Effect Of Specimen Size Research Articles

Experimental study on the size effect on the equation of state of concretes under shock loading

Adopting the classical theory of hydrocodes, the constitutive relations of concretes are separated into an equation of state (EoS) which describes the volumetric behavior of concrete material and a strength model which depicts the shear properties of concrete. The experiments on the EoS of concrete is always challenging due to the technical difficulties and equipment limitations, especially for the specimen size effect on the EoS. Although some researchers investigate the shock properties of concretes by fly-plate impact tests, the specimens used in their tests are usually in one size. In this paper, the fly-plate impact tests on concrete specimens with different sizes are performed to investigate the size effect on the shock properties of concrete materials. The mechanical background of the size effect on the shock properties are revealed, which is related to the lateral rarefaction effect and the deviatoric stress produced in the specimen. According to the tests results, the modified EoS considering the size effect on the shock properties of concrete are proposed, which the bulk modulus of concrete is unpredicted by up to 20% if size effects are not accounted for.

Specimen size effect on dynamic modulus measurement of Cold recycled and full depth reclamation mixtures

Dynamic modulus was measured using large-scale (LS) and small-scale (SS) specimens of four cold recycled (CR) and one full depth reclamation mixtures. The study found emulsified mixtures showed similar and repeatable dynamic modulus (E*) results with both specimen geometries (<15% difference) and foamed mixtures showed poor agreement between specimens (>24% difference), likely due to the differences in the mix matrices. The mechanistic-empirical pavement design analysis showed that E* differences in LS and SS of CR mixtures with foam resulted in error in asphalt concrete (AC) rutting predictions for sections with a thin surface layer (25 mm [1 in.]) and did not affect rutting predictions once the surface layer thickness was above 76 mm (3.0 in.). An empirical SS to LS shift factor method is presented.

Specimen size effect on the strength of nickel-boron alloys

Nickel-boron alloys are prepared by an electrodeposition method. The as-deposited nickel-boron alloy is then annealed at 250 °C and 400 °C for 4 h. Their mechanical strengths and specimen size effects on the strength are evaluated by micro-compression test using pillar-type micro-specimens fabricated by focused ion beam system. In all as-deposited and annealed specimens, a smaller-is-stronger specimen size effect is confirmed. The compressive strength of the nickel-boron alloys reaches a maximum of 5.79 GPa with the smallest specimen size in this work.

Very High Cycle Fatigue Data Acquisition Using High-Accuracy Ultrasonic Fatigue Testing Equipment

Abstract Fatigue testing at ultrasonic frequency is a powerful method for rapid generation of high and very high cycle fatigue data. High accuracy of cyclic loading is the basis for reproducible test results, which can be obtained with closed-loop control of vibration amplitude and resonance frequency. Self-heating of test specimens can be suppressed by intermittent (pulse-pause) loading. In the present work, the high-accuracy ultrasonic fatigue testing equipment developed at the University of Natural Resources and Life Science, Vienna (BOKU) is described, and systematic investigations are presented that demonstrate the effects of cycling frequency, specimen size, and intermittent loading. Data obtained with additively manufactured (AMed) austenitic stainless steel 316L at 19 kHz are compared with electromagnetic resonation test results measured at 90 Hz. No influence of cycling frequency on fatigue lifetimes and fatigue limit was found when specimens of comparable size were used for tests at 19 kHz and 90 Hz. In contrast, the use of as-built specimens with smaller testing volume resulted in an increase in cyclic strength, demonstrating a size effect on fatigue properties. Polishing the surfaces of AMed specimens increased the fatigue limit by a factor of two. Furthermore, ultrasonic fatigue tests with intermittent loading and four different pulse lengths as well as continuous cycling were performed. The tests were conducted with wrought aluminum alloy 7075-T651 and with specimens containing small artificial surface defects. Similar lifetimes were measured in all testing series. Moreover, the same fatigue limit is found for all pulse lengths and for continuous cycling. This demonstrates that pulsed loading is a most suitable method to avoid specimen heating at ultrasonic frequency and that there is no influence on measured fatigue properties if ultrasonic loading is appropriately controlled. Measurement artifacts could be identified and avoided by measuring and recording all load amplitudes during ultrasonic fatigue tests.

Influence of specimen profile size and thickness on the dynamic compressive behavior of rigid PVC foams

Split Hopkinson Pressure Bar (SHPB) apparatuses were extensively utilized in the dynamic testing of polymeric foams in previous studies; however, there are many technical limitations on the specimen size when utilizing SHPBs. Consequently, most research on the influence of specimen size on the mechanical response was limited to the quasi-static loading regime. The specimen size effect was reported to be negligible in the quasi-static regime. This observation was traditionally extrapolated to the dynamic regime; however, the hypothesis has not been thoroughly verified by experimental testing. The present study represents the most thorough investigation (to date) on the influence of specimen shape, cross-sectional area and thickness on the dynamic mechanical response of Polyvinyl Chloride (PVC) foams. A drop tower testing machine equipped with a massive 45.45 kg dropping entity and a novel sacrificial energy dissipation system was employed for the dynamic testing. The findings from this work revealed a significant sensitivity to the specimen profile on the dynamic mechanical response of PVC foams in contrast to the negligible effects in the quasi-static regime. Investigating the effect of specimen thickness on the mechanical response further demonstrated that the engineering strain rate is not a suitable index for reporting PVC foams’ rate sensitivity. Instead, the impact velocity is more appropriate since specimens with different thicknesses exhibited a similar compressive stress/strain response when tested at the same impact velocities while experiencing different engineering strain rates. The influence of specimen shape (rectangular versus cylindrical) was negligible in both the quasi-static and dynamic regimes.

Measurements and estimation of frequency-dependent multi-scale viscoelastic damping properties of materials

The state-of-art viscoelastic property measurement and estimation methods at different frequencies/length scales inherently couple structural effects or sometimes lose accuracy for relevant parameters at smaller length scales in the material. We report a unified approach to measuring and estimating the frequency-dependent viscoelastic damping properties across different frequency scales independently of the specimen size effect and boundary conditions. The Dynamic Mechanical Analysis (DMA) method with three-point bending configuration is extended to higher-fidelity modeling in terms of time–frequency scales and material micro-mechanical scales together. The methodology demonstrates ways to identify the possible sources of undesired dynamics in the measurement process and eliminate those effects. It includes exciter tip contact dynamics in three-point bending configuration, anharmonic energy transfer to different frequencies (fractal bifurcation), and unmodelled artifacts or noise. Critically reviewing the standard DMA procedure with normal mode synthesis, this paper proposes a time–frequency Fourier spectral method that resolves a broader frequency range that extends to even acoustic/ultrasonic wave regimes of viscoelastic damping. An algorithm proposed in this paper with the advanced viscoelastic model with multi-parameters (standard linear solid model) estimates the fundamental material parameters at small length scales, which is more insightful to obtain a frequency-dependent correlation of material response to general dynamic loading. Stiffness and damping properties are estimated from measured data and validated for self-consistencies via different controls regarding static preload, specimen resonance, filtered noise, and model fidelity across the frequency range, and certain consistency and convergence properties of a series solution. The unified approach with a single test will be helpful in the design and evaluation of a wide variety of materials and their applications in vibration and acoustic problems. The proposed technique further demonstrates a novel way to extend low-frequency measurement to high-frequency response modeling.

Study on the Influence of Specimen Size and Aggregate Size on the Compressive Strength of Rock-Filled Concrete

Rock-filled concrete (RFC) technology is a new type of mass concrete construction technology, which consists of two basic components: the force transfer frame formed by large-size rock accumulation and the matrix formed by self-compacting concrete (SCC) filling. Its unique construction method also distinguishes RFC from ordinary concrete in terms of its force characteristics. In this paper, RFC is considered as a composite material consisting of aggregate and SCC; based on the realistic failure process analysis (RFPA) method, the effects of specimen size and aggregate size on the compressive strength of RFC were studied. Firstly, RFC cube specimens were prepared and uniaxial compression tests were conducted. During the preparation process, in order to eliminate the influence of factors such as shape, spatial distribution state, and volume share of aggregates on the compressive strength, aggregates of different sizes were set as spheres and arranged in simple cubic stacking; then a numerical model of RFC with different specimen sizes and different aggregate sizes was established for uniaxial compression numerical simulation experiments to analyze the variation law and failure pattern of the RFC compressive strength. The results indicate that the compressive strength of RFC exhibits a significant size effect and follows a negative exponential function distribution law; with the same volume fraction of aggregate, the smaller the aggregate size, the higher the compressive strength of the RFC will be, and this increasing trend gradually levels off. Based on the findings of this study, it is recommended that the size effect and the reduction of aggregate size on dam strength be taken into account in the design of RFC dams.

A physically-based constitutive model for amorphous glassy polymers in large deformations

A physically-based constitutive model for predicting the mechanical response of amorphous glassy polymers at room temperature and low strain rates was established within the frame of thermodynamics and kinematics. In our previous work (Lan et al., 2022b), the concepts of permanent entanglement (PE) and dynamic entanglement (DE) were utilized to reproduce the complicated behavior of amorphous glassy polymers from quasi-static to dynamic loading at temperatures from below to near the glass transition temperature. PE formed by the coiling of macromolecular chains is relatively stable and contributes to the yield and unloading behavior. DE formed by the weak interaction between monomers of adjacent segments is unstable and contributes to the macroscopic yield peak and strain hardening. However, due to including many parameters, the model is not easy to apply in practice. In this work, by ignoring the influence of temperature, the previous model (Lan et al., 2022b) was simplified. Taking polycarbonate (PC) and polystyrene (PS) as examples, the simplified model focused on the macroscopic mechanical behavior under simple compression and cyclic simple compression, analyzed the effects of mesh and specimen size on the evolution of shear bands under plane strain compression, and compared the obvious differences in localized deformation of these two types of amorphous polymers under plane strain compression. In addition, the forging process of PC at room temperature was simulated. By comparing the predictions with the experiments, it is demonstrated that the simplified model can reproduce the macroscopic mechanical response of amorphous polymers under simple compression, cyclic simple compression, plane strain compression and forging.

Comparative study on the dynamic compressive, tensile and flexural properties of soda-lime silicate glass

The mechanical behavior of brittle solids are influenced by many factors such as specimen sizes, surface conditions and loading conditions. This work focused on the mechanical properties of a soda-lime silicate glass under three kinds of loading, i.e. compression, tension and flexure. In addition, quasi-static, dynamic uniaxial-unidirectional (UU) and uniaxial-bidirectional (UB) tests were performed. Electromagnetic split Hopkinson pressure bar (ESHPB), a newly developed system, was adopted in the dynamic tests. A high-speed camera was employed to capture the dynamic failure process. Effects of loading rates, specimen sizes, stress waves and loading modes on the mechanical behavior of this glass were comparatively investigated. Testing results illustrated that specimen size and strain rate had significant influence on the strengths. Different from the tensile and flexural strengths, the compressive strength was sensitive to the loading stress waves. The flexural strength was generally higher than the tensile one and they could be mutually converted through the non-local failure theory. Fracture surface of glass fragment after tensile loading was observed by a scanning electron microscope (SEM) to reveal the microscopic features.

A microscale constitutive model for thin stainless steel sheets considering size effect

This research is focused on the modeling of the deformation behavior of thin austenitic stainless steel sheets to consider size effect in microscale. First, the material with two different thicknesses is heat treated to obtain different grain sizes, and then they are characterized by the uniaxial tensile tests. The experimental results show that flow stress decreases with the reduction of the sheet thickness and the increase of the grain size. The decline of the flow stress curve is associated with the decrease of the strength coefficient and increase of the hardening exponent as the plastic deformation is scaled down to the microscale. To better model the behavior of the material in the microscale, a new constitutive model is proposed based on the Swift equation to take into account the geometry and grain size effect. This model is also defined in the finite element model of the uniaxial tensile test. It is found that the flow stress curve predicted by the proposed constitutive model shifts down by the decrease of the number of grains across the thickness, which are consistent with the experimental results. In addition, the finite element model with the proposed constitutive model predicts accurately the deformation load in the uniaxial tensile tests. It can be concluded that the proposed constitutive model can provide a good description of the flow stress by considering the interactive effect of specimen and grain sizes and can be used in the modeling of material behavior in microforming processes.

The Effect of Specimen Size on Acoustic Emission Parameters and Approximate Position of Defects Obtained during Destructive Testing of Cementitious and Alkali-Activated Degraded Fine-Grained Materials.

Two sizes of test samples were selected to investigate the effect of size on the level of degradation. The smaller test specimens had dimensions of 40 × 40 × 160 mm, and the larger ones had dimensions of 100 × 100 × 400 mm. Both sizes of test specimens were always made of the same mortar. In one case, Blast Furnace Cement was chosen as the binder. In the other case, it was an alkali-activated material as a possibly more environmentally economical substitute. Both types of material were deposited in three degrading solutions: magnesium sulphate, ammonium nitrate and acetic acid. The reference set was stored in a water bath. After six months in the degradation solutions, a static elastic modulus was determined for the specimens during this test, and the acoustic emission was measured. Acoustic emission parameters were evaluated: the number of hits, the amplitude magnitude and a slope from the amplitude magnitude versus time (this slope should correspond to the Kaiser effect). For most of the parameters studied, the size effect was more evident for the more degraded specimens, i.e., those placed in aggressive solutions. The approximate location of emerging defects was also determined using linear localisation for smaller specimens where the degradation effect was more significant. In more aggressive environments (acetic acid, ammonium nitrate), the higher resistance of materials based on alkaline-activated slag was more evident, even in the case of larger test bodies. The experiments show that the acoustic emission results agree with the results of the static modulus of elasticity.

Specimen Size Effect on the Tensile Properties of Rolled Steel of Long-Term-Operated Portal Crane.

This paper presents the research results on the mechanical behavior of the low-carbon rolled steel of a sea portal crane after a 33-year operation depending on the operational stresses and rolling direction in order to assess its serviceability. The tensile properties of steels were investigated using rectangular cross-section specimens with different thicknesses and the same width. Strength indicators were slightly dependent on the considered factors (operational conditions, the cutting direction, and thickness of specimens). However, a clear trend of higher ultimate strength for thinner specimens was noticed, especially in the case of more brittle material due to its operational degradation. Plasticity of the tested steel specimens was more sensitive to the influence of the above-mentioned factors than strength but less sensitive than impact toughness. Uniform elongation was slightly less for thinner specimens regardless of the investigated steel state or the orientation of specimens relative to the rolling direction. The post-necking elongation was lower for transversal specimens compared with longitudinal ones, and the effect was more significant when testing steel with the lowest brittle fracture resistance. Among the tensile properties, non-uniform elongation was demonstrated to be the most effective for assessing the operational changes in the state of rolled steels.

Pullout performance of headed anchor studs in Engineered Cementitious Composites (ECC) with Polyvinyl Alcohol fibers

To study the pull-out resistance of headed anchor studs in Engineered Cementitious Composites (ECC) for steel-ECC composite structures, pull-out tests were carried out on 9 scenarios of ECC specimens. The failure modes, load–displacement curves, peak load (Nu), initial stiffness (K0.3), and ultimate displacement (Du) of studs in Polyvinyl Alcohol fiber (PVA)-ECC under different stud sizes (d = 13 mm and 16 mm), stud embedment depths (hef = 40 mm, 60 mm, and 80 mm) and fiber content (Vf = 2.0% and 2.5%) were obtained. Failure modes include (ductile) concrete cone failure, cone-splitting combined failure, and steel failure. For the specimens with concrete cone, either increasing d or hef increases K0.3, Nu, and Du, and Nu shows the greatest improvement. Increasing fiber content (Vf) exerts a significant enhancing effect on Nu, but exerts little effect on K0.3 and Du. Through the comparisons to the pull-out resistance of studs in high-strength concrete (HSC), the studs in ECC show evident advantages in ductility, toughness, and Nu. Based on the experimental results, the applicability of the original CCD model and two modified CCD models from literature to studs in ECC is discussed. The modified CCD model including the effect of stud size and specimen size presents the best accuracy in predicting Nu of studs in ECC. Overall, ECC is a promising material for steel–concrete composite structures, considering it evidently improves the pull-out performance of studs, thus the anchorage between steel and ECC.

Effects of Strain Rate and Specimen Size on the Behavior of Fine-Grained Soils

Effects of Strain Rate and Specimen Size on the Behavior of Fine-Grained Soils

Analytical and inverse method for determining high temperature properties of materials using small punch creep: a review

PurposeThis paper presents a review concerning the analytical and inverse methods of small punch creep test (SPCT) in order to evaluate the mechanical property of component material at elevated temperature.Design/methodology/approachIn this work, the effects of temperature, specimen size and shape on material properties are mainly discussed using the finite element (FE) method. The analytical approaches including membrane stretching, empirical or semi-empirical solutions that are currently used for data interpretation have been presented.FindingsThe state-of-the-art research progress on the inverse method, such as non-linear optimization program and neutral network, is critically reviewed. The capabilities of the inverse technique, the uniqueness of the solution and future development are discussed.Originality/valueThe state-of-the-art research progress on the inverse method such as non-linear optimization program and neutral network is critically reviewed. The capabilities of the inverse technique, the uniqueness of the solution and future development are discussed.

Fabrication, design, and optimization of hierarchical composite Kagome honeycomb sandwich structure under uniaxial compression

Abstract In this study, a hierarchical composite Kagome honeycomb sandwich (HCKHS) structure was manufactured based on the interlocking method, and its uniaxial compression performance was explored. Through experiments, the compressive strength, stiffness, energy absorption, and failure process of HCKHS specimens of seven different sizes were determined and compared. Mechanical analytical models were established, and the variation trend in the specific strength was predicted and compared with those of other advanced sandwich structures. The size effect of the HCKHS specimens was analyzed. The influence of a single variable on the core modulus, failure strength, and failure modes was discussed, and failure mechanism maps were drawn. The structure was optimized based on the maximum specific strength and engineering application, and the optimal size design ratio was obtained. The results showed that the HCKHS specimens exhibited excellent compressive properties with a convenient manufacturing process, making them suitable for lightweight applications in engineering. The optimization ideas presented herein are also applicable to other two-dimensional hierarchical or normal composite honeycomb sandwich structures with diamond, triangular, and hexagonal shapes.

Influence of fatigue precracking and specimen size on Master Curve fracture toughness measurements of EUROFER97 and F82H steels

EUROFER97 and F82H steels are two leading reduced-activation ferritic-martensitic (RAFM) steels for fusion first wall and blanket applications. Exposure to the harsh environment of fusion reactors can result in severe degradation of fracture toughness. Thus, the post-irradiation evaluation of fracture toughness is critical for understanding the material behavior. Due to the space constraints of irradiation facilities and challenges in controlling a uniform irradiation condition for large size specimens, the development of small specimen test techniques (SSTT) is indispensable to evaluate the performance of irradiated materials. In this study, we evaluated specimen size effects on the Master Curve fracture toughness of EUROFER97 and F82H steels. A wide variety of specimens, including 0.5 T compact tension (C(T)) specimens, 0.16 T mini-compact tension (miniC(T)) specimens, and 1.65 mm miniature bend bar specimens, were tested. The testing methodology was based on the Master Curve method in the ASTM E1921 standard. No specimen size effect was observed in 0.5 T C(T) and 0.16 T miniC(T) specimens on the Master Curve reference temperature T0, while 1.65 mm miniature bend bar specimens yielded a higher T0Q. A strong effect of fatigue precracking on T0 for 0.5 T C(T) and 0.16 T miniC(T) specimens was observed, such that testing on specimens with skewed fatigue precrack fronts resulted in lower T0 than for specimens with ASTM standard qualified straight fatigue precrack fronts. The results highlight the importance of experimental quality control in developing SSTT for Master Curve fracture toughness testing. Lastly, we also evaluated and provided recommendations on the minimum number of specimens needed for each specimen type for yielding reliable T0Q values.

Dowel–bearing behavior of bamboo scrimber for bolted–type joint

Dowel-bearing behavior is one of the key material characteristics in the design of laterally loaded joints with dowel-type fasteners and provides its strength and stability of structures. In this study, the dowel-bearing behavior of bolted joints on bamboo scrimber were investigated by analyzing the effect of specimen size, bolt diameter and loading direction on the dowel-bearing behavior. The estimation formulas of dowel-bearing strengths of bamboo scrimber for engineering utilization were developed based on conducting on 16-group experiments comprising a total of 80 half-hole samples. The results indicate that the initial stiffness was affected by the bolt diameter, sample thickness and loading direction. Dowel-bearing strength was only affected by bolt diameter and it decreased gradually with the increase in bolt diameter, irrespective of specimen sizes and loading direction. The failure mechanisms of the samples loaded in parallel- and perpendicular-to-grain were completely different. The existing empirical expressions was suitable for bamboo scrimber loaded in parallel-to-grain when larger bolts were used, but can under-estimate the dowel-bearing strengths in perpendicular-to-grain direction. Finally, semi-empirical regression-based formulas as functions of compressive strength and bolt diameter were proposed, which exhibited good agreement with the experimental dowel-bearing strength. The findings will be useful for designing safe and efficient bolted joints to promote more widespread use of bamboo scrimber in construction, as well as supplying basic data for systematic development of test and design standards for bamboo structures.

Experiment and meso-scale modelling on combined effects of strain rate and specimen size on uniaxial-compressive failures of concrete

This paper presents experimental and meso-scale modelling studies on the combined effects of strain-rate and specimen size on uniaxial compressive failure behaviour of concrete. A series of uniaxial compressive tests and meso-scale simulations were conducted on concrete with various specimen sizes under different strain-rates covering the strain-rate range of seismic load, with special focus on the quantitative contribution of end-friction to compressive strength and its corresponding strain-rate effect as well as size effect. Results indicate that the uniaxial compressive failure with end-friction follows an hourglass failure pattern while that without end-friction exhibits a columnar failure pattern. The end-friction effect can form different confined zone distributions for various sized specimens, which can cause the contribution of end-friction to compressive strength is size dependent as well as enhance the influence of specimen size on static and dynamic strength. The contribution proportion of end-friction to compressive strength is around 20∼25%. Moreover, larger-sized specimen performs a stronger strain-rate effect and the increasing strain-rate can weaken the influence of specimen size on the real compressive strength. The proposed real DIF empirical formula considering the size-dependency (covering the low strain-rate range) can well estimate the strain-rate effect for concrete with different sizes, which can provide a valuable reference for the numerical calculation of dynamic mechanical response and the safety design of concrete structures.

Experimental Model for Study of Thickness Effect on Flexural Fatigue Life of Macro-Synthetic-Fiber-Reinforced Concretes

As one of the most widely used building materials, concrete has a dominantly brittle or quasi-brittle behavior. Adding fibers to concrete affects its ductility behavior as well as some mechanical properties. Finding the relationship between the addition of fibers and the change in thickness of laboratory test samples made of concrete can help in designing the optimal thickness of real concrete layers (especially concrete pavements) to withstand dynamic loads. The purpose of this research is to provide an experimental model for investigating the effect of concrete specimen size, or the thickness effect of concrete sample, on the fatigue life of concrete. Accordingly, several concrete beams with three thicknesses (80, 100 and 150 mm), constant width, and two lengths (120 mm and 450 mm) were manufactured with fiber percentages of 0 and 4% by fraction volume. The employed fiber was twisted macro synthetic fiber. After curing for 28 days, the samples were subjected to fatigue loading at three stress levels until the onset of failure and cracking stage. Here, the experimental model of the relationship between the number of loading cycles, the stress level and the thickness of the sample is presented. The results show that increasing the specimen thickness and fiber content can enhance the fatigue life of concrete up to 68%.