Influence Of Specimen Geometry Research Articles

Influence of Specimen Geometries on the Viscoelastic Properties of Bituminous Mixtures in Torsion

A standard test method for determining the linear viscoelastic properties of bituminous mixtures in torsion prescribes the use of a dynamic shear rheometer. The method uses a prismoidal specimen (rectangular cross section) sliced from a Superpave gyratory compacted sample. However, the geometry utilized in the standard is a non-axisymmetric cross section, which leads to the development of warping stress when the specimen is tested in torsion using a dynamic shear rheometer. On the other hand, axisymmetric geometry, such as cylinder (circular cross section), does not warp when subjected to torsion. This study investigates the influence of the two specimen geometries, namely prismoidal and cylindrical, on the linear viscoelastic properties of bituminous mixtures in torsion. The specimens are obtained from a bituminous mixture with a nominal maximum aggregate size of 13.2 mm, and statistical analysis is carried out to determine whether the material constitution in the specimen geometries is identical. A frequency sweep experiment is conducted at 10, 20, and 30°C with a constant strain amplitude of 0.001% in the frequency range of 0.01 Hz to 20 Hz. The absolute shear modulus of the prismoidal specimens is found to be higher than that of cylindrical specimens because of warping stresses in prismoidal specimens. It was seen that the effect of warping stress is greater at higher temperatures and lower frequencies. Correction factors are used to correct the absolute shear modulus of prismoidal specimens. These findings highlight the importance of considering correction factors for warping when characterizing prismoidal bituminous mixtures in torsion.

Influence of specimen geometry and notch on fatigue lifetime and fracture behavior of aluminum-based nanocomposite under stress-controlled fully-reversed bending loads.

In the present article, the effect of the specimen geometry and the sample notch was studied on the high cycle fatigue lifetime and fracture behavior of the aluminum-based nanocomposite. For such an objective, rotary fully-reversed bending fatigue tests were performed on smooth and notched specimens, with the frequency of 100 Hz. Then, simulated results using the MSC Fatigue software were calculated and compared to the fatigue lifetime in the experiments for validation. Moreover, scanning electron microscopy was utilized to observe the fracture surface of failed samples after testing. Obtained results indicated that the fatigue lifetime increased by enhancing the sample diameter. However, the fatigue lifetime reduced when the stress concentration factor changed from 1.0 to 2.9. All samples with three geometries had a brittle fracture due to cleavage and quasi-cleavage marks on the fracture surface.

Influence of specimen geometry on the energy release rate in concrete

The energy release rate during the crack propagation in concrete was studied using three-point bending (TPB) beams with different geometries. Expressions for determining the energy release rate were established. A total of 44 beams, i.e., TPB specimens with the height of 150 mm and various spans and the same span of 800 m but different heights, named as Series-T and Series-TH, respectively, were tested. The obtained results reveal that (1) with the crack propagation, the energy release rate curves (GR-curves) monotonically increased and convergence to the fracture energy of each specimen, and the average values were 161.136 N/m and 112.343 N/m for Series-T and Series-TH. (2) For Series-T, with increasing the specimen span from 300 mm to 900 mm, the maximum fracture process zone (FPZ) length kept constant of 68.317 mm, and for Series-TH, the result increased by 187.6 % with increasing the specimen height from 100 mm to 300 mm. Moreover, the relative FPZ length was not affected by the spans and depths of the specimens. (3) The evolution of crack tip opening displacement was only affected by the specimen ligament length, i.e. for the same crack extension length, a larger value was noticed for longer ligament length. (4) The stability during crack propagation can be analyzed using GR-curves.

Influence of specimen geometry on torsion of bituminous mixtures

This investigation focuses on the measurement of linear viscoelastic properties of the bituminous mixture using different specimen geometries in Dynamic Shear Rheometer (DSR). Two different specimen geometries, cylindrical and prismoidal (rectangular cross-section) specimens are used for testing in torsion. The cylindrical specimen of 12 mm diameter and prismoidal specimen with width to thickness ratio of 1.3 are used in the study. The length of both specimen geometries is restricted to 50 mm. The linear viscoelastic limit for the bituminous mixtures was estimated by performing an amplitude sweep experiment. The linear viscoelastic parameters are measured using a strain amplitude of 0.001 % and at frequencies ranging from 45 to 0.1 Hz. The results show the difference in the linear viscoelastic parameters measured using cylindrical and rectangular specimens i.e., the absolute shear modulus of the prismoidal specimen is greater than the cylindrical specimen. Such an increase in absolute shear modulus is because of the end restraint in torsion for prismoidal specimen i.e., warping. This study has documented such results for a range of temperatures and frequencies. The difference in the linear viscoelastic properties is found to be insignificant at 15 °C for the frequencies above 0.5 Hz and predominant at 35 and 55 °C for all the frequencies. The absolute shear modulus of bituminous mixtures for prismoidal specimens is computed and it is seen that the difference in absolute shear modulus is contributed predominantly due to the restriction of the warping in the prismoidal specimen due to the end restraint. This study shows the necessity for the correction of the absolute shear modulus of the bituminous mixture measured using prismoidal specimen for a given aspect ratio.

Influence of Specimen Geometry and Notch on Hydrogen Embrittlement Resistance of SA372 Steel for Pressure Vessel

Influence of Specimen Geometry and Notch on Hydrogen Embrittlement Resistance of SA372 Steel for Pressure Vessel

Effect of plastic strain and specimen geometry on plastic strain ratio values for various materials

The aim of this paper is to show influence of two elements on plastic strain ratio value, or "r" value. The first element is value of plastic strain, and second is specimen geometry. Extensive experiment was conducted according to appropriate tensile test procedure with 3 materials and 5 different specimen geometries. Steel sheet S235JR, austenitic stainless-steel sheet X5CrNi18-10 and Al alloy sheet AlSi0.9MgMn (i.e. ENAW 6081) were used during the experiments. Nominal thickness for all three sheets was 1 mm. Three out of five specimen geometries had 20 mm width and gage length of 60, 120 and 160 mm while the rest of specimens had width of 15 mm and gage length of 50, 100 mm. All the specimens were laser cut in rolling direction. In preparation part of the experiment, behind material characterization (obtaining base mechanical properties) identification of homogenous deformation field was performed, i.e. plastic strain at the beginning of localization, for each specimen. Related to that strain value 6 degrees of deformation were realized: 75%, 80%, 85%, 90%, 95% and 100%. Results showed expected and significant difference in "r" value for used materials, but influence of specimen geometry and realized plastic strains were low.

Effect of plastic strain and specimen geometry on plastic strain ratio values for various materials

The aim of this paper is to show influence of two elements on plastic strain ratio value, or "r" value. The first element is value of plastic strain, and second is specimen geometry. Extensive experiment was conducted according to appropriate tensile test procedure with 3 materials and 5 different specimen geometries. Steel sheet S235JR, austenitic stainless-steel sheet X5CrNi18-10 and Al alloy sheet AlSi0.9MgMn (i.e. ENAW 6081) were used during the experiments. Nominal thickness for all three sheets was 1 mm. Three out of five specimen geometries had 20 mm width and gage length of 60, 120 and 160 mm while the rest of specimens had width of 15 mm and gage length of 50, 100 mm. All the specimens were laser cut in rolling direction. In preparation part of the experiment, behind material characterization (obtaining base mechanical properties) identification of homogenous deformation field was performed, i.e. plastic strain at the beginning of localization, for each specimen. Related to that strain value 6 degrees of deformation were realized: 75%, 80%, 85%, 90%, 95% and 100%. Results showed expected and significant difference in "r" value for used materials, but influence of specimen geometry and realized plastic strains were low.

Solutions and applications of 3D elastic–plastic constraint parameters for clamped single edge notched tension (SENT) specimens

Single edge notched tension (SENT) specimen is a common fracture toughness test specimen now widely used in the pipeline and pressure vessels industries. In this paper, an extensive study has been conducted by three-dimensional (3D) finite element analyses (FEAs) to investigate the in-plane constraint parameters (namely A and QSSY) and out-of-plane constraint parameter, that is, Eε33 for clamped SENT specimens with side-grooves. A wide range of crack depth to specimen width ratios a/W = 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7, specimen thickness to specimen width ratios B/W = 0.5, 1.0, 1.5, 2.0, 3.0 and 4.0 were included. The various strain hardening exponent (n = 4, 7, 10) and applied loading levels (from small-scale yielding to large-scale yielding) were also investigated. The results show that the effects of crack depth, specimen thickness, loading level and strain hardening index on the 3D constraint parameters show a significant coupling effect. With the increase of load level, A value increases monotonically, while QSSY and the normalized Eε33 (called V33) decrease, and the influence of specimen geometry on the constraint levels will become greater. The values of A and V33 obviously decrease with the increase of hardening exponent, but the change of QSSY is relatively small. Moreover, it can be observed that both A and QSSY can well describe the in-plane constraint effect, and V33 can better quantify the out-of-plane constraint effect under varying loading levels and n. In addition, elastic–plastic constraint parameters were also calculated for various experimental test specimens made of 16MND5 steel, with n = 9.2. It was demonstrated these constraint parameters can be applied to quantify and predict the J-R curves of 16MND5 steel with good agreements for specimens with different in-plane and out-of-plane constraint conditions.

Maximum resistance rate principle for quasi-brittle fracture

The maximum resistance rate principle (MRRP) is proposed to characterise the unstable of quasi-brittle fracture. Under quasi-static loading conditions, the unstable fracture of quasi-brittle materials occurs when the resistance rate reaches its maximum value. Firstly, the whole fracture process of the single edge cracked specimen was calculated, and the MRRP was elaborated based on the calculated fracture resistance and resistance rate curve. Then, the MRRP was verified by existing experimental data of three-point bending beams of different sizes. Furthermore, the influence of specimen geometry, size and material parameters on the fracture resistance and resistance rate was discussed. The calculation results reveal that the resistance rate and external load reach their maximum values in the critical state simultaneously. Combined with the cohesive crack model, the MRRP can well describe the unstable fracture of quasi-brittle materials, which is an extension of Griffith’s theory of brittle fracture.

The Influence of Specimen Geometry and Loading Conditions on the Mechanical Properties of Porous Brittle Media

Dynamic tests of fine-grained fired dioxide-zirconia ceramics under compression under uniaxial stress conditions were carried out. The influence of the specimen length on the obtained strength and deformation properties of ceramics is investigated. The thickness of the specimen has a significant impact on the course of the obtained dynamic stress–strain diagrams: short specimens have a much more sloping area of active loading branch. The main contribution to the modulus of the load branch resulting from tests of brittle porous media is made by the geometry of the specimens and the porosity of the material. When choosing the length of specimens for dynamic tests, the optimal geometry of the tested specimens is preferable in accordance with the Davies–Hunter criterion, when the contributions of axial and radial inertia are mutually compensated, and the contribution of the effects of friction in the resulting diagram is minimal. When choosing the geometry of specimens of brittle porous media, the structure of the material should be taken into account so that the size of the specimen (both length and diameter) exceeds the size of the internal fractions of the material by at least five times.

Influence of specimen geometry on fracture toughnesses of concrete based on boundary effect model

This paper presents the effect of specimen geometry on fracture characteristics of concrete in terms of fracture toughness KIc and initial fracture toughness KIcini. Three commonly used specimen geometries in laboratory were adopted in the study, that is, three-point bending (TPB), compact tension (CT) and four-point bending (FPB) specimens. The Boundary Effect Model (BEM) was used to determine these two fracture parameters, where a new approach was proposed to derive KIcini. To do this, only the maximum aggregate size dmax, the maximum load Pmax and the initial crack length relative to the specimen depth α0 were required. Previous experiments from TPB, CT and FPB specimens were reutilized to acquire KIc and KIcini, and then the geometry influence on these two fracture toughnesses were investigated. The results show that the gained values of KIc and KIcini from TPB, CT, FPB separately or combined TPB + CT + FPB were rather close, meaning little influence from specimen geometry on fracture toughness. Additionally, the ratio of KIcini/KIc was almost the same regardless of specimen geometry shape and α0 when 0.2 ≤ α0 ≤ 0.8.

An investigation into the role of specimen geometry when undertaking tribological testing on seal fin components

Labyrinth seal systems are used in aeroengines to seal the clearance, the understanding of the wear mechanism of labyrinth seal system is necessary to achieve better sealing performance. In this work a series of tests are conducted on a high-speed test rig capable of fin tip speeds of 100 m/s. With force and temperature measurements recorded in each case, the influence of specimen geometry is investigated. Surface examination and debris analysis is also performed using microscopy post-test. The wear mechanism was found to be influenced by fin geometry. A discrete fin was observed to trigger a more efficient material removal mechanism at both incursion conditions. Where the fin segment and ring-shaped fin leading to increased temperatures and material smearing. The heat dissipate role of fin was also observed during test where longer contact time of fin and abradable gives better heat removal performance.

Influence of specimen geometry and strain rate on elongation in tensile testing of packaging steel

Packaging steel is characterized by low thickness (0.1 mm – 0.5 mm) and ferritic microstructure resulting from low carbon contents. In combination with continuous annealing processes and temper rolling, this results in only little elongation observed in tensile tests. However, as in real forming processes much higher deformation occurs, it is important to receive true stress-true strain data up to a highest possible level e.g. to characterize material for finite element analysis. Therefore, tensile tests with three different measuring lengths (80 mm, 50 mm, 20 mm) were conducted for the packaging steel TH415. Likewise, the testing speed was reduced to investigate the possibility to receive more elongation under the condition of a constant stress level. The results revealed a significant increase in elongation when using smaller tensile test geometries. As well, the reduction in testing speed leads to much higher elongation while showing only little strain rate influence. While for the 80 mm geometry and standard speed no homogenous forming condition could be reached due to early failure before Lüders strain, this could be improved by using smaller testing specimens and a lower strain rate. Combining the influence of strain rate and geometry a significant increase of more than ten percentage points in elongation was reached.

Influence of specimen geometry on mode I fracture toughness of asphalt concrete

Determination of fracture toughness (KIc) for the asphalt mixture concrete requires employment of suitable testing methods and specimens. Disc-shape specimens are among the favorite test geometries for conducting the fracture toughness experiments on asphalt concrete materials since they can be manufactured easily from those samples obtained by the gyratory compactor machine. Semi-circular bend (SCB) and edge notch disc bend (ENDB) specimens are two suitable and well-known specimens in this regard, and both of them are tested using three-point bend setup. In order to compare the consistency of fracture toughness results obtained from these two specimens, an experimental study is performed herein on a typical asphalt concrete mixture. In the experiments, the thickness of SCB and ENDB specimens and also the loading rate and test temperature are considered as variable. It is found that the KIc values obtained from both SCB and ENDB testing methods are in good agreement. The corresponding value of KIc obtained from the SCB specimen being slightly smaller than the data obtained from the ENDB specimen. Using a two term KI + T strain-based fracture model, that the critical normal strain value for both specimens is shown to be nearly the same and constant for both SCB and ENDB specimens. In addition, it is found that the fracture toughness value and load carrying capacity of asphalt mixture increases by increasing the specimen thickness (from 30 to 70 mm) and the loading rate (from 1 to 6 mm/min), and by decreasing the test temperature (from −15 °C to −25 °C).

The Influence of Specimen Geometry and Strain Rate on the Portevin-Le Chatelier Effect and Fracture in an Austenitic FeMnC TWIP Steel

We studied the Portevin-Le Chatelier effect and fracture behavior of a FeMnC TWIP steel using high speed digital image correlation by varying the specimen geometry (flat vs. round) and test strain rate (0.001 vs. 0.1 s−1). The results show that the mean flow stress, the mean strain hardening rate and the mean strain rate sensitivity parameters are all independent of the specimen geometry and are uncorrelated with the presence or not of Portevin-Le Chatelier (PLC) bands, the type of PLC bands observed or the critical strain for band formation. However, both the fracture strains and stresses and the PLC behavior are highly geometry and/or strain rate dependent. Dynamic strain aging (DSA) and in particular the presence of PLC instabilities appears to play an important but as yet unclear role in promoting premature necking and final fracture.

Influence of Specimen Geometry on the Response of Post-Installed Anchors Subjected to Constant Load under Crack Opening and Crack Cycles

Abstract It is generally acknowledged that one of the most critical tests to capture the behavior of a post-installed fastener under seismic action is the so-called “seismic crack movement test,” which consists in applying a constant load to a single fastener installed in a crack subjected to opening and full closing cycles. This article presents experimental results of crack movement tests on large size post-installed anchors that show a strong influence of the geometry of the concrete specimen in which the anchor is installed. To improve the regularity of the crack plane, a feedback control using the crack opening signal is applied to the servo-hydraulic actuators. Results of seismic crack movement tests using two different test setups were compared. The major aspects are as follows: (i) splitting force generated by the anchor affects the restoring of the zero crack opening when increasing the number of cycles, and (ii) increasing the size of concrete element limits the effects of bending induced in the concrete specimen. The issue of residual crack opening at the zero actuator’s load is observed experimentally and is further approached both analytically and numerically. The parameters that mostly affect the crack closure phase, i.e., steel ratio, transfer length, and de-bonding length, are finally discussed.

Influence of specimen geometry on apparent Poisson’s ratio evaluated under the compressive loading of quasi-isotropic CFRP laminate

The effects of specimen geometry on the Poisson’s ratio of a quasi-isotropic carbon-fiber-reinforced polymer laminate were examined using compression tests. In particular, the divergence of the apparent Poisson’s ratio from the theoretical value was experimentally determined for a decreasing specimen width/thickness ratio (b/t). The observed tendency was then confirmed by simulations using a finite element analysis (FEA). The FEA was performed using a 3D model of the specimens to investigate the strain and stress distribution. In the evaluation of the apparent Poisson’s ratio, the strain in the width direction was shown to vary under the condition of low b/t. The FEA results revealed that changes to the width strain were caused by cross-sectional deformation under compressive loading, resulting from differences in layer angles and stiffness between the outermost and inner layers.

Influence of Specimen Geometry on Apparent Poisson’s Ratio Evaluated under the Compressive Loading of Quasi-Isotropic CFRP Laminate

Influence of Specimen Geometry on Apparent Poisson’s Ratio Evaluated under the Compressive Loading of Quasi-Isotropic CFRP Laminate

Influence of specimen geometries and drying conditions on concrete cracking in restrained elliptical ring tests

Abstract The restrained shrinkage elliptical ring test has been established as an efficient method for assessing the cracking potential of concrete at early ages because an elliptical ring can provide a higher degree of restraint compared with a circular one. In this study, a series of circular and elliptical concrete rings restrained by steel rings with various thicknesses were tested under top & bottom surfaces drying or outer circumferential surface drying. By comparing concrete cracking age under different geometrical and drying conditions, the effects of ring geometry, restraining steel ring thickness and drying condition on the cracking process in concrete rings were revealed. Furthermore, numerical analyses were conducted to investigate the fracture mechanism for circular and elliptical rings by applying a fictitious temperature field to simulate the shrinkage effect of concrete. It is found that the increase of steel ring thickness can enhance the degree of restraint, therefore shorten the cracking age for both circular and elliptical rings. However, the improvement is more significant for circular rings. The fracture processes under the two drying conditions, i.e. top & bottom surfaces drying and outer circumferential surface drying are completely different: for drying from outer circumferential surface, the crack initiates at the outer surface and propagates towards the inner surface; for drying from top & bottom surfaces, the crack initiates partially along the height direction at the inner circumference of a concrete ring, and propagates along the radial direction, step by step, until the crack propagates throughout the whole ring wall. In both cases, the self-restraint caused by the non-uniform shrinkage of concrete and the external restraint from the inner steel ring contribute the driving effects for crack propagation. In general, compared with circular rings, the elliptical rings demonstrate the advantage of providing a higher degree of restraint. The elliptical ring test method can, therefore, supplement the traditional circular ring test method for assessing cracking tendency of concrete with higher cracking resistance.

Influence of Specimen Geometry on Creep Strength of Long-Term Used Mod.9Cr-1Mo Steel Welded Joint

Influence of Specimen Geometry on Creep Strength of Long-Term Used Mod.9Cr-1Mo Steel Welded Joint