. The corresponding surface topography and statistical parameters such as surface roughness Ra were obtained via OLYMPUS ultra-depth microscope. Based on the fractal theory, fractal dimension D was calculated to characterize the surface topography and the results indicate that, the fractal dimension D of the unidirectional and multi-directional cross-shear simulated friction and wear tests is the minimum and maximum respectively, which reflects that the fractal dimension D is able to characterize the complexity of the surface morphology. The fractal dimension D may be related to the intrinsic physical properties of metal materials, such as hardness and toughness, which needs to be further studied.

Analysis of MrI Image to Develop the Aid During the radiological Test of Femoro Acetabular Impingement

Background/Objectives: It is to sustain the test accuracy and improve diagnostic capability of selfdevelopedaid in Dunn view to confirm modification of pistol grip in neck of femur that causes anteriorfemoro acetabular impingement.Method/Statistical Analysis: The test was performed before and after the usage of the self-developed aidin the patients referred to the test of Dunn view (45 and 90-degree flexion) who were scheduled with hiparthroscopy. ?-angle and femoral head–neck offset were measured by oblique transverse images in MRI testand statistical significance was analyzed with paired T-test.Findings: In the MRI images and Dunn 45° and 90° images before and after ancillary device use, as a resultof measuring and analyzing ?-angle, it was not statistically significant at 45° (P>0.05), but it was foundthere was statistical significance in 90° (P<0.05). In the MRI images and Dunn 45° and 90° images beforeand after ancillary device use, as a result of measuring and analyzing femoral head-neck offset, it was foundthere was statistical significance in both 45° and 90° (P<0.05).Improvements/Applications: Upon the comparison results of unidirectional image and MRI test beforeand after the use of the aid in this study, statistically significant outcomes were found in 45 and 90 degree ofDunn view after the use of the aid. Therefore, it is considered that they could be used as the foundation datain the image studies with Dunn view.

The response of suction caissons to multidirectional lateral cyclic loading in sand over clay

Offshore wind turbines and their foundations experience loading from varying directions, yet understanding of the effect of changes in the direction of applied cyclic loading on foundation response remains limited. This study investigates the behaviour of a suction caisson foundation in sand over clay under various types of multidirectional cyclic loading. The findings are significant: although the caisson rotation (or tilt) is affected by changes in load direction, the caisson rotation is less than that in a unidirectional test with the same cyclic load magnitude and symmetry, meaning that a unidirectional test may serve as a conservative estimate of caisson rotation for multidirectional loading. This contrasts with previous findings for monopiles in sand, where prediction of the accumulated displacement based on unidirectional cyclic loading was substantially un-conservative for multidirectional loading. Changes in unloading stiffness due to changes in load direction are slight, varying by an amount that is no greater than the change measured over the course of a unidirectional test. Foundation stiffness and ultimate capacity following multidirectional cyclic loading are largely unaffected, unlike unidirectional cyclic loading, where consolidation of the clay layer improves both the stiffness and capacity.

Monotonic and hysteretic in-plane behaviour of graphene through an atomistic FE model

This paper presents a computational study on the monotonic and hysteretic in-plane behaviour of graphene. With this purpose, atomistic finite element models of graphene were developed taking into account the degradation of stiffness and strength through an elastic-plastic model. The study extends the typical unidirectional tests (in armchair and zigzag directions) to the bidirectional test and the shear test, establishing a consistent and comprehensive set of both elastic and strength properties. The mechanical properties obtained from the monotonic analyses (elastic and strength properties) are validated from the comparison with those available in the literature (experimental, density functional theory, molecular dynamic simulations and finite element models). The strain-softening behaviour of graphene is assessed through these atomistic models. The failure modes of graphene sheets in different loading tests are detailed and its load carrying capacity is explained. Finally, the hysteretic behaviour of graphene is discussed. The stress-strain curves and the variation of dissipated energy with the strain are given for different number of cycles. Then, some concluding remarks are drawn.

Indoor direct shear and uniaxial compression testing of polymer-modified silt

Silt samples modified with a polymer [polyacrylamide (PAM)] and sodium silicate were tested before and after immersion through direct shear and unidirectional compression tests to determine shear strength and compression deformation characteristics. The cohesion and internal friction angle of these modified silt samples were significantly higher. These modified silt samples also exhibited better water resistance and their degrees of compression deformation were small. After water immersion, the degree of condensation polymerization of PAM was lowered, the strength of the modified silt decreased, and the degree of compression deformation increased. It is slightly different with silt modified with sodium silicate.

Impaired Maintenance of Interpersonal Synchronization in Musical Improvisations of Patients with Borderline Personality Disorder.

Borderline personality disorder (BPD) is a serious and complex mental disorder with a lifetime prevalence of 5.9%, characterized by pervasive difficulties with emotion regulation, impulse control, and instability in interpersonal relationships and self-image. Impairments in interpersonal functioning have always been a prominent characteristic of BPD, indicating a need for research to identify the specific interpersonal processes that are problematic for diagnosed individuals. Previous research has concentrated on self-report questionnaires, unidirectional tests, and experimental paradigms wherein the exchange of social signals between individuals was not the focus. We propose joint musical improvisation as an alternative method to investigate interpersonal processes. Using a novel, carefully planned, ABA′ accompaniment paradigm, and taking into account the possible influences of mood, psychotropic medication, general attachment, and musical sophistication, we recorded piano improvisations of 16 BPD patients and 12 matched healthy controls. We hypothesized that the insecure attachment system associated with BPD would be activated in the joint improvisation and manifest in measures of timing behavior. Results indicated that a logistic regression model, built on differences in timing deviations, predicted diagnosis with 82% success. More specifically, over the course of the improvisation B section (freer improvisation), controls' timing deviations decreased (temporal synchrony became more precise) whereas that of the patients with BPD did not, confirming our hypothesis. These findings are in accordance with previous research, where BPD is characterized by difficulties in attachment relationships such as maintaining strong attachment with others, but it is novel to find empirical evidence of such issues in joint musical improvisation. We suggest further longitudinal research within the field of music therapy, to study how recovery of these timing habits are related to attachment experiences and interpersonal functioning in general.

A Characterization for the Deformation Behavior of As-Cast P91 Alloy Steel and Utilization in Hot Extrusion Process

The constitutive models of as-cast P91 alloy steel were investigated by unidirectional thermal compression tests, which were conducted over a wide range of temperature and strain rate on Gleeble-3500 thermal simulation machine. The constitutive models were coupled with finite element method to simulate the hot extrusion process. Furthermore, the industrial hot extrusion experiment on actual pipe was conducted on 500 MN vertical extrusion machine and the load-displacement data during the extrusion were recorded. Comparisons between the numerical simulation and industrial experimental results were carried out and confirmed that the developed constitutive models can be used in the simulation and industrial research of compact hot extrusion process.

Sample Size Effect of Magnetomechanical Response for Magnetic Elastomers by Using Permanent Magnets

The size effect of magnetomechanical response of chemically cross-linked disk shaped magnetic elastomers placed on a permanent magnet has been investigated by unidirectional compression tests. A cylindrical permanent magnet with a size of 35 mm in diameter and 15 mm in height was used to create the magnetic field. The magnetic field strength was approximately 420 mT at the center of the upper surface of the magnet. The diameter of the magnetoelastic polymer disks was varied from 14 mm to 35 mm, whereas the height was kept constant (5 mm) in the undeformed state. We have studied the influence of the disk diameter on the stress-strain behavior of the magnetoelastic in the presence and in the lack of magnetic field. It was found that the smallest magnetic elastomer with 14 mm diameter did not exhibit measurable magnetomechanical response due to magnetic field. On the opposite, the magnetic elastomers with diameters larger than 30 mm contracted in the direction parallel to the mechanical stress and largely elongated in the perpendicular direction. An explanation is put forward to interpret this size-dependent behavior by taking into account the nonuniform field distribution of magnetic field produced by the permanent magnet.

Experimental and numerical investigation of fatigue damage accumulation in composite laminates

In this study, a three-dimensional finite element model was developed to predict the fatigue life of composite bolted joints. In this model, progressive damage theory was used. The fatigue characterization was based on Hashin’s failure criteria which recognize the failure modes. To decrease the number of unidirectional tests, the effects of load ratio were considered based on Kawai’s criterion. A modified form of Miner’s rule was proposed to calculate the damage parameter. This equation corrected the effects of the fatigue failure cycles and included the effects of different load ratios. Also, this model could decrease the overestimation of the fatigue life predictions. All of the formulations were combined and used in a step-by-step solution. In this respect, a new iterative algorithm was developed so that at each step of solution, the material properties of all failed layers of each element were reduced according to the failure mode and sudden degradation rules. The estimated fatigue life was compared to the experimental data, and an excellent correlation between the results was observed. This model could monitor the damage propagation in fabricated joints.

Determination of in-plane elastic constants of angle ply laminates from tensile measurements

This paper presents a new method to completely characterise the in-plane elastic properties of an important type of angle ply laminates using only unidirectional tests. The angle ply laminates having the same number of identical plies are considered. Some new results for orthotropic laminates are found using this technique, namely, the conditions of existence of a particular direction in which there is no shear extension coupling. The laminates are subjected to three tensile tests: two in the orthotropic axes and the third one in a particular direction. The results allow a complete semiexperimental characterisation of the angle ply laminate, which do not need a priori knowledge of the elastic properties of the constitutive layer. Comparisons are made between numerical predictions and experimental results. Finally, the computational results were compared to the experimental results, verifying the capability of the method in order to predict the in-plane elastic properties of composite laminates.

Generalization of the memory integer model for the analysis of the quasi-static behaviour of polyurethane foams

Polyurethane foam is a cellular material characterized by an interesting mechanical spectrum of properties: low density, capacity to absorb the deformation energy and low stiffness. This spectrum of properties makes polyurethane foam commonly used in many thermal, acoustic and comfort applications. Several models, such as memory, hyper-elastic and pseudo-elastic models have been developed in the literature to describe the mechanical response of polyurethane foam under quasi-static and dynamic test conditions. The main disadvantage of these models is the dependence of their parameters against the test conditions (strain rate, maximum compression level, etc). This affects the general character of their representativeness to the quasi-static and dynamic behaviours of polyurethane foam. The main goal of this article is to implement reliable mechanical model which is able to provide the quasi-static response of the polyurethane foam under different strain rates and large compressive deformation. The dimensional parameters of our model can be expressed by the product of two independent parts; the first contain only the test conditions and the second define the dimensionless and invariant parameters that characterize the foam material. The developed model has been proposed after several experimental studies allowing the apprehension of the quasi-static behaviour (through unidirectional compression tests). The polyurethane foam, under large deformations, exhibits a nonlinear elastic behaviour and viscoelastic behaviour. To assess the ability of our model to be a general representation, three industrial polyurethane foams have been considered.

The Shear Properties of DP980 High Strength Steel Plate

In this study, the high strength steel DP980 material shear properties were investigated. In the design process, first of all based on literature paper and test specimen optimal size requirements, and then find ways to meet the current test equipment maximum capacity (100 kN). The Studies completed DP980 1.4 mm specimens of tensile test, one-way shear test and forward and reverse shear loading experiments. Limited by the maximum output of the machine capacity 100 kN, the thickness 1.4 mm steel plate with strain gage measurements under unidirectional force generated by experiments at the maximum shear strain of 9.890%. And the forward and reverse biased loading method, the completion of seven Bauschinger shear stress-shear strain curves. In the unidirectional shear test results, first verify that the elastic region of the shear elastic modulus of 74.7 GPa, in line with the basic properties of steel materials. Then the shear stress-shear strain curve is converted to stress-strain curve relationship. Wherein the shear stress-shear plastic portion of the curve was converted by factor 1.81, there is overlap between the tensile and shear experimental results confirm rationality.

The effect of transient conditions on synovial fluid protein aggregation lubrication

Little is known about the prevailing lubrication mechanisms in artificial articular joints and the way in which these mechanisms determine implant performance. The authors propose that interfacial film formation is determined by rheological changes local to the contact and is driven by aggregation of synovial fluid proteins within the contact inlet region. A direct relationship between contact film thickness and size of the protein aggregation within the inlet region has been observed.In this paper the latest experimental observations of the protein aggregation mechanism are presented for conditions which more closely mimic joint kinematics and loading. Lubricant films were measured for a series of bovine calf serum solutions for CoCrMo femoral component sliding against a glass disc. An optical interferometric apparatus was employed to study the effects of transient motion on lubricant film formation. Central film thickness was measured as a function of time for a series of transient entrainment conditions; start-up motion, steady-state and non-steady-state uni-directional sliding, and bi-directional sliding. The size of the inlet aggregations was found to be dependent upon the type of transient condition. Thick protective protein films were observed to build up within the main contact region for all uni-directional tests. In contrast the inlet aggregation was not observed for bi-directional tests. Contact film thickness and wear was found to be directly proportional to the presence of the inlet protein phase. The inlet phase and contact films were found to be fragile when disrupted by surface scratches or subjected to reversal of the sliding direction.

Evaluation of in-plane ply shear properties from unidirectional plate torsion tests

Torsion tests were conducted on unidirectional carbon/epoxy laminated plates. Preliminary finite element analyses showed that the specimen geometry selected avoided pronounced geometric non-linearity and ensured that a significant volume of material would be under a high fraction of the maximum shear stress. Furthermore, the clear prevalence of in-plane shear stresses allowed the development of a simplified data analysis model. Calculated shear-stress strain curves were consistent with the results of tensile tests on angle-ply coupons, despite lower failure stresses that may have been caused by surface defects or by spurious transverse tensile stresses. Nevertheless, the unidirectional plate torsion test is worthy of further research, given the structural relevance of torsional loads and the problems of in-plane shear tests methods.

Resistance of Short, Stiff Piles to Multidirectional Lateral Loadings

Abstract Lateral loads applied to pile foundations in some cases are multidirectional. However, most of the past studies only considered soil-pile interaction under unidirectional horizontal loadings. This paper describes a comprehensive experimental study on a pile-sand system under both unidirectional and multidirectional horizontal loadings using a computer numerically controlled biaxial motion platform. The displacement paths at the pile head include unidirectional regular paths, cross paths, figure-8 paths, and unidirectional and multidirectional irregular paths with different displacement amplitudes and different aspect ratios of the displacement amplitudes along two horizontal directions (α). The test results indicate that the preloading along one horizontal direction influences the subsequent response along the orthogonal horizontal direction, in terms of the pile resistance and the direction of the force increment vector. In the figure-8 tests, the shapes of the force-displacement curves in most cases differ significantly from that obtained from the unidirectional regular test and different from the unidirectional regular test, the maximum forces appear before the displacements reach the maximum values. In these tests, the direction of the force increment vector always deviates from the direction of the displacement increment vector. According to the results of the regular and irregular loading tests, the lateral resistance of the pile under the multidirectional paths is generally lower than that under the unidirectional path, and the degree of reduction increases with the aspect ratio (α). The ratio of force (rF), defined as the maximum force in the multidirectional tests to that in the unidirectional test, can be expressed as an exponential function of α. Considering that the reduction in the resistance can reach as large as about 30%, overlooking the multidirectional loading effect can lead to unconservative analysis or design in some cases.

Application of residual strength models to finite element analysis in fatigue life estimation of a composite wing spar

An engineering approach is proposed to assess fatigue life of an aircraft composite wing spar. Two different strength degradation models are validated using finite element simulation. Stiffness degradation data is obtained based on unidirectional coupon test results from the literature. A code in the finite element software ANSYS is written that lowers the strength and stiffness in each cycle. Stress redistribution is found in any cycle using new stiffness data, and the model is checked for failure. In order to verify the model, bending fatigue tests are carried out on an unmanned aircraft spar sample. The more accurate model is used in fatigue life assessment of the spar under service loading that is found using MINITWIST algorithm. The results indicate that the proposed approach can be used for design engineers in fatigue life assessment of composite wing structures.

필라멘트 와인딩 탄소섬유 복합재의 인장강도 크기 효과

This paper presents the results of theoretical analysis and experimental test to show the size effect on the fiber strength of filament would pressure vessel. First, a series of fully scaled hoop ring tests with filament would carbon-epoxy were conducted, which exhibited a remarkable size effect on the fiber strength. Next, the failure analyses using WWLM(Weibull Weakest Link Model) and the SMFM(Sequential Multi-step Failure Model) were performed and compared to the hoop ring test data, as well as to unidirectional specimens test data from the literature. It was found that the analysis results significantly underestimated the fiber strengths compared to the test data. In this study, a modified SMFM was proposed through the modification of the length size effect. The fiber strengths from modified SMFM analysis showed good agreement with the test data.

Uni- and multidirectional wear resistance of different crosslinking degrees in UHMWPE for artificial joints

The aim of this work was to study the effect of UHMWPE crosslinking on wear performance. Differently treated UHMWPEs were studied by means of unidirectional and multidirectional wear tests. Unidirectional tests simulate total knee replacement and multidirectional tests simulate total hip replacement movements. The samples tested were observed by optical and scanning electron microscopy in order to determine wear mechanisms that explain the different results obtained in the uni- and multidirectional wear tests performed.

Rapid Assessment of Age-Related Differences in Standing Balance

As life expectancy continues to rise, in the future there will be an increasing number of older people prone to falling. Accordingly, there is an urgent need for comprehensive testing of older individuals to collect data and to identify possible risk factors for falling. Here we use a low-cost force platform to rapidly assess deficits in balance under various conditions. We tested 21 healthy older adults and 24 young adults during static stance, unidirectional and rotational displacement of their centre of pressure (COP). We found an age-related increase in postural sway during quiet standing and a reduction of maximal COP displacement in unidirectional and rotational displacement tests. Our data show that even low-cost computerized assessment tools allow for the comprehensive testing of balance performance in older subjects.

Deliberation of Effect to Glass Imprinting Analysis by Williams-Landel-Ferry Equation

The Mems-ONE is well known software which simulates thermo-viscoelastic properties in the conduct of nanoimprinting. Assuming the glass materials to be viscoelastic body, the relaxation shear modulus was measured by the creep test, Williams-Landel-Ferry (WLF) equation is applied for expressing the temperature dependence of liquid viscosity. We compared experimental with analytic results used by Mems-ONE with the condition of fixed pressure and time. Thermo-viscoelastic properties of the glass materials were estimated using unidirectional compression creep test based on traditional thermo viscoelastic theory. Glass was Borosilicate Glass (D263, Schott). Glass imprinting was carried out on Glassy Carbon (GC) mold with line & space10 μm patterns fabricated by dicing saw. The machining accuracy is most important thing as the evaluation mold. The glass imprinting temperature consulted thermo-viscoelastic properties of the glass materials. The numerical simulation was carried out on the small portion of mold and glass. The constant value of WLF equation fitting in high temperature translates the master curve of D263 with a high degree of accuracy. It caused the accuracy improvement of analysis result. In addition, we confirm that WLF equation intended to resin can use to the glass imprinting.