In this study, the Charpy impact toughness of three austenitic high-Mn steels was evaluated at room and cryogenic temperatures, and interpreted by deformation mechanisms in relation to the ...microstructural evolution of dynamically compressed specimens. Under dynamic compressive loading, nanocell structures composed of subgrains were formed by the reaction with twins and dislocations, and resulted in a high-strain-rate deformation mechanism that enhanced the strength, ductility and toughness within the stacking fault energy (SFE) range of the twinning-induced plasticity (TWIP) mechanism at room temperature. At cryogenic temperature, the formation of nanocell structures was activated with increasing Mn content, which showed the opposite trend to the room-temperature case. Since the cryogenic-temperature SFEs were lower by 30% than the room-temperature SFEs, a considerable amount of epsilon -martensite was formed in the 0.4C-22Mn steel by the transformation-induced plasticity (TRIP) mechanism, while the TWIP mechanism was working, thereby leading to increased Charpy toughness compared to the 0.4C-24Mn and 0.4C-26Mn steels. The Charpy impact toughness results were discussed using a new schematic diagram of deformation mechanisms based on SFE, loading condition and test temperature.
•FG exhibits excellent energy absorption under quasi-static and dynamic compression.•Higher FG density enhances energy absorption but also increases peak strength.•FG with 20% GBFS exhibits superior ...energy absorption and load transfer.•Rising strain rate greatly increases peak strength but minor effect on plateau stress.•Proposed DIF reasonably predicts peak strength of FG under different strain rates.
To assess the potential for substituting foam concrete with low-carbon foamed geopolymer (FG) in the field of structural protection, a series of quasi-static and dynamic compression tests were conducted. These tests aimed to examine the mechanical performance and energy absorption of FG while considering the factors of FG density, granulated blast furnace slag (GBFS) replacement rate, and water–solid ratio. Additionally, supplementary investigations involving XRD analysis, indentation tests, X-CT scanning, and 3D reconstruction techniques were conducted to explore the influence of GBFS replacement rate on the energy absorption of FG in terms of base material properties and internal pore structure. The results of the quasi-static compressive tests showed that increasing the FG density and reducing the water–solid ratio had a positive effect on energy absorption, however, it also resulted in a notable increase in peak strength. Increasing the GBFS replacement rate not only enhanced the load-bearing capacity but also increased the extent of spalling damage, thus FG with a moderate GBFS replacement rate of 20% demonstrated superior performance in terms of energy absorption and load transfer. Under dynamic compression, all specimens predominantly experienced vertical splitting failure. However, with increasing loading velocity, crushing failure emerged at the two ends of the specimens, particularly in the case of low-density specimens. As the loading velocity increased, the specimen exhibited a significant increase in peak strength, demonstrating a notable strain rate effect, however, the energy absorption of the specimen remained relatively stable without significant alterations. In addition, a simplified DIF was proposed to predict the peak strength of FG with varying densities and two distinct GBFS replacement rates under different strain rates. It provided some valuable insights into the potential application of FG in the field of structural protection.
In the present study, Charpy impact energy (ET) composed of fracture initiation energy (EI) and propagation energy (EP) of austenitic Fe–(0.4,1.0)C–18Mn steels was evaluated in the temperature range ...from room to cryogenic temperatures by an instrumented Charpy impact tester, and was interpreted by microstructural evolution of dynamically compressed specimens. In the 1.0C–18Mn steel, the EI and EP decreased slightly with decreasing temperature, but the EP/ET ratio was kept to be about 0.5. In the 0.4C–18Mn steel, the EI remained almost constant or slightly decreased with decreasing temperature, while the EP/ET ratio steadily decreased, thereby leading to the lower (about 30%) cryogenic-temperature ET than that of the 1.0C–18Mn steel. Under the dynamic compressive loading, a considerable number of ε-martensites were formed in the 0.4C–18Mn steel, whereas they were not found in the 1.0C–18Mn steel, and their volume fractions increased steadily with decreasing temperature. This γ→ε-martensite transformation was attributed to the decrease in stacking fault energy, and resulted in the very low EP and resultant ET.
This paper describes the comparison between compressive behaviour of a commercial Ultra High-Performance (Fibre-Reinforced) Concrete, having 3% content of high carbon straight steel fibres, and its ...matrix. A special device named 3D-Modified Hopkinson Bar (3D-MHB) installed in the DynaMat SUPSI Laboratory was used to test cylindrical specimens with 30 mm diameter and height/diameter ratios of 1, 1.5 and 2. Experimental results were compared to those obtained numerically using the DAMP explicit material model, which can accurately represent multiple dynamic scenarios in structural analysis.
The aluminium-matrix composites (AMCs) consisted of (5, 10 and 15) x/% SiC particles (SiCp) in an aluminium alloy 7055 matrix. Specimens were taken from hot-press sintering. High-strain-rate tests ...were performed using the split-Hopkinson pressure bar (SHPB) method. The microstructures were observed with a scanning electron microscope (SEM) to understand the damage mechanisms of the SiCp/7055 Al composites at high strain rate. The SHPB test results show that the SiCp-reinforced composites are more sensitive to strain rate than the unreinforced material. The strain-rate sensitivity of the flow stress of these composites increases substantially with the increase of the strain rate. The flow stress of SiCp/7055Al composites with 10 x/% and 15 x/% SiCp at 3000 s–1 first increases and then decreases with the increase of the plastic strains, which was caused by the heat generated during adiabatic compression. Microstructure-characterization results show that SiCp cracking and SiCp/7055Al interface debonding are the main damage mechanisms of the composites. The SiCp volume fraction and strain rate affect the damage of composites during the dynamic compressive deformation of the SiCp /7055Al composites.
Room- and cryogenic-temperature compressive properties for the three V10Cr10Co30FexNi50-x (x = 40, 45, 50) high entropy alloys are investigated under quasi-static and dynamic loading conditions. The ...face-centered cubic (FCC) stability, which is estimated by the calculation of Gibbs free energy difference between FCC and body-centered cubic (BCC) phases, decreases in increasing order of Fe content. The 40Fe and 45Fe alloys consist of FCC single phase, whereas the 50Fe alloy is composed of a duplex structure with ~95 vol% of body-centered cubic (BCC) lath martensite. Under the quasi-static loading condition at room temperature, the dislocation slip prevails in the 40-at.%-Fe-containing alloy, while the twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) are activated in the other alloys. The decrease in testing temperature lowers the FCC stability, activating both TWIP and TRIP mode. Under the dynamic loading, the magnitude of TWIP effect enhances, but that of TRIP effect reduces in comparison to the quasi-static loading. The adiabatic heating induced from the dynamic loading increases the FCC stability, thereby resulting in the reduced TRIP effect. Despite the increased stability, the TWIP occurs more actively because the dynamic loading enables the increased flow stress to readily exceed the critical stress required for TWIP. These variations of deformation mechanisms according to the FCC stability, testing temperature, loading rate, adiabatic heating effect, and increased flow stress effect are systematically correlated by the shifting of stability on the slip-TWIP-TRIP mechanism band.
NaOH and sodium silicate-activated slag and fly ash based geopolymer concrete (NSSFGC) and NaOH and Na2CO3-activated slag and fly ash based geopolymer concrete (NNSFGC) with strength grades of C30 ...were prepared, the dynamic compressive deformation behavior under impact loading was studied contrastly. The results indicate that, the compressive deformation of NSSFGC is greater than that of NNSFGC in the stage of compaction, which indicates that the volume of microdefect of NSSFGC is greater than that of NNSFGC; the elasticity modulus of NNSFGC is larger than that of NSSFGC; NSSFGC has excellent deformation performance. Thus it can be seen that, alkali-activator types have a big impact on the dynamic compressive deformation behavior of GC, and compared to the alkali-activator prepared with NaOH and Na2CO3, the alkali-activator prepared with NaOH and sodium silicate can be beneficial to give full play to deformation property; so it is better to prepare GC with NaOH and sodium silicate, when used in the Earthquake Engineering.
•Alkali-activated slag and fly ash based geopolymer concrete was prepared.•The dynamic compressive deformation behavior under impact loading was studied.•The application prospect has been discussed.•The reasonable suggestions on the application of geopolymer concrete have been put forward.•It is better to prepare geopolymer concrete with NaOH and sodium silicate, when used in the Earthquake Engineering.
•The energy-absorption indicators under different strain rate have been obtained.•The energy-absorbing features and effect of basalt fiber have been analyzed.•Basalt fiber has obvious improving ...effect on the toughness of porous material.•Basalt fiber can improve the energy-absorbing ability of porous material.•Basalt fiber has a promising future in the feature improving field.
Ceramics–cement based porous material (CCPM) and basalt fiber reinforced ceramics–cement based porous material (BFRCCPM) have been prepared. The quasi-static compression test and impact compression test of both CCPM and BFRCCPM have been made and the energy-absorption indicators under different strain rate have been obtained. The energy-absorbing features of them have been comparatively analyzed and the effect of basalt fiber has been comparatively studied. The results show: under quasi-static compression state, the peak toughness and full toughness increase continuously with strain rate. Under the same strain rate, the peak toughness of BFRCCPM are obviously higher than that of CCPM. It is because basalt fiber can increase the peak toughness and full toughness. During impact compression stage, the peak toughness and specific energy absorption are highly strain rate sensitive and increase continuously with it. Basalt fiber has obvious improving effect on both peak toughness and full toughness. During impact compression state, the more energy the specimen absorbs, the more seriously it is damaged. BFRCCPM is comparatively slightly damaged given the same amount of absorbed energy. It is because the important effect of the basalt fiber. So, it can be concluded that basalt fiber can improve the energy-absorbing ability of porous material and has a promising future in the feature improving field.
The rapid development of modern society has increased the demand for high-performance geo-materials. As an advanced cementitious composite, fiber-reinforced concrete has attracted much attention and ...has been widely applied to various buildings and civil infrastructure. A basalt fiber-reinforced concrete is proposed as an advanced geo-material and the mechanical and thermal properties were investigated in this study. The basalt fiber-reinforced concrete was compared with ordinary concrete to confirm its superiority by determination of the physical parameters, static compressive test, and dynamic compressive test. The static compressive test was performed using the YAW-2000C constant stress pressure experimental machine under different heating temperatures and cooling methods, while the dynamic compressive test was performed using the 75-mm split-Hopkinson pressure bar under different loading rates, heating temperatures, and cooling methods. For the basic physical parameters, it was found that the mass loss and wave velocity of concrete decrease with the increase of the temperature. In the static compressive test, the static compressive strength for both the ordinary concrete and the fiber-reinforced concrete decreased with the increase of the temperature, and greater strength was observed with the air-cooled compared to the water-cooled method. It was found that the strength of basalt fiber-reinforced concrete is greater than that of ordinary concrete. In the dynamic compressive test, the strength increased with an increasing loading rate and descended with an increasing temperature, while for the same heating temperature and loading rate, water cooling produced more irregular and smaller fragments than air cooling. The dynamic compressive strength of basalt fiber-reinforced concrete was bigger than that of ordinary concrete.
A 7075 Al alloy matrix composite reinforced with SiC particulates (SiC
p
s) whose sizes were 10 and 30 μm, i.e., a bimodal Al–SiC
p
composite, was made by a liquid pressing process, and its ...quasi-static and dynamic compressive properties were evaluated by using a universal testing machine and a split Hopkinson pressure bar, respectively. Mg–Si-, Al–Fe-, and Cu-rich intermetallic compounds existed inside the Al matrix, but might not deteriorate compressive properties because of their low volume fraction (about 2.6%) which was much lower than that of SiC
p
. The dynamic compressive strength was higher than the quasi-static strength, and was higher in the specimen tested at 2800 s
−1
than in the specimen tested at 1400 s
−1
according to the strain-rate hardening. For explaining the strain data, the blocking extent of crack propagation by the Al matrix was quantitatively examined. The melting of Al matrix occurred by adiabatic heating was favorable for the improvement in compressive strain because it favorably worked for activating the shear band formation and for blocking the crack propagation, thereby leading to the excellent compressive strain (10.9–11.6%) as well as maximum compressive strength (1057–1147 MPa). Thus, the present bimodal 7075 Al–SiC
p
composite provides a promise for new applications to high-performance armor plates.
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