Compression Experiments Research Articles

Mechanical behaviour of ductile polymer cellular model structures manufactured by FDM

In this work, Acrylonitrile-Butadiene-Styrene model structures were manufactured by FDM, and their mechanical behaviour investigated under compression, both at small and at large strains. The structure design strategy adopted, based on the use of circular cross-section beam-like elements formed under controlled conditions, led to obtain open-cell structures (with a porosity degree of ≈ 65%) composed of unit cells with different shapes and dimensions assembled to form regularly repeating patterns. The stress-strain behaviour, from cube- and prism-shaped specimens with different sizes and loaded along different directions, was discussed in the light of the outcomes from (i) cyclic compression experiments and (ii) morphological analyses of cryogenic fracture surfaces of specimens compressed at high strain levels. The response along the 3D-stacking direction was traced back to the elastic-plastic case, with non-recoverable strain starting to accumulate between 3% and 5% strain and structure densification starting below 20%. The specimen size effects turned out to be little pronounced. Slightly higher levels of stiffness and strength were measured for the largest cube. This result was discussed on the basis of the peculiar morphology of the structure examined.

Mechanical behaviors of three-dimensional chiral mechanical metamaterials

Chiral and achiral mechanical metamaterials are designed via spherical tiling. The 3D chiral designs show an interesting coupled compression-twisting behavior, while the 3D achiral designs show auxetic behavior. Also, besides the cellular-type chiral and achiral designs, composite-type of each design are created by adding soft matrix to the cellular designs. The designs are fabricated via multi-material 3D printing. Mechanical uni-axial compression experiments are performed on the 3D printed specimens and the experimental results are compared with finite element (FE) simulations. By jointly tailoring the chiral geometry and material combination, the effective mechanical properties and the deformation mechanisms can be tuned in a large range. In addition, a continuum-level material model was developed to predict the constitutive relationship. The results show that the material model can well predict the effective mechanical properties of the chiral 3D mechanical metamaterials.

Quantifying uncertainty in analysis of shockless dynamic compression experiments on platinum. II. Bayesian model calibration

Dynamic shockless compression experiments provide the ability to explore material behavior at extreme pressures but relatively low temperatures. Typically, the data from these types of experiments are interpreted through an analytic method called Lagrangian analysis. In this work, alternative analysis methods are explored using modern statistical methods. Specifically, Bayesian model calibration is applied to a new set of platinum data shocklessly compressed to 570 GPa. Several platinum equation-of-state models are evaluated, including traditional parametric forms as well as a novel non-parametric model concept. The results are compared to those in Paper I obtained by inverse Lagrangian analysis. The comparisons suggest that Bayesian calibration is not only a viable framework for precise quantification of the compression path, but also reveals insights pertaining to trade-offs surrounding model form selection, sensitivities of the relevant experimental uncertainties, and assumptions and limitations within Lagrangian analysis. The non-parametric model method, in particular, is found to give precise unbiased results and is expected to be useful over a wide range of applications. The calibration results in estimates of the platinum principal isentrope over the full range of experimental pressures to a standard error of 1.6%, which extends the results from Paper I while maintaining the high precision required for the platinum pressure standard.

Hot Deformation Behavior and Microstructural Evolution of the As-rolled 7050Al Alloy

The hot deformation behavior of the as-rolled 7050 aluminum alloy was investigated using isothermal hot compression experiments with temperatures ranging from 300 to 460 °C and strain rates ranging from 0.001 to 1 s−1, up to a total strain of 1.1. A strain-compensated Arrhenius (SCA) model was established based on the experimental flow stress data. The predictive accuracy of the model was numerically evaluated using the Correlation Coefficients (R) and the Average Absolute Relative Error (AARE). Electron backscatter diffraction (EBSD) was used to characterize the effects of strain rate and compressive temperature on the microstructure evolution and recrystallization behavior. The results indicated that the geometric dynamic recrystallization (GDRX) occurred at high strain rates or low temperatures, while continuous dynamic recrystallization (CDRX) became the dominant recrystallization mechanism with increasing deformation temperature and decreasing strain rate. The work hardening effect was enhanced during the later stage of deformation, and discontinuous dynamic recrystallization (DDRX) became the main recrystallization mechanism.

Quantifying uncertainty in analysis of shockless dynamic compression experiments on platinum. I. Inverse Lagrangian analysis

Absolute measurements of solid-material compressibility by magnetically driven shockless dynamic compression experiments to multi-megabar pressures have the potential to greatly improve the accuracy and precision of pressure calibration standards for use in diamond anvil cell experiments. To this end, we apply characteristics-based inverse Lagrangian analysis (ILA) to 11 sets of ramp-compression data on pure platinum (Pt) metal and then reduce the resulting weighted-mean stress–strain curve to the principal isentrope and room-temperature isotherm using simple models for yield stress and Grüneisen parameter. We introduce several improvements to methods for ILA and quasi-isentrope reduction, the latter including calculation of corrections in wave speed instead of stress and pressure to render results largely independent of initial yield stress while enforcing thermodynamic consistency near zero pressure. More importantly, we quantify in detail the propagation of experimental uncertainty through ILA and model uncertainty through quasi-isentrope reduction, considering all potential sources of error except the electrode and window material models used in ILA. Compared to previous approaches, we find larger uncertainty in longitudinal stress. Monte Carlo analysis demonstrates that uncertainty in the yield-stress model constitutes by far the largest contribution to uncertainty in quasi-isentrope reduction corrections. We present a new room-temperature isotherm for Pt up to 444 GPa, with 1-sigma uncertainty at that pressure of just under ±1.2%; the latter is about a factor of three smaller than uncertainty previously reported for multi-megabar ramp-compression experiments on Pt. The result is well represented by a Vinet-form compression curve with (isothermal) bulk modulus K0=270.3±3.8 GPa, pressure derivative K0′=5.66±0.10, and correlation coefficient RK0,K0′=−0.843.

Axial compression experiment and numerical simulation of CFST short columns at an ultra early age

To study the axial compression performance of ultra-early-age concrete-filled steel tube (CFST) short columns, axial compression tests were carried out on short columns of CFSTs with different wall thicknesses of steel tubes and different concrete ages. The load-displacement curves and failure modes of CFST short column specimens under different concrete ages were obtained. The influence of wall thickness and concrete age on the mechanical properties of ultra-early-age CFST specimens was analyzed. The calculation formula for the bearing capacity of mature CFST short columns in GB50936–2014 was extended, and a new calculation formula for calculating the bearing capacity of ultra-early-age CFST short columns was proposed. Considering that there is no known concrete stress-strain expression for ultra-early-age CFST short columns in existing literature, this paper has adjusted the constitutive model of the core concrete in ordinary CFSTs and advanced a stress-strain relationship suitable for the core concrete in ultra-early-age CFST short columns.

Constitutive relationship and fracture mechanism for wide stress triaxiality of titanium alloy

It is necessary to determine the fracture criteria and parameters that conform to the plastic deformation and fracture mechanism of titanium alloy under wide stress triaxility. Fourteen different shapes and notch specimens were designed for uniaxial tensile and compression experiments. Based on the analysis of plastic behavior and fracture mechanism, the Swift-Voce hardening model, CPB06 yield criterion and DF2016 fracture criterion were respectively established. The fracture parameters of the ductile fracture model were calculated by the analytic equation solving method. The fracture behavior of forged TC4 titanium alloy was successfully predicted by finite element software. The research results showed that the dimples of fracture morphology become larger and deeper with the increase of stress triaxiality, and the ductile fracture mechanism changes from shear fracture to dimple fracture mechanism. The comparison of experiment and simulation indicated that the Swift-Voce hardening model and CPB06 yield criterion reasonably simulate the plastic deformation. It also proved the DF2016 model can provide the most accurate prediction of fracture behavior for forged TC4 alloy under different stress states.

Multi-scale failure mechanisms of hydraulic engineering exposed to seasonally frozen salinization environment: Integrating SBAS-InSAR and mechanical experiments

Constructing hydraulic engineering ensures agricultural development and improves salinization environments. However, in seasonally frozen salinization regions, hydraulic engineering is prone to deformation failure. Leakage from canal raises the regional groundwater level, triggering secondary salinization environmental issues. Exploring the instability mechanisms is thus necessary for hydraulic engineering. Traditional deformation monitoring techniques and soil experiments are constrained by observation scale and timeliness. In this study, Sentinel-1B data from November 2017 to August 2019 were acquired. The small baseline subset (SBAS) InSAR approach was employed to interpret the seasonal deformation characteristics in both the vertical and slope directions of a damaged canal segment in Songyuan, Northeast China. The mechanical properties of saline-alkali soil under varying water contents were quantified by integrating unconfined compression experiment (UCE). In May, as the soil thawed downward, a frozen lenses with poor permeability formed at a depth of approximately 100 cm, causing the accumulation of meltwater and infiltrated precipitation between the frozen layer and the melting layer in the canal. The soil water content at a depth of 80 to 140 cm exceeded 22 %, reaching a threshold for rapid reduction in unconfined compression strength (UCS). Consequently, in spring, the low soil strength between the frozen layer and the melting layer resulted in interface sliding, with a displacement of −133.88 mm in the canal slope direction. Furthermore, the differential projection of freeze-thaw deformation in the slope direction caused continuous creep of the canal towards the free face, with a value of −23.27 mm, exacerbating the formation of the late spring landslide. Integrating InSAR and engineering geological analysis is beneficial for addressing deformation issues in hydraulic engineering. Ensuring the sustainable operation of hydraulic engineering holds important implications for mitigating the salinization process.

Discontinous and continuous dynamic recrystallization of Fe-12.5Cr–4Al–2Mo-0.03Nb-0.08Y alloy during hot deformation

The hot deformation behavior and microstructure of Fe-12.5Cr–4Al–2Mo-0.03Nb-0.08Y alloy were studied under conditions of 800 °C–1200 °C/0.01 s−1∼10 s−1 using a combination of hot compression experiments, EBSD and TEM characterization. The results indicate that the deformation temperature and strain rate have a significant impact on the flow stress and microstructure of the alloy, especially the deformation temperature. The constitutive equation constructed in this paper can reflect the hot deformation process and accurately calculate flow stress value of the FeCrAl alloy in corresponding states. The FeCrAl alloy undergoes DRV and DRX during hot deformation. DDRX grains distributed along the original grain boundaries mainly formed at low deformation temperatures and high strain rates, while CDRX grains mainly formed at high deformation temperatures and low strain rates and characterized by the internal distribution of the original grains. Moreover, the orientation of DDRX grains is mostly different from that of adjacent original grains, while the orientation of CDRX grains is relatively close to that of the original grains.

An embedded digital element model to simulate the wrinkle defects driven by the consolidation of composites

Understanding the mechanisms of fiber wrinkling during the compaction process is of paramount importance as fiber wrinkling significantly affects the mechanical properties of composite materials. This study introduces an embedded digital element model for simulating the consolidation process of prepreg. Flexible digital element chains are employed to simulate the reinforcing effect of fibers on resin, accounting for the viscoelastic constitutive behavior of uncured resin. The simulation captures intra-layer wrinkles and in-plane waviness defects in the consolidated prepreg, thereby uncovering the mechanism behind fiber wrinkle formation during composite material prepreg consolidation. The accuracy of the model is validated through compression experiments on flat plates and L-shaped structures. The results demonstrate that the proposed embedded digital element model accurately predicts wrinkle defects. Factors such as interlayer friction of the prepreg, consolidation temperature, and mold curvature radius significantly influence the shape and size of wrinkles.

Mechanical, energy evolution, damage and microstructural behavior of cemented tailings-rock fill considering rock content and size effects

Cemented tailings-rock fill (CTRF) is crucial for engineering intention and durability of re-filled stopes in deep underground mines. The current work examined the effects of fragment contents and sizes on the mechanical, energy evolution and microstructure of CTRF with 70 wt% solid. All CTRFs were subjected to uniaxial compression, energy dissipation and scanning electron microscopy experiments. Strength outcomes exhibit that adding rock fragments to CTRF had a clear mitigating influence on the backfill strength. Total/elastic-strain energy at peak point decreased with growing rock content in backfill. SEM-EDS studies demonstrate that backfill defects were chiefly micro-porosity and fractures. The findings are of great significance to guarantee the success and security of the CTRF fulfilled in deep underground hard rock and metalliferous mines.

Mechanical Properties and Energy Absorption of Integrated AlSi10Mg Shell Structures with BCC Lattice Infill

Shell-infill structures comprise an exterior solid shell and an interior lattice infill, whose closed features yield superior comprehensive mechanical performance and light weight. Additive manufacturing (AM) can ensure the fabrication of complex structures. Although the mechanical behaviors of lattice structures have been extensively studied, the corresponding mechanical performances of integrated-manufactured shell structures with lattice infills should be systematically investigated due to the coupling effect of the exterior shell and lattice infill. This study investigated the mechanical properties and energy absorption of AlSi10Mg shell structures with a body-centered cubic lattice infill fabricated by AM. Quasi-static compressive experiments and corresponding finite element analysis were conducted to investigate the mechanical behavior. In addition, two different finite element modeling methods were compared to determine the appropriate modeling strategy in terms of deformation behavior. A study of different parameters, including lattice diameters and shell thicknesses, was conducted to identify their effect on mechanical performance. The results demonstrate the mechanical advantages of shell-infill structures, in which the exterior shell strengthens the lattice infill by up to 2.3 times in terms of the effective Young’s modulus. Increasing the infill strut diameter can improve the specific energy absorption by up to 1.6 times.

Influence of Cargo Luggage on the Vertical Drop Crashworthiness of Aircraft Mid-Fuselage Section

The evaluation of structural crashworthiness is important for the development of civil aircraft. In this study, cargo luggage was considered in the vertical drop simulation of an aircraft mid-fuselage section. First, quasi-static compression tests on three types of luggage made of different materials were conducted. Then, a finite element model (FEM) of the cargo luggage was developed with a crushable foam material in LS-PrePost4.5 software. The finite element analysis results of the luggage made of different materials were consistent with the corresponding compression experiments. Secondly, the FEM of the mid-fuselage section was established without cargo luggage. The simulated displacement and acceleration of the fuselage section were consistent with the test results. Finally, the influences of cargo luggage on the fuselage vertical drop response were studied with the FEM considering both the fuselage structure and cargo luggage. Compared with the responses of the fuselage without cargo luggage, the cargo luggage could reduce the deformation of the cargo bay and maintain the integrity of the passenger living space in the cabin at the vertical velocity of 6 m/s, even though the initial kinetic energy was higher.

Influence of lithology and bedding orientation on failure behavior of “D” shaped tunnel

To explore the influence of lithology on the failure behavior of layered tunnel, true triaxial compression experiments were undertaken on cubical phyllite and yellow sandstone samples containing a “D” shaped hole. The failure progress of the hole sidewalls was monitored and captured using a miniature camera. The results reveal that the initial vertical failure stress of the phyllite samples presents a “U” shaped change as the bedding angle increases. At the bedding angle of 45°, compared with the initial vertical failure stress of the yellow sandstone tunnel, that of the phyllite tunnel is lower, resulting in larger rock fragments and deeper V-shaped grooves. The failure pattern of the phyllite tunnel is primarily manifested as extensive shear sliding failure, and the failure is more severe. The failure of the yellow sandstone tunnel is primarily characterized by the sequential laminar fracturing along the maximum principal stress direction, predominantly manifesting as tensile failure. The primary factors influencing the failure of two types of layered rocks are the significant variations in the clay mineral content within the rocks. For the phyllite, it contains nearly one-third of montmorillonite (a clay mineral). This results in the formation of weak bedding planes within surrounding rocks, which induces shear slip failures along these bedding planes. In contrast, the yellow sandstone has a lower clay mineral content, leading to the absence of distinct weak bedding planes within the surrounding rock. In this case, bedding planes present ignorable effect on the surrounding rock.

Study on thermal deformation constitutive model of NiCoFeAlCrMo high-entropy alloy with FCC / L12 coherent structure

Due to its multi-principal component characteristics, high-entropy alloys exhibit excellent comprehensive mechanical properties and become a new generation of engineering structure alternative materials. At present, a single constitutive model is used to describe the change of flow stress in the study of hot deformation behavior of high-entropy alloys, and there are some problems such as inaccurate prediction accuracy or inapplicability of the model in some hot processing intervals. In this paper, three different constitutive models are combined to fully consider the applicability of the model in different temperature ranges, and the change of flow stress behavior is accurately described, which is of great significance for subsequent deformation mechanism research, hot processing process optimization, numerical simulation and so on. Thermal compression experiments on cast Ni28.5Co18.6Fe18.2Al16.3Cr10.5Mo4 Ti2.3Nb0.6W0.9C0.2 high-entropy alloy were carried out using a Gleeble-3800 thermal simulation tester with deformation temperatures in the range from 900 ℃ to 1150 ℃ and strain rates from 0.001 s−1 to 1 s−1. The constitutive relationships between true stress and strain, temperature and strain rate were established, while the heat deformation process of this alloy under different deformation conditions by Arrhennius, Modified Johnson-Cook and Modified Fields-Backofen models were characterized. The results indicate that Arrenius model describe the rheological behavior of the alloy better in a wider temperature range and at a wider strain rate range. Comparatively, the model shows the highest prediction accuracy in the high-temperature region and slightly lower accuracy in the mesothermal and low-temperature regions. The modified J-C and F-B models have better prediction accuracy in the low-temperature and medium-temperature regions, respectively. Due to the different deformation conditions, dislocation configurations such as dislocation tangles, dislocation networks, and subcrystalline junctions can be observed in the plastic deformation region. The dislocation density of this alloy increases with increasing strain rate and decreasing deformation temperature after deformation.

Bone mineral density estimation from a plain X-ray image by learning decomposition into projections of bone-segmented computed tomography.

Osteoporosis is a prevalent bone disease that causes fractures in fragile bones, leading to a decline in daily living activities. Dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) are highly accurate for diagnosing osteoporosis; however, these modalities require special equipment and scan protocols. To frequently monitor bone health, low-cost, low-dose, and ubiquitously available diagnostic methods are highly anticipated. In this study, we aim to perform bone mineral density (BMD) estimation from a plain X-ray image for opportunistic screening, which is potentially useful for early diagnosis. Existing methods have used multi-stage approaches consisting of extraction of the region of interest and simple regression to estimate BMD, which require a large amount of training data. Therefore, we propose an efficient method that learns decomposition into projections of bone-segmented QCT for BMD estimation under limited datasets. The proposed method achieved high accuracy in BMD estimation, where Pearson correlation coefficients of 0.880 and 0.920 were observed for DXA-measured BMD and QCT-measured BMD estimation tasks, respectively, and the root mean square of the coefficient of variation values were 3.27 to 3.79% for four measurements with different poses. Furthermore, we conducted extensive validation experiments, including multi-pose, uncalibrated-CT, and compression experiments toward actual application in routine clinical practice.

Influence of Lateral Pressure on the Mechanical Performance of Bolted Specimens under Biaxial Compression

The influence of lateral pressure (σ2) on the stability of the surrounding rock of roadway increases after excavation. The rock bolt is usually used to improve the stability of the surrounding rock. Therefore, it is important to understand the biaxial compressive behaviors of the bolted samples influenced by lateral pressure. In this study, biaxial compression experiments are carried out to investigate the biaxial compressive properties of bolted rock samples influenced by lateral pressure. The results show that bolting can improve the peak strength, inhibit the post-peak strength attenuation and reduce the pre-peak brittleness of the bolted rock mass. With the increase of lateral pressure, the strength and elastic modulus of the bolted samples increases approximately parabolic and linearly, respectively. The failure modes of the bolted samples influenced by lateral pressure can be divided into splitting failure and compression-shear failure. A reinforcement mechanism of bolt is observed, namely axial action, axial and transverse action at the pre- and post-peak stages of the bolted samples. Based on a modified true triaxial Mohr-Coulomb strength criterion and this bolt reinforcement mechanism, a new method for calculating the equivalent cohesion and equivalent internal friction angle of the bolted specimens under biaxial compression is proposed. The research results of this paper have certain reference value for the stability control of roadway

Time-resolved Raman spectroscopy for monitoring the structural evolution of materials during rapid compression.

Rapid compression experiments performed using a dynamic diamond anvil cell (dDAC) offer the opportunity to study compression rate-dependent phenomena, which provide critical knowledge of the phase transition kinetics of materials. However, direct probing of the structure evolution of materials is scarce and so far limited to the synchrotron based x-ray diffraction technique. Here, we present a time-resolved Raman spectroscopy technique to monitor the structural evolutions in a subsecond time resolution. Instead of applying a shutter-based synchronization scheme in previous work, we directly coupled and synchronized the spectrometers with the dDAC, providing sequential Raman data over a broad pressure range. The capability and versatility of this technique are verified by in situ observation of the phase transition processes of three rapid compressed samples. Not only the phase transition pressures but also the transition pathways are reproduced with good accuracy. This approach has the potential to serve as an important complement to x-ray diffraction applied to study the kinetics of phase transitions occurring on time scales of seconds and above.

Microstructural and thermal properties of coal measure sandstone subjected to high temperatures

To study the microscopic structure, thermal and mechanical properties of sandstones under the influence of temperature, coal measure sandstones from Southwest China are adopted as the research object to carry out high-temperature tests at 25 °C–1000 °C. The microscopic images of sandstone after thermal treatment are obtained by means of polarizing microscopy and scanning electron microscopy (SEM). Based on thermogravimetric (TG) analysis and differential scanning calorimetric (DSC) analysis, the model function of coal measure sandstone is explored through thermal analysis kinetics (TAK) theory, and the kinetic parameters of thermal decomposition and the thermal decomposition reaction rate of rock are studied. Through the uniaxial compression experiments, the stress‒strain curves and strength characteristics of sandstone under the influence of temperature are obtained. The results show that the temperature has a significant effect on the microstructure, mineral composition and mechanical properties of sandstone. In particular, when the temperature exceeds 400 °C, the thermal fracture phenomenon of rock is obvious, the activity of activated molecules is significantly enhanced, and the kinetic phenomenon of the thermal decomposition reaction of rock appears rapidly. The mechanical properties of rock are weakened under the influence of rock thermal fracture and mineral thermal decomposition. These research results can provide a reference for the analysis of surrounding rock stability and the control of disasters caused by thermal damage in areas such as underground coal gasification (UCG) channels and rock masses subjected to mine fires.

Hot Deformation Behavior and Mechanisms of SiC Particle Reinforced Al-Zn-Mg-Cu Alloy Matrix Composites

A systematic and comprehensive analysis of the hot deformation and mechanisms of SiC particle-reinforced aluminum matrix composites is significant for optimizing the processing of the composites and obtaining the desired components. Based on this, related research on 11 vol% SiCp particle-reinforced 7050Al matrix composites was carried out. Hot compression experiments were carried out on the Gleeble-3500 thermal simulator to study the hot deformation behavior of composites at the temperature of 370–520 °C and strain rate of 0.001–10 s−1. The hyperbolic sine constitutive equation of the material was established, and the processing map was calculated. Combining the typical metallograph and misorientation angle distribution, the microstructure evolution mechanism of composites was analyzed, and the effect of particles on recrystallization behavior was investigated. Under certain process conditions, the dominant deformation mechanism of composites changed from dynamic recovery (DRV) to dynamic recrystallization (DRX), and the grain boundary sliding mechanism began to play a role. In addition, high temperature tensile and elongation at break were tested, and it was found that the dominant form of fracture failure changed from brittle fracture of the particles to ductile fracture of the matrix as the temperature increased.