Compression Specimens Research Articles

Experimental characterization of compression failure mechanism initiation and growth in notched carbon fiber reinforced composite specimens

This paper describes an experimental investigation to evaluate the compression failure mechanisms of kink banding, splitting, and delaminations under non-standard quasi-static loading of laminated carbon fiber reinforced composites. Tests were performed on double-edge notch compression (DENC) specimens to observe microscopic compressive damage initiation and progression. Acoustic emission results from specimens loaded to failure were used to define ranges of static stress associated with different forms of damage. Subsequent tests were interrupted at these stress intervals and results obtained from multiple inspection techniques provide quantified characterization of failure mechanism initiation and growth as a function of applied load level. Optical images of the exterior surfaces, micrographs of the laminate thickness generated via a grind/polish procedure, and postmortem X-ray computed tomographs provide detailed information on the 3D morphology and evolution of failure mechanisms in the laminate. Key failure characteristics include interior kink bands, surface ply splitting, and delaminations at two different types of interfaces. Kink bands are only present near ultimate failure while splitting and delamination initiate at approximately 50% lower stress levels. The experimental observations provide insight into the critical and subcritical nature of these failure mechanisms and their possible interactions in a multidirectional laminate under compression loading.

Study on the deformation behavior of AZ31B-O magnesium alloy with the VPSC model

The mechanical anisotropy of the magnesium alloy AZ31B-O was investigated using the Viscoplastic-Self-Consistent (VPSC)-Twinning and Detwinning (TDT) model. The anisotropic behavior of the material under uniaxial strain was studied using five distinct sheet orientations. In order to investigate the mechanical behavior under uniaxial compression, four alternative specimen orientations were employed. The VPSC model with the TDT mechanism was used to simulate the uniaxial tension and compression experiments. For tensile strain, the magnesium alloy samples were mainly regulated by base slip and prismatic slip. In compression of magnesium alloy samples, it was dominated by basal slip and {10–12} twinning. In all compression specimens, the grain c-axes are parallel to the compression axis regardless of the initial orientation. The r-values under different uniaxial strain paths have been also predicted by using the VPSC-TDT model. The negative r-values under uniaxial compression along RD to TD were further explained. The contribution of {10–12} twinning to plastic strain and the extra hardening induced by {10–12} extension twinning were discussed in depth. This study confirms that the extra hardening induced by {10–12} extension twinning will perform an important function when the twin volume fraction reaches a degree of about 50% with the active pyramidal slip at the same time.

Microstructure Characteristics of Porous NiTi Shape Memory Alloy Synthesized by Powder Metallurgy during Compressive Deformation at Room Temperature

Porous NiTi shape memory alloys (SMAs) possess compatible mechanical properties with human bones and can effectively reduce the risk of stress shielding and stress concentration; therefore, they have been termed promising candidates for orthopedic implants. However, microstructure characteristics of porous NiTi SMAs during plastic deformation have rarely been investigated. The present study aims to specifically investigate microstructure characteristics and the corresponding underlying mechanisms of fabricated porous NiTi SMAs via a conventional sintering (CS) process with NaCl space holder during compressive deformation at room temperature. To realize the aforementioned target, X-ray diffraction (XRD), scanning electron microscope (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) are applied in the present study. The results show that the fabricated porous NiTi SMA is 51.8% for porosity, 181.65 μm for the average pore size, and 0.78 μm for the average grain size. Many Ni4Ti3 and NiTi2 phases are formed in the mixed matrix with dominant B2 (NiTi) and some B19′ (NiTi). Severe inhomogeneous deformation happens within compressed specimens, leading to the occurrence of tangled dislocation and shear bands. Microcracks occur within fabricated porous NiTi SMAs at a deformation degree of 9.2%; then, they extend quickly to form macrocracks, which finally results in the failure of regions between pores. The observed nanocrystallization and amorphization around microcrack tips within the 12.5%-deformed sample can be attributed to the relatively small grain size and the grain segmentation effect via statistically stored dislocation (SSD) and geometrically necessary dislocation (GND).

Improvement of Analytical Model for Oblique Cutting—Part I: Identification of Mechanical Characteristics of Machined Material

Analytical cutting models have recently become quite widespread due to the simplicity and rapidity of calculations as well as the stability of the solutions. This paper considers a procedure for determining the mechanical properties of machined material based on parameters for the analytical model of oblique cutting for a certain range of changes in cutting modes and inclination angles of the tool cutting edge. The model is based on the energy method of determining the main cutting process characteristics using the extreme assumptions of continuum mechanics. It is proposed to determine the parameters characterizing the mechanical properties of the processed material using the Johnson–Cook constitutive equation in two stages: preliminary determination of the constitutive equation parameters based on the results of mechanical compression specimen tests and experimental data of the oblique cutting process, and specifying the generalized values of the constitutive equation parameters using the inverse method through the finite element cutting model. The adequacy of the applied analytical cutting model is confirmed by comparing the kinetic characteristic values calculated using the analytical model of oblique cutting with the application of the specified parameters of the constitutive equation and the measured values of the kinetic characteristics. The deviation between the calculated and measured values of the cutting force components when changing the cutting depth (undeformed chip thickness) does not exceed 15%. The difference between the calculated and measured values of the cutting force components when the cutting speed is changed is about 20%.

The fibre kinking fracture toughness of laminated composites under combined compression and shear

Compact compression specimens with off-axis fibres are employed in this paper, to investigate the effect of in-plane shear stress on the fibre kinking compressive fracture toughness of laminates. The strain distribution on the surface of the specimen was analysed using the digital image correlation method, and the damage process was monitored with thermal imaging. It was noted that the in-plane shear stress introduced by off-axis angle fibres caused an increase in the values of the R-curves when the off-axis angle was 10° or more. The microscopic morphology reveals that as the off-axis angle of the fibres increases, there is an increasing splitting of large fibre bundles, followed by the fibre compression failure within these bundles. This multi-step damage process may be responsible for the increase in energy dissipation.

A shear modified GTN model based on stress degradation method for predicting ductile fracture

The Gurson–Tvergaard–Needleman (GTN) model has provided a powerful description of the nucleation growth and coalescence of micro voids, but it has limitations in simulating shear fracture due to the absence of a description of shear localization behavior. A shear improvement method is proposed for simulating the ductile fracture of materials under different stress states. The modified model not only allows for strain hardening of the matrix material, but also accounts for the stress degradation caused by shear. The strength equation of the material is described by both the shear stress state function and a decay function, making it easier for materials under shear stress state to experience material softening and further inducing shear fracture. The modified GTN model is developed by incorporating the shear stress degradation factor into the yield function, while taking into account both void growth and shear failure mechanisms. By carefully calibrating the model’s parameters, the deformation and fracture processes of tensile, plane strain, notch tensile, and compression specimens in the 7A52 aluminum alloy are simulated. The damage evolution behavior of the material under different stress states is analyzed. The results indicate that the damage include void growth mechanism and void shear mechanism. The proportions of these two mechanisms vary under different levels of stress triaxiality. Upon localizing material deformation, the shear stress state intensifies, and the shear damage mechanism assumes a critical role in fracture. The modified GTN model accurately predicts the load-displacement response and fracture path of the 7A52 aluminum alloy under a wide range of stress states.

Making Shear Simple – Validation of the Shear Compression Specimen 0 (SCS0) for Shear Testing

Making Shear Simple – Validation of the Shear Compression Specimen 0 (SCS0) for Shear Testing

Research on axial compressive behavior of steel-fiber-reinforced recycled concrete-filled square steel tube slender columns

This paper presents an experimental and analytical study of the axial behavior of steel-fiber-reinforced concrete-filled square steel tube slender columns. A total of 25 axially compressive column specimens are manufactured to investigate the effects of the mass replacement percentage of recycled coarse aggregates (Rp), tube wall thickness (Ts), length-to-width ratio of columns (Lc), and steel fiber content (Vsf) on the performance of slender columns. The results show that the effects of Lc and Ts on the compressive behavior of the column specimens are significant owing to changes in the confinement effect and instability. In terms of the bearing capacity, the compressive strength increases by 12.45%–23.19% as Ts increases from 3 to 5 mm but decreases by 4.35%–10.65% as Lc increases from 6 to 12. However, the incorporation of steel fibers improves the post-peak load mechanical behavior of the slender columns by performing anchoring and bridging effects, and when Vsf reaches 1.2%, it tends to compensate for the reduction caused by changes in Lc and Ts. The synergistic action of the column specimens under axial compression is quantified based on an energy consumption indicator. In addition, predictions of the bearing capacity of the slender columns specified in the Eurocode 4, GB 50936-2014, and Han model are compared and discussed. An incremental iteration model is proposed, and the predicted values are similar to the experiment results with reasonable safety margins.

Experimental characterization of tensile and compressive translaminar fracture toughness coupling multi-physics measurements

The study of the failure modes of carbon fiber reinforced polymers is essential due to their extensive use in industry. Translaminar failure (at the scale of the laminate) has been studied extensively the main goal being to compute the critical strain energy release rate in mode I of the ply GIC_ply but large variations can be observed between papers. This study investigates this failure mode of a carbon/epoxy laminate, using Compact Tension (CT) and Compact Compression (CC) specimens. The stacking sequence used is [45/-45/(0/90)4]s where 45° plies on the outside efficiently prevented the buckling of the specimen to be observed, as well as plasticity of the matrix. Moreover, this layup is rather similar to real-life industrial stacking sequences. Strains fields and axes displacement were obtained using digital image correlation. Infrared images were used to follow the crack propagation during the loading of the specimen and compared to DIC and X-ray tomography crack length measurements. IR measurements studied from a qualitative point of view were thus shown to be an efficient and reliable method. GIC of the laminate GIC_lam was computed with both the ASTM-E399 and compliance methods, and finally GIC_ply was computed using a rule of mixtures. Secondary damage was detected and its effects on the energy dissipated were quantified using strain fields, X-ray and infrared images. This enabled a more accurate rule of mixtures to be redefined. The failure scenarios of all specimens were eventually exhibited. GIC_ply values in tension were found to be higher than in the literature whereas in compression it was found to be lower than in the literature, due to crack propagation being detected earlier by means of IR measurements.

An automatic thermo-mechanical testing apparatus for metal forming applications

Dynamic testing of materials is necessary to model high-speed forming processes (e.g. hammer forging, blanking, forming, etc.) and crash/impact behaviour of structures, amongst others. The most common machines to perform medium to high-speed tests are the servo-hydraulic high-speed tensile and compression machines and the Hopkinson bars. The paper analyses the use of a newly-developed laboratory testing facility, named the Automatic Thermo-Mechanical Tester (ATMT). This testing machine is equipped with a pneumatically accelerated Direct Impact Drop Hammer (DIDH), a furnace and automatised robotic arm, capable of characterising materials at intermediate strain rates, ranging from 100 to 300 s−1 in combination with temperatures up to 1350 °C. The hammer has been designed and constructed to conduct a variety of material characterisation tests, such as, upsetting or plane strain compression tests as well as component tests for validation purposes. The DIDH allows testing standard compression specimens at average strain rates in the order of 100 s−1 that decrease progressively until the it is fully stopped. It is, in combination with universal testing machines and Hopkinson bar systems, particularly suitable for experimental validation of loading-rate dependant material models. Compression tests were conducted with different hammer impact velocities generating a variety of strain rates at varying temperatures on S235JR structural steel, OFHC copper and wrought Inconel 625 nickel-based superalloy to assess the potential of the novel apparatus. A detailed finite element numerical study of the system was performed to assess several aspects such as the effect of the specimen geometry or its capability as an intermediate testing device, simulating a simplified system and the full Direct Impact Drop Hammer apparatus.

Pengaruh Bahan Tambah Serat Ijuk Terhadap Sifat Mekanik Beton SCC (Self Compacting Concrete)

In the current development of concrete innovation technology, there are also expensive materials that are cheap as concrete additives for the efficiency of the cost of making concrete. cheap and can be used as concrete innovation. The purpose of adding palm fiber fiber is to improve the quality of concrete, both compressive strength and split tensile strength. The method used in this study was experimentation by adding palm fiber to the SCC concrete mixture with variations of 2%, 4% and 6%. As for the addition of chemical substances, the superplasticizer admixture aims to make it easier for SCC concrete to achieve a slump flow value that meets the requirements. After testing, the highest compressive strength test specimen is BC 1 2% palm fiber worth 19.38 MPa and for the lowest compressive strength test is BC 2 6% palm fiber worth 5.46 MPa. And for the split tensile strength test the highest is BC 4 2% palm fiber worth 9.47 MPa and for the lowest split tensile strength test is BC 3 6% palm fiber worth 5.82 MPa.

A new method for ultrasonic fatigue component frequency modulation: From ultrasonic horn to uniaxial and multiaxial specimens

Ultrasonic fatigue specimens require rigorous design. The entire machine and specimen setup must vibrate in resonance at high frequencies, with the desired mode shapes that produce the intended stresses. The connection between parts must be considered too as they should allow for the desired mode shape to vibrate in free-free conditions. Most published research uses an analytical method that works only for uniaxial tension–compression or pure torsion specimens. This limits the range of experiments. In this paper, a semi-analytical formulation that can model more complex ultrasonic specimen geometries for a variety of stress states is proposed, namely multiaxial tension–torsion. Comparing numerical simulations with the analytical method show a good correlation between results. This work can help other researchers to design and conduct more varied and efficient ultrasonic fatigue experiments.

A novel theoretical model for obtaining Norton's law of creep materials using different small specimens

The test method for evaluating the creep properties of a material using small specimens mostly relies on an empirical correlation equation derived through uniaxial tests, and it is difficult to obtain a unified theoretical model for creep specimens with different configurations. We propose a novel and unified theoretical model that describes the creep displacement–time curves based on the energy density equivalent principle, which can be expressed as h = h*B(P/A*)vt. A simple expression of the model parameters related to sizes was established for cantilever beam, ring compression, and flat small punch specimens using finite element analysis (FEA). Forward and reverse verification using FEA and experimental validation of the model using small specimens of a zinc alloy (ZA27) at 27°C were conducted. The results revealed that the Norton's law parameters predicted using the new creep model are in good agreement with the results obtained using the uniaxial creep test. The new model does not require an empirical correlation between the displacement and uniaxial reference equivalent strain and has a uniform characterization for four types of specimens with different configurations and sizes.

Experimental and numerical investigation on the dynamic shear failure mechanism of sandstone using short beam compression specimen

In this study, a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression (SBC) specimen into the split Hopkinson pressure bar (SHPB) system. Firstly, the stress distribution of SBC specimen is comprehensively analyzed by finite element method (FEM), and the results show that the optimal notch separation ratio of SBC specimen is C/H = 0.2 to achieve successful dynamic simple-shear tests. Then, dynamic shear tests are conducted on sandstone using the SBC-SHPB method. Via careful pulse shaping technique, the dynamic force balance is guaranteed for SBC specimens, and the testing results show that the dynamic shear strength of sandstone is significantly rate-dependent. Combining the results of dynamic compression and tension tests, the failure envelopes of sandstone under different loading rates are obtained in the principle stress plane. It is found that the failure envelope of sandstone constantly expands outwards with increasing loading rate. Moreover, the energy partition of SBC specimen is quantified by virtue of high-speed digital image correlation (DIC) technique. The results show that the kinetic energy portion is non-negligible, and the shear fracture energy increases with increasing loading rate. In addition, the microscopic shear cracking mechanism of SBC specimen is analyzed by the thin section observation: the intra-granular (TG) fracture of minerals dominates the dynamic shear failure of sandstone, and the portion of TG fracture increases with increasing loading rate. This study provides a convenient and reliable method to measure the dynamic shear property and failure mechanism of rocks.

Ductile fracture behavior of in situ TiB2 particle reinforced 7075 aluminum matrix composite in various stress states

The fracture behavior of an in situ TiB2 particle reinforced 7075 aluminum matrix composite in various stress states was investigated by mechanical tests, microscopic characterization, and numerical simulations. Four sets of tensile specimens, one group of shear specimens, and one group of compression specimens were designed, and mechanical experiments were conducted on these six groups of specimens. The strain distributions of the six groups of specimens during deformation were investigated by in situ strain testing and finite element simulation. The fracture morphology of the specimens was characterized to analyze the damage mechanism in different stress states. It was found that the fracture mechanism of the material is mainly interfacial debonding and particle fracture, manifested as tensile fracture under high stress triaxiality and shear fracture under low stress triaxiality. For the tensile fracture, the nucleated voids grew with the maximum principal stress; for the shear fracture, they showed significant shape change with the maximum shear stress but little volume change. Based on the fracture mechanisms uncovered by the experiments, a modified ductile fracture criterion, considering the influence of both the maximum principal stress and maximum shear stress, was developed for the composite. Comparison with the modified Mohr–Coulomb, Lou–Yoon–Huh, Hu, and Mu models shows that the proposed model can predict the ductile fracture behavior of the aluminum matrix composites more accurately.

Finite Element Analysis of Dynamic Recrystallization Model and Microstructural Evolution for GCr15 Bearing Steel Warm-Hot Deformation Process.

Warm deformation is a plastic-forming process that differs from traditional cold and hot forming techniques. At the macro level, it can effectively reduce the problem of high deformation resistance in cold deformation and improve the surface decarburization issues during the hot deformation process. Microscopically, it has significant advantages in controlling product structure, refining grain size, and enhancing product mechanical properties. The Gleeble-1500D thermal-mechanical physical simulation system was used to conduct isothermal compression tests on GCr15 bearing steel. The tests were conducted at temperatures of 600-1050 °C and strain rates of 0.01-5 s-1. Based on the experimental data, the critical strain model and dynamic recrystallization model for the warm-hot forming of GCr15 bearing steel were established in this paper. The model accuracy is evaluated using statistical indicators such as the correlation coefficient (R). The dynamic recrystallization model exhibits high predictive accuracy, as indicated by an R-value of 0.986. The established dynamic recrystallization model for GCr15 bearing steel was integrated into the Forge® 3.2 numerical simulation software through secondary program development to simulate the compression process of GCr15 warm-hot forming. The dynamic recrystallization fraction was analyzed in various deformation regions. The grain size of the severe deformation zone, small deformation zone, and difficult deformation zone was compared based on simulated compression specimens under the conditions of 1050 °C and 0.1 s-1 with the corresponding grain size obtained with measurement based on metallographic photos; the relative error between the two is 5.75%. This verifies the accuracy of the established dynamic recrystallization and critical strain models for warm-hot deformation of GCr15 bearing steel. These models provide a theoretical basis for the finite element method analysis and microstructure control of the warm-hot forming process in bearing races.

HUBUNGAN KUAT TEKAN DAN KUAT LENTUR BETON DENGAN MUTU Fc’ 25 MEGAPASCAL (MPa)

Along with the development of the times in the construction sector, there are so many new innovations in the infrastructure sector. The use of concrete construction is in demand because concrete has beneficial properties such as fire resistance, durability, high compressive strength and in practice it is easy to shape into the desired shape. Concrete material consists of a mixture of cement, coarse aggregate, fine aggregate, water and sometimes with innovative additives. The research method used in this research is experimental, by making sample test objects in the laboratory using two different specimens but with the same concrete quality, namely fc'25 MPa. Based on the results of the values ​​on the flexural and compressive test specimens in the laboratory, it has been found that an unsuitable relationship between flexural strength (fs) and compressive strength (fc ') is in accordance with SNI 2847: 2013. The formula (fr = 0.62) applies to the 28-day-old concrete test.

Local compression behavior of UHPFRC: Experiments and bearing capacity calculation model

To evaluate the mechanical properties of the anchorage zone of prestressed UHPFRC structure, an experimental study was conducted on 54 UHPFRC specimens with central channels using local pressure tests. The local compression bearing capacity and load–displacement relationship were obtained. The experimental results indicated that there were four stages of local compression behavior in specimens: compaction, elastic deformation, crack development in the peripheral concrete and its interface with the wedge, and failure. The local compression cracking load of UHPFRC specimens was generally 40%-80% of the ultimate load. The local compression area ratio had a large effect on the vertical stiffness of UHPFRC local compression specimens. The increase in steel fiber length-diameter ratio (from 65 to 80) improved the transverse flexibility of the specimens. The average increases of UHPFRC local compression cracking load and ultimate load were up to 18.81% and 10.04% when the steel fiber volume content increases from 1% to 3%. The increase of the local compression area ratio on the local compression bearing capacity of UHPFRC ranged from 0.10% to 30.93%. Finally, the analytical formula was proposed to calculate the local compression bearing capacity of UHPFRC by fully considering the effect of the tensile strength of UHPFRC on the hooping action of peripheral concrete. This research provided a novel insight into the accurate bearing capacity calculation methods for UHPFRC in anchorage zones.

On the use of the Combined Loading Compression fixture to estimate the intralaminar compressive fracture toughness of composites

This study reassesses the constraint effect provided by a Combined Loading Compression (CLC) fixture on notched specimens used to measure the compressive intralaminar fracture toughness of composite materials. An experimental campaign is carried out to determine whether a variation in the specimen gauge section length would result in a significant change in the nominal strength of Double Edge Notch CLC specimens. Following the testing of six sets of different specimen geometries for both a uni-directional thermoplastic and a bi-directional woven thermoset composite, the effect of the gauge length is analysed using the size-effect method. Results show that nominal notched strength variation is minimal, suggesting that the CLC clamp does not effectively constrain the gripped sections against in-plane deformations. This assessment proves that the correction factor used in the determination of the R-curve needs to be computed considering the entire specimen geometry, including the gripped regions. Furthermore, the results reveal that previous characterisation campaigns conducted using end-loaded Double Edge Notch Compression specimens could have led to a significant underestimation of the steady-state fracture toughness.

ANALISIS MUTU BETON TERHADAP BETON PASCA BAKAR

A fire is an unwanted disaster, in the framework of a post-fire building structure it becomes the basis for deciding whether the building structure can still be used or not. The rise in high temperatures in concrete structures will result in changes in concrete, the problem faced is how to handle post-fire buildings. From this explanation, this research will discuss the strength of concrete structures, especially the ratio of normal concrete to concrete that has been burnt with variations in duration of burning 1 hour, 2 hours and 3 hours under normal conditions. Concrete compressive strength testing was carried out when the specimens reached the age of 3 days, 7 days, 14 days, 21 days, and 28 days with cylindrical specimens and the flexural strength of concrete was carried out when the specimens reached 28 days. The number of concrete compressive strength test specimens is 36 unit, and the flexural strength is 12 unit. The normal quality of concrete used is 30 MPa. From the results of the analysis regarding the tests carried out on compressive strength, it can be concluded that from the results of the compressive strength tests of 1 hour, 2 hours and 3 hours it decreased by 26.83%, 41.46% and 59.67% compared to concrete normal, for the flexural strength test results of 1 hour, 2 hours, and 3 hours decreased by 33.25%, 66.75%, and 66.75% compared to normal concrete.