Experimental crushing behavior and energy absorption of angular gradient honeycomb structures under quasi-static and dynamic compression

The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.

Determination of Material Parameters of EVA Foam under Uniaxial Compressive Testing Using Hyperelastic Models

The objective of this research was to determine the mechanical parameter from EVA foam and also investigate its behavior by using Blatz-Ko,Neo-Hookean,Mooney model and experimental test.The physical characteristic of EVA foam was also evaluated by scanning electron microscopy(SEM).The results show that Blatz-Ko and Neo-Hookean model can fit the curve at 5%and 8%strain,respectively.The Mooney model can fit the curve at 50%strain.The modulus of rigidity evaluated from Mooney model is 0.0814±0.0027 MPa.The structure of EVA foam from SEM image shows that EVA structure is a closed cell with homogeneous porous structure.From the result,it is found that Mooney model can adjust the data better than other models.This model can be applied for mechanical response prediction of EVA foam and also for reference value in engineering application.

Seismic performance of double- skin steel- concrete composite box piers: Part Ⅰ——Bidirectional quasi-static testing

To study the seismic performance of double-skin steelconcrete composite box（ DSCB） piers, a total of 11 DSCB pier specimens were tested under bidirectional cyclic loading. The effects of the loading pattern, the steel plate thickness, the axial load ratio, the slenderness ratio and the aspect ratio were taken into consideration. The damage evolution process and failure modes of the tested specimens are presented in detail. Test results are also discussed in terms of the hysteretic curve, skeleton curve, ductility and energy dissipation capacity of DSCB pier specimens. It can be concluded that the hysteretic performance of DSCB piers in one direction is affected and weakened by the cyclic loading in the other direction. DSCB piers under bidirectional cyclic loading exhibit good performance in terms of load carrying capacity, ductility, and energy dissipation capacity. Overall, DSCB piers can meet the basic aseismic requirements. The research results can be taken as a reference for using DSCB piers as high piers in bridges in strong earthquakeprone areas.

Evaluation of empirical estimation of uniaxial compressive strength of rock using measurements from index and physical tests

The uniaxial compressive strength(UCS) of rock is an important parameter required for design and analysis of rock structures,and rock mass classification.Uniaxial compression test is the direct method to obtain the UCS values.However,these tests are generally tedious,time-consuming,expensive,and sometimes impossible to perform due to difficult rock conditions.Therefore,several empirical equations have been developed to estimate the UCS from results of index and physical tests of rock.Nevertheless,numerous empirical models available in the literature often make it difficult for mining engineers to decide which empirical equation provides the most reliable estimate of UCS.This study evaluates estimation of UCS of rocks from several empirical equations.The study uses data of point load strength(Is(50)),Schmidt rebound hardness(SRH),block punch index(BPI),effective porosity(n) and density(ρ)as inputs to empirically estimate the UCS.The estimated UCS values from empirical equations are compared with experimentally obtained or measured UCS values,using statistical analyses.It shows that the reliability of UCS estimated from empirical equations depends on the quality of data used to develop the equations,type of input data used in the equations,and the quality of input data from index or physical tests.The results show that the point load strength(Is(50)) is the most reliable index for estimating UCS among the five types of tests evaluated.Because of type-specific nature of rock,restricting the use of empirical equations to the similar rock types for which they are developed is one of the measures to ensure satisfactory prediction performance of empirical equations.

Seismic performance evaluation of an infilled rocking wall frame structure through quasi-static cyclic testing

Earthquake investigations have illustrated that even code-compliant reinforced concrete frames may suffer from soft-story mechanism.This damage mode results in poor ductility and limited energy dissipation.Continuous components offer alternatives that may avoid such failures.A novel infilled rocking wall frame system is proposed that takes advantage of continuous component and rocking characteristics.Previous studies have investigated similar systems that combine a reinforced concrete frame and a wall with rocking behavior used.However,a large-scale experimental study of a reinforced concrete frame combined with a rocking wall has not been reported.In this study,a seismic performance evaluation of the newly proposed infilled rocking wall frame structure was conducted through quasi-static cyclic testing.Critical joints were designed and verified.Numerical models were established and calibrated to estimate frame shear forces.The results evaluation demonstrate that an infilled rocking wall frame can effectively avoid soft-story mechanisms.Capacity and initial stiffness are greatly improved and self-centering behavior is achieved with the help of the infilled rocking wall.Drift distribution becomes more uniform with height.Concrete cracks and damage occurs in desired areas.The infilled rocking wall frame offers a promising approach to achieving seismic resilience.

Effect of SACMA and QMW Test Methods on Compressive Properties of Composite Laminates after Low Velocity Impact

Experimental studies on the compressive behavior of composite laminates after low velocity impact was carried out with two test methods.One is SACMA Standard,and the other is a small dimensional specimen test method.Impact damage distributions,compressive failure process after impact,quasi static indentation and compression of laminates with a hole were brought into comparison between these two test methods.The results showed that there is a great difference between these two test methods.Compressive behavior of laminates after impact varies with different test methods.Residual compressive strength of laminates after low velocity impact measured with SACMA Standard can reflect stiffness properties of composite resins more wholely than that measured with the other method can do.Small dimensional specimen test method should be improved on as an experimental standard of compressive strength after impact.

Theoretical analysis on quasi-static lateral compression of elliptical tube between two rigid plates

Based on the rigid plastic theory; the load-deflection functions with and without considering the effect of strain hardening are respectively derived for an elliptical tube under quasi-static compression by two parallel rigid plates. The non-dimensional load-deflection responses predicted by the present theory and the finite element simula- tions are compared, and the favorable agreement is found. The results show that strain hardening may have a noticeable influence on the load-deflection curves of an elliptical tube under quasi-static compression. Compared with the circular counterpart, the ellip- tical tube exhibits different energy absorption behavior due to the difference between the major axis and the minor axis. When loaded along the major axis of a slightly oval tube, a relative even and long plateau region of the load-deflection curve is achieved, which is especially desirable for the design of energy absorbers.

Compressive Strength Prediction of Porous Concrete Using Nondestructive Tests

This research focused on a prediction of compressive strength in porous concrete based on the ratio of air-entrained agents in the concrete slab using nondestructive testing methods such as the Impact Echo （IE） method, Spectral Analysis of Surface Wave （SASW） method and Free-Free Resonance （FFR） test. The method that best predicts the strength of the concrete slab can be derived from a relationship between compressive strengths and stress wave velocities. Concrete slab specimens of varying air content, were formed with a mix ratio of air-entrained agent of 0%, 0.15%, 0.3%, 0.7% and 1.5% by weight. These slabs were tested and analyzed to measure the stress wave velocities in order to develop a correlation with compressive strengths. The plot between the stress waves and compressive strengths showed a stiffslope up to an air ratio of 4% with a less steep slope beyond this point. In the process of predicting the compressive strength of concrete slab specimens, the prediction of compressive strength based on the compression wave velocity caused an average error of 4.9% in the compression wave velocity, and the prediction of compressive strength based on the surface wave velocity caused an average error of 2.2% in the surface wave velocity.

ADVANCED FREQUENCY-DIRECTED RUN-LENTH BASED CODING SCHEME ON TEST DATA COMPRESSION FOR SYSTEM-ON-CHIP

Test data compression and test resource partitioning （TRP） are essential to reduce the amount of test data in system-on-chip testing. A novel variable-to-variable-length compression codes is designed as advanced fre- quency-directed run-length （AFDR） codes. Different [rom frequency-directed run-length （FDR） codes, AFDR encodes both 0- and 1-runs and uses the same codes to the equal length runs. It also modifies the codes for 00 and 11 to improve the compression performance. Experimental results for ISCAS 89 benchmark circuits show that AFDR codes achieve higher compression ratio than FDR and other compression codes.

An Efficient Test Data Compression Technique Based on Codes

This paper presents a new test data compression/decompression method for SoC testing,called hybrid run length codes. The method makes a full analysis of the factors which influence test parameters：compression ratio,test application time, and area overhead. To improve the compression ratio, the new method is based on variable-to-variable run length codes,and a novel algorithm is proposed to reorder the test vectors and fill the unspecified bits in the pre-processing step. With a novel on-chip decoder, low test application time and low area overhead are obtained by hybrid run length codes. Finally, an experimental comparison on ISCAS 89 benchmark circuits validates the proposed method

Constitutive relationship of IN690 superalloy by using uniaxial compression tests

The hot deformation behavior of IN690 superalloy was characterized in a temperature range of 1273-1473 K and a strain rate range of 0.01-10 s^-1 using uniaxial compression tests on process annealed material.The constitutive relations between flow stress and effective strain,effective strain rate as well as deformation temperature were studied.It can be concluded that the flow stress significantly reduces with the deformation temperature of IN690 superalloy increasing.Whereas,there is a significant increase of flow stress when the strain rate increases from 0.1 s^-1 to 10 s^-1.Based on the hyperbolic-sine Arrhenius-type equation,a constitutive equation considering compensation of strain was developed.The activation energy and the material constants（Q,n and ln A） decrease as the deformation strain increases.The strain dependent term is successfully incorporated in the constitutive equation through a quartic equation.A good agreement between the experimental data and the predicted results has been achieved,indicating that the proposed constitutive equation and the methods of determing the material constants are suitable to model the high temperature deformation behavior of IN690 superalloy.

Stress-strain behavior of plastic concrete using monotonic triaxial compression tests

The mechanical behavior of plastic concrete used in the cut-off walls of earth dams has been studied. Triaxial compression tests on the specimens in various ages and mix designs under different confining pressures have been done and the stress-strain behavior of such materials and their strength parameter changes have been experimentally investigated. It has been observed that increasing the confining pressures applied on the specimens causes the material behavior to be alike the more ductile materials and the compressive strength increases considerably as well. Moreover, a parametric study has been carded out to investigate the influence of essential parameters on the shear strength parameters of these materials. According to the research, increasing the coarse to fine aggregates ratio leads to the increase of compressive strength of the specimens as well as the increase of the cohesion and internal friction angle of the materials. Furthermore, the bentonite content decrease and the cement factor increase result in an increase of the cohesion parameter of plastic concretes and decrease of the internal friction angle of such materials.

An investigation into the effects of lime on compressive and shear strength characteristics of fiber-reinforced clays

To meet the ever-increasing construction demands around the world during recent years,reinforcement and stabilization methods have been widely used by geotechnical engineers to improve the performances and behavior of fine-grained soils.Although lime stabilization increases the compressive strength of soils,it reduces the soil ductility at the same time.Recent research shows that random fiber inclusion modifies the brittleness of soils.In the current research,the effects of lime and polypropylene(PP)fiber additions on such characteristics as compressive and shear strengths,failure strain,secant modulus of elasticity(E50)and shear strength parameters of mixtures were investigated.Kaolinite was treated with 1%,3% and 5% lime by dry weight of soil and reinforced with 0.1% monovalent PP fibers with the length of 6 mm.Samples were prepared at optimum conditions and cured at 35℃ for 1 d,7 d and 28 d at 90% relative humidity and subsequently subjected to uniaxial and triaxial compression tests(UCT and TCT)under cell pressures of 25 kPa,50 kPa and 100 kPa.Results showed that inclusion of random PP fibers to clay-lime mixtures increases both compressive and shear strengths as well as the ductility.Lime content and curing period were found to be the most influential factors.Scanning electron microscopy(SEM)analysis showed that lime addition and the formation of cementitious compounds bind soil particles and increase soil/fiber interactions at interface,leading to enhanced shear strength.The more ductile the stabilized and reinforced composition,the less the cracks in roads and waste landfill covers.

Temperature Effect on the Mechanical Behavior of Acrylic Polymers under Quasi-static and Dynamic Loading

In this paper, the mechanical behavior of acrylic polymers at elevated temperature was investigated. Four acrylic polymers were tested at high strain rate by using compression Hopkinson bar and at quasi-static strain rate by using an Instron servo hydraulic axial testing machine with the testing temperature from 218K to 393K. The results show that the mechanical property of acrylic polymers depends heavily on the testing temperature. The yield stress and Young's modulus were found to decrease with increasing temperature at low strain rate. At very low temperature, the materials display typical brittle fracture; however their plasticity improves remarkably at high temperatures. The predictions of the mechanical behavior including the effect of temperature and strain rate using a proposed theoretical model have a good agreement with experimental results.

Experimental research on creep behaviors of sandstone under uniaxial compressive and tensile stresses

The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.

Seismic performance of precast bridge columns connected with grouted corrugated-metal duct through biaxial quasi-static experiment and modeling

In this paper,the seismic behaviors of precast bridge columns connected with grouted corrugated-metal duct(GCMD)were investigated through the biaxial quasi-static experiment and numerical simulation.With a geometric scale ratio of 1:5,five specimens were fabricated,including four precast bridge columns connected with GCMD and one cast-in-place(CIP)bridge column.A finite element analysis model was also established by using OpenSees and was then calibrated by using the experimental results for parameter analysis.The results show the biaxial seismic performance of the precast bridge columns connected with GCMD was similar to the CIP bridge columns regarding ultimate bearing capacity and hysteresis energy,and further,that it could meet the design goal of equivalent performance.The seismic performance of the precast bridge columns connected with GCMD deteriorated more significantly under bi-directional load than under uni-directional load.A proper slenderness ratio(e.g.,7.0-10.0)and longitudinal reinforcement ratio could significantly improve the energy dissipation capacity and deformation capacity of the precast bridge columns,while the axial load ratio and concrete strength had little influence on the above properties.The research results could bring insights to the development of the seismic design of precast bridge columns connected with GCMD.

Temperature-controlled triaxial compression/creep test device for thermodynamic properties of soft sedimentary rock and corresponding theoretical prediction

In deep geological disposal of high-level nuclear waste,one of the most important subjects is to estimate long-term stability and strength of host rock under high temperature conditions caused by radioactive decay of the waste.In this paper,some experimental researches on the thermo-mechanical characteristics of soft sedimentary rock have been presented.For this reason,a new temperature-controlled triaxial compression and creep test device,operated automatically by a computer-controlled system,whose control software has been developed by the authors,was developed to conduct the thermo-mechanical tests in different thermal loading paths,including an isothermal path.The new device is proved to be able to conduct typical thermo-mechanical element tests for soft rock.The test device and the related testing method were introduced in detail.Finally,some test results have been simulated with a thermo-elasto-viscoplastic model that was also developed by the authors.

DELAMINATION FORMATION AND DELAMINATION PROPAGATION OF COMPOSITE LAMINATES UNDER COMPRESSIVE FATIGUE LOADING

Fatigue tests of the smooth composite laminates and the notched composite laminates under compressive cyclic loading have been carried out. The damage mechanism is discussed and analyzed. Damage evolution is monitored using stiffness decay. From these tests, it is found that the initial delamination occurs at the free boundary of smooth specimens, or the notch boundary of notched specimens, subjected to the compression-compression cyclic load. A point of view in relation to two-phases of compression fatigue delamination of composites is proposed, namely, compression-compression delamination consists of the delamination formation phase and the delamination propagation, and there is a 'damage transition point' to separate this two-phases. Furthermore, an empirical modulus degradation formula and its parameters fitting method are presented. According to the test data handling results, it is shown that this formula is univocal and can fit the test data conveniently. In addition, two kinds of new anti-buckling devices are designed for these tests. At last, the E-N curves, the D-N curves and the S-N curve of the smooth carbon fiber reinforced composite laminates of T300/648C are determined to predict the fatigue life of the notched composite laminate. And the E-N curve of the notched specimens at the given load ratio R = 10 and minimum load Pmin = -0.45 kN is also measured to verify the estimated result of fatigue life.

Compressive deformation behavior of an indirect-extruded Mg-8Sn-1Al-1Zn alloy

The medium and warm deformation behaviors of an indirect-extruded Mg-8Sn-IAI-IZn alloy were investigated by compression tests at temperatures between 298 and 523 K and strain rates of 0.001-10 s-1. It was found that the twinning-slip transition temperature was strain rate dependent, and all the true stress-true strain curves could be divided into two groups： concave and convex curves. Associated microstructural investigations indicated that the dynamic recrystallization （DRX） be- havior of the alloy varied with deformation conditions. At high strain rate and low temperature, dynamically recrystallized grains preferentially nucleated and developed in the twinned regions, indicating that twinning-induced DRX was dominant. While, at low strain rate, DRX developed extensively at grain boundaries and twins, and the process of twinning contributed to both oriented nucleation and selective growth. For the studied alloy, cracks mainly initiated from the shear band and twinning lamellar over the ranges of temperature and strain rate currently applied.

Impact of Freeze-Thaw Cycles on Compressive Characteristics of Asphalt Mixture in Cold Regions

Low average temperature, large temperature difference and continual freeze-thaw （F-T） cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixtures＇ compressive characteristics. Exponential model was applied to analyze the variation of compressive characteristics with F-T cycles; Loss ratio model and Logistic model were used to present the deterioration trend with the increase of F-T cycles. ANOVA was applied to show the significant impact of F-T cycles and asphalt- aggregate ratio. The experiment results show that the compressive strength and resilient modulus decline with increasing F-T cycles; the degradation is sharp during the initial F-T cycles, after 8 F-T cycles it turns to gentle. ANOVA results show that F-T cycles, and asphalt-aggregate ratio have significant influence on the compressive characteristics. Exponential model, Loss ratio model and Logistic model are significantly fitting the test data from statistics view. These models well reflect the compressive characteristics of asphalt mixture degradation trend with increasing F-T cycles.