Compression Apparatus Research Articles

Influence of aggregate content and strain rate on dynamic behaviour and energy consumption characteristics of concrete

Concrete's dynamic performance and energy dissipation are critical areas of interest that are significantly influenced by strain rate and aggregate content. This study investigated concrete's dynamic deformation, strength development and energy dissipation characteristics from specimens containing 0, 32%, 37% and 42% aggregate. These specimens were subjected to impact compression tests using a split Hopkinson compression apparatus, which allowed the effects of strain rate and aggregate content on the deformation, strength and energy dissipation of the concrete to be analysed. The results show that the concrete exhibits deformation hysteresis under impact loading, with splitting tensile failure as the predominant damage mechanism. Dynamic strength was more sensitive to strain rate than aggregate content. The dynamic increase factor (DIF) varied with aggregate content at different strain rates. The extent of specimen damage significantly influenced the energy distribution ratio, with absorbed energy showing a more pronounced strain rate effect than transmitted and reflected energy. Conversely, the amount of transmitted energy had a more pronounced impact on aggregate content than the amount of absorbed and reflected energy.

Fabrication of Apparatus Specialized for Measuring the Elasticity of Perioral Tissues.

On the human face, the lips are one of the most important anatomical elements, both morphologically and functionally. Morphologically, they have a significant impact on aesthetics, and abnormal lip morphology causes sociopsychological problems. Functionally, they play a crucial role in breathing, articulation, feeding, and swallowing. An apparatus that can accurately and easily measure the elastic modulus of perioral tissues in clinical tests was developed, and its measurement sensitivity was evaluated. The apparatus is basically a uniaxial compression apparatus consisting of a force sensor and a displacement sensor. The displacement sensor works by enhancing the restoring force due to the deformation of soft materials. Using the apparatus, the force and the displacement were measured for polyurethane elastomers with various levels of softness, which are a model material of human tissues. The stress measured by the developed apparatus increased in proportion to Young's modulus, and was measured by the compression apparatus at the whole region of Young's modulus, indicating that the relation can be used for calibration. Clinical tests using the developed apparatus revealed that Young's moduli for upper lip, left cheek, and right cheek were evaluated to be 45, 4.0, and 9.9 kPa, respectively. In this paper, the advantages of this apparatus and the interpretation of the data obtained are discussed from the perspective of orthodontics.

Biomechanical properties of the capsule and extracellular matrix play a major role during the Wolffian/epididymal duct development.

The epididymis is important for sperm maturation and without its proper development, male infertility will result. Biomechanical properties of tissues/organs play key roles during their morphogenesis, including the Wolffian duct. It is hypothesized that structural/bulk stiffness of the capsule and mesenchyme/extracellular matrix that surround the duct is a major biomechanical property that regulates Wolffian duct morphogenesis. These data will provide key information as to the mechanisms that regulate the development of this important organ. To measure the structural/bulk stiffness in Pascals (force/area) of the capsule and the capsule and mesenchyme together that surrounds the Wolffian duct during the development. To examine the relative membrane tension of mesenchymal cells during the Wolffian duct development. Since Ptk7 was previously shown to regulate ECM integrity and Wolffian duct elongation and coiling, the hypothesis that Ptk7 regulates structural/bulk stiffness and mesenchymal cell membrane tension was tested. Atomic force microscopy and a microsquisher compression apparatus were used to measure the structural stiffness. Biomechanical properties within the membranes of cells within the capsule and mesenchyme were examined using a membrane-tension fluorescent probe. The structural stiffness (Pascals) of the capsule and underlying mesenchyme was relatively constant during development, with a significant increase in the capsule at the later stages. However, this increase may reflect the ECM and associated mesenchyme being close to the capsule because the coiling of the duct pushed or compressed them into that space. Keeping the capsule and mesenchyme/ECM at constant stiffness would ensure that the duct will continue to coil under similar biomechanical forces throughout the development. Cells within the capsule and mesenchyme at different Wolffian duct regions during the development had varying degrees of membrane lipid tension. It is hypothesized that the dynamic changes ensure the duct is kept at a constant stiffness regardless of any external forces. Loss of Ptk7 resulted in an increase in stiffness at E18.5, which was presumable due to the loss of integrity of the ECM within the mesenchyme. Biomechanical properties of the capsule and the mesenchyme/extracellular matrix that surround the Wolffian duct play an important role toward Wolffian duct morphogenesis, thereby allowing for the proper development of the epididymis and subsequent male fertility.

Development of Improved Confined Compression Testing Setups for Use in Stress Relaxation Testing of Viscoelastic Biomaterials.

The development of cell-based biomaterial alternatives holds significant promise in tissue engineering applications, but it requires accurate mechanical assessment. Herein, we present the development of a novel 3D-printed confined compression apparatus, fabricated using clear resin, designed to cater to the unique demands of biomaterial developers. Our objective was to enhance the precision of force measurements and improve sample visibility during compression testing. We compared the performance of our innovative 3D-printed confined compression setup to a conventional setup by performing stress relaxation testing on hydrogels with variable degrees of crosslinking. We assessed equilibrium force, aggregate modulus, and peak force. This study demonstrates that our revised setup can capture a larger range of force values while simultaneously improving accuracy. We were able to detect significant differences in force and aggregate modulus measurements of hydrogels with variable degrees of crosslinking using our revised setup, whereas these were indistinguishable with the convectional apparatus. Further, by incorporating a clear resin in the fabrication of the compression chamber, we improved sample visibility, thus enabling real-time monitoring and informed assessment of biomaterial behavior under compressive testing.

433 Orientation of the Lumbar Spine During Dynamic Compression Influences Fracture Characteristics

INTRODUCTION: Characteristics of lumbar spine fractures dictate patient outcomes and clinical treatment decisions. Understanding injury biomechanics associated with different fracture types can assist injury prediction and development of safety enhancements. METHODS: Twenty human lumbar spines (T12-L5) were isolated and attached to novel whole-column experimental dynamic compressive loading apparatus. Specimens were attached to the lower platform on a drop tower and a decoupled upper platform held a mass to simulate the torso inertially loading the lumbar spine as the lower platform was decelerated at the drop tower base. Each specimen was tested at increasing deceleration magnitudes until failure. Pre-test x-rays were used for the measurements to quantify spinal orientation. Fractures were classified using post-test x-rays and CT scans. RESULTS: Fractures were classified into six categories [Wedge (AO Spine A1): n = 8, Burst (AO Spine A3/A4): n = 7, Hyperextension (AO Spine B2): n = 5]. Spines that sustained hyperextension fractures had significantly larger Cobb angles compared to spines that sustained burst fracture (p = 0.03). Spines that sustained wedge fracture had significantly larger lumbar spine angles (i.e., closer to vertical orientation) compared to spines that sustained burst (p = 0.03) and hyperextension (p = 0.02) fracture. Spines that sustained wedge fracture also had a nearly significant longer horizontal distance between the T12 centroid and the load location compared to spines that sustained burst fracture (p = 0.07). CONCLUSIONS: This study demonstrated that orientation of the lumbar spine at the time of dynamic load application affected fracture characteristics and, therefore, post-injury spinal stability and patient outcomes. The clinical importance of these findings includes a better understanding of injury mechanisms and a recognition that a wide variety of injury outcomes (stable versus unstable; anterior versus middle versus posterior column) can result from identical loading situations with different spinal orientations.

Measurements of the Permeability Coefficient of Waste Coal Ash under Hydrostatic Pressure to Identify the Feasibility of Its Use in Construction

The aim of this research was to measure the filtration properties of waste coal ash under the influence of hydrostatic pressure generated in a three-axial compression apparatus. The scope of work included determining the compactibility parameters, maximum bulk density and optimal moisture content. Permeability tests were performed for a sample with an average grain composition at three compaction indices IS: 0.964, 0.98 and 1.00. The hydrostatic pressure ranging from 0.5 to 1.8 bar corresponded to the layer depths from 2.17 to 7.83 m. Gradually increasing the pressure during the first loading cycle caused irreversible changes in the structure of the sample by local material agglomeration or grain interlocking. The water permeability coefficient was higher in the second loading cycle than in the first cycle. It was shown that waste coal ash cannot be used as a construction material on its own. To obtain constant filtration properties, the waste coal ash material should be doped, or an optimal compactionshould be used (IS = 1.00). The results presented in this study are important for assessing the use of waste coal ash for construction engineering purposes.

Deformations of bentonite-sand mixture without lateral confining pressure subject to high suctions changing

Generation of electricity in nuclear power plants have supplied further energy to society in the world, and remain arising of radioactive waste as results of performance industry with activity. In fact, all of radioactive waste encourage some categories types as following; two most important points are high-level waste (HLW) and low- and intermediate-level waste (LLW). To end disposal completely, every country operated Nuclear Energy plant foresees further deep geological repository. This study conducted out measurement of deformations due to changing suction, which were volume change, axial strains and radial strains. Used triaxial compression apparatus was improved to be possible controlling suction for air flow circulation, and measured both axial and radial strains and variations of mass under drying-wetting cyclic in suction. Required suction rage is from 2.8 MPa to 296 MPa, and it corresponds to from 98.0 % to 11.0 % in relative humidity. Axial strains and radial strains for all of specimens have described obviously the shrinkage phenomena due to drying and wetting cyclic process regard to suction potential, and bentonite-sand mixture specimens are statically compacted. Axial strains compare that is larger than radial strains regard to all applied suctions. Subsequently, changing of void ratio was classified into two categories, which one was elastic components and other one was plastic component, and elastic component in void ratio was remaining larger than plastic component for high suction ranges.

Shear Strength Analysis and Slope Stability Study of Straight Root Herbaceous Root Soil Composite

The instability of bare slopes is a prevalent concern. The root system of herbaceous vegetation enhances the shear strength of shallow slope soil. This study investigated the mechanism of the root-soil system as well as the effects of different influencing factors on the shear strength of the soil and slope stability. In particular, indoor experiments were conducted on rootless undisturbed soil (RUS) and undisturbed soil with a root system (USRS) using a triaxial compression apparatus to analyze the slope stability of composite soil with a Tagetes erecta root system. Significance tests and correlation analysis of the factors affecting shear performance were conducted. The slope reinforcement effect by the plant root system was simulated under 24 working conditions using the MIDAS finite element method. The results revealed the influence of the root content, moisture content, and stress on the shear strength of USRS, as well as the contribution degree and influence of these variables on the slope stability. Both RUS and USRS exhibited strain hardening during shearing. A strong negative (positive) correlation was observed between the internal friction angle (φ) (cohesion (c)) of the USRS and the root content (moisture content). The maximum deviatoric stress during shear failure of the USRS was 1.29 times higher than that of the RUS. Moreover, the root content was positively correlated with the slope safety coefficient and the slope of the line under different working conditions, whereas the slope angle was negatively correlated with the slope safety coefficient. The reinforcement effect by the root system resulted in a 11.2% increase in the safety coefficient and the improved stability of slopes with an angle larger than 1.5%. The findings of this study provide new insights into shallow slope stability in practical slope protection projects.

Compressive Split Hopkinson Pressure Bar Apparatus: Part I - Design and Development

Optimum utilization of composite materials envisages its use under static as well as dynamic loading conditions. Hence, there is a need to assess the behavior of composite materials at high strain rates. Split Hopkinson Pressure Bar (SHPB) apparatus is widely used to assess high strain rate behavior of composites. Even though SHPB apparatus is widely used, its design methodology and development technique are not readily available. Design and devel- opment details of a compressive SHPB apparatus for characterizing mechanical properties of different materials at high strain rate loading are presented. Brief theoretical background necessary for the design of SHPB apparatus is presented based on one-dimensional wave propagation theory in elastic bars. Next, brief working principle of the apparatus and schematic arrangement are presented. Different components of the compressive SHPB appa- ratus are identified. Design, development and commissioning of the apparatus are discussed. Further, different instruments used and the calibration technique used are presented.

X-ray CT-based numerical investigation of nickel foam-based GDLs under compression

Nickel foams feature superior structural and transport characteristics and are therefore strong candidates to be used as gas diffusion layers (GDLs) in polymer electrolyte fuel cells (PEFCs). In this work, the impact of compression on the key structural and transport properties has been investigated, including employing a specially designed compression apparatus and X-ray computed tomography. Namely, 20 equally spaced two-dimensional CT based images and numerical models have been used/developed to investigate the sensitivity of the key properties of nickel foams (porosity, tortuosity, pore size, ligament thickness, specific surface area, gas permeability and effective diffusivity) to realistic compressions normally experienced in PEFCs. Wherever applicable, the anisotropy in the property has been investigated. One of the notable findings is that, unlike porosity and ligament thickness, the mean pore size was found to decrease significantly with compression. The mean pore size is around 175 μm for uncompressed nickel foam and it decreased to around 110 μm for a 20% compression ratio and to around 70 μm for a 40% compression ratio. Further, unlike the effective diffusivity, the gas permeability was shown to be highly anisotropic with compression; this fact is of particular importance for PEFC modelling where the properties of GDLs are often assumed isotropic. All the computationally estimated properties have been presented, validated and discussed.

Biocementation as a Pro-Ecological Method of Stabilizing Construction Subsoil

The principle of sustainable development imposes an obligation on societies to manage natural resources rationally and to care for the quality of the environment, by, among other things, reducing CO2 emissions. Alternative ways of stabilising building substrates by increasing their shear strength (cu) are increasingly being sought. This paper presents how microorganisms can influence cu and thus the load-bearing capacity of building substrates. Tests were performed in a triaxial compression apparatus in three variants. The first variant of testing was carried out on cemented soil samples, which were cemented in situ. The next two series of tests were performed on reconstructed samples, i.e., natural soil and soil inoculated with a solution of Sporosarcina pasteurii bacteria. The results obtained show that carbonate cementation increases the shear strength of the soil; in addition, this biomineralization-induced cementation gives higher cu results than natural carbonate cementation.

Hydraulic Conductivity Tests in the Triaxial Stress State: Is Peat an Aquitard or an Aquifer?

The characteristics of peat’s are crucial for understanding natural processes and their suitable shaping through the management of water relations. This study focused on the results of one of the first hydraulic conductivity (k) laboratory tests of exemplary peat samples from the Biebrza Valley (a peatland of very high environmental importance) in relation to the stress state and hydraulic gradient. Further, the research was devoted to a specific test procedure of peat permeability as a key feature for landform development in wetlands. Detailed tests of dark brown/black samples were selected as the reference for the research investigations. Four long-term test series of water permeability were performed in a modified triaxial compression apparatus. In all selected hydraulic gradient variants (i = 5,10,25,40,55,85), the k values decreased from 6 × 10−8 m/s to 1.6 × 10−10 m/s with a stepwise increase in the effective confining pressures tested (10, 15, 30, 45, and 90 kPa). These results were related to the inherent soil features—a relatively high peat decomposition and external driver—confining pressure (radial stress) magnitude. Compared to the other Polish peat tests, the determined k values were at the lower end of their hydraulic conductivity range. The analysed organic soil is not a typical aquifer. Despite very high porosities (~88%) and a high organic matter content (81.1–89.4%) which is favourable for water accumulation, the characterized peat showed relatively low hydraulic conductivity values. Thus, this specific soil may differentiate the groundwater flow as it complicates strong contact with surface water.

On the thermal hydro mechanical chemical behavior of bentonite sand mixture

The concept to high-level radioactive waste (HLW) repository generally involves anengineering-artificial barrier system, in which hardly compacted bentonite sand mixture blocks are placed carefully around the waste canister, and the canister is of stiffness in the design. Placed the bentonite sandmixture blocks, gradually receive hydration due to groundwater. Thermal-hydraulic-mechanical-chemical phenomena of compacted bentonite sand mixture after wetting, suction change and thermal effort are a critical parameter for buffered system This study proposes the influence of suction, relative humidity and thermal effort in thermal-hydraulic on deformation properties and mechanical properties for bentonite-sand mixture. A series of testing programs are prepared such as calibration test for changing of relative humiditywith temperatures, measurement of volume change involving heating and changing of suction, determination of unconfined compressive strength, for thermal performance triaxial compression tests for both unsaturated bentonite sand mixture and saturated bentonite sand mixture. The obtained results are further interesting, and summary provide as following. To suction increment incorporation with thermal heating produce induces obviously shrinkage of the bentonite sand mixture, and lead the decrement of strength. Elevated temperature confirm further reduction for maximum deviator stress using a developed triaxial compression apparatus that is regardless of unsaturated condition and saturated condition.

Uncertainty of concrete compressive strength determination by a combination of Rebound Number, UPV and uniaxial compressive tests on cubical concrete samples

Rebound number (RN) and ultrasonic pulse velocity (UPV) determination provide a non-destructive indirect estimation of concrete compressive strength (CS). They have an extensive uncertainty, both due to limited reproducibility and trueness of these methods. Tests on a uniaxial compressive apparatus generate a destructive result, also with a relatively high uncertainty, which requires repeating this test on multiple samples to produce a mean result with an acceptable uncertainty. In this work, a combination of all three methods was performed on cubical concrete specimens. Three different mixes were designed, each corresponding to a different assigned compressive strength. Six specimens were produced from each mix design, and each specimen was cured for 28 days. During and until that time, each specimen was tested according to all three aforementioned methods. Results were compared in pairs and factors related to equipment tolerance and operator variations were assessed. Regression processes were applied to estimate optimized functions that predict compressive strength based on the non-destructive RN and UPV measurements. Additionally, a function was estimated as the mean of all three different test method results. Finally, a statistically significant multivariate function was established along with a corresponding uncertainty budget. The result is a determination of compressive strength for cubical concrete specimen with known, reduced uncertainty. These lower uncertainty limits enable achieving conformity assessment for concrete compressive strength with minimized decision risk. The calibrated multivariate regression function in combination with its resulting uncertainty intervals are expected to benefit constructors in their aim at interpreting their measurement data to comply with the EN 206 quality control procedure and accredited laboratories to verify the validity of their results by performing internal quality control.

HP-TACO: A high-pressure triaxial compression apparatus for in situ x-ray measurements in geomaterials.

Triaxial compression experiments are commonly used to characterize the elastic and inelastic behavior of geomaterials. In situ measurements of grain kinematics, particle breakage, stresses, and other microscopic phenomena have seldom been made during such experiments, particularly at high pressures relevant to many geologic and man-made processes, limiting our fundamental understanding. To address this issue, we developed a new triaxial compression device called HP-TACO (High-Pressure TriAxial COmpression Apparatus). HP-TACO is a miniaturized, conventional triaxial compression apparatus permitting confining pressures up to 50 MPa and deviatoric straining of materials, while also allowing in situ x-ray measurements of grain-scale kinematics and stresses. Here, we present the design of and first results from HP-TACO during its use in laboratory and synchrotron settings to study grain-scale kinematics and stresses in triaxially compressed sands subjected to 15 and 30 MPa confining pressures. The data highlight the unique capabilities of HP-TACO for studying the high-pressure mechanics of sands, providing new insight into micromechanical processes occurring during geologic and man-made processes.

On the Mechanical Response of Aluminum Alloy 6061-T6 under Extreme Strains and Strain Rates, and Rapid Heating

The flow stress of aluminum alloy 6061-T6 produced by conventional thermomechanical methods has been investigated under the application of strains up to 80% at a strain rate of the order of 50001/s, and temperatures ranging from ambient to near melting. The high strain and strain rate deformation was imposed using a Kolsky bar compression apparatus equipped with a fast pulse-current heating system to reach the target temperatures at high heating rates. The flow stress was measured under strains, strain rates, temperatures and heating rates that match thermomechanical conditions developed in the primary shear zone of a specially designed machining with chip pulling test method. Flow stress error is estimated by statistics obtained from experimental replicates. It is expected that these measurements will enable the formulation of realistic machining models for Al6061-T6. Temperature measurements were obtained using non-contact infrared (IR) full field imaging together with embedded micro-thermocouple (TC) point probing. The TC measurements were used to estimate the emissivity of the aluminum specimen via separate, in situ calibration tests, and to track temperature evolution during the compression, also via separate testing, not compromising the flow stress measurements. Type-K TC measurements were made using the separated junction principle by embedding the TC wires into two micromachined holes in the specimen. The temperature measurement technique is discussed in detail, and temperature uncertainties are estimated. The Kolsky bar and machining test with chip pulling will be used going forward to study the effect of heating time on the dynamic thermal softening behavior of Al6061-T6, which has been shown to be time-sensitive under quasi-static loading when temperatures exceed 200°C, due to Mg-Si precipitate growth.

Large dynamic range, high resolution optical heterodyne readout for high velocity slip events.

We present a free-space optical displacement sensor for measuring geological slip event displacements within a laboratory setting. This sensor utilizes a fiberized Mach-Zehnder based optical heterodyne system coupled with a digital phase lock loop, providing a large dynamic range (multiple centimeters), high displacement resolution (with an amplitude spectral density of <10-10 m/Hz for frequencies above 100Hz), and high velocity tracking capabilities (up to 4.96m/s). This displacement sensor is used to increase the displacement and the time sensitivity for measuring laboratory-scale earthquakes induced in geological samples by using a triaxial compression apparatus. The sensor architecture provides an improved displacement and time resolution for the millisecond-duration slip events, at high containment and loading pressure and high temperatures. Alternatively, the sensor implementation can be used for other non-contact displacement readouts that required high velocity tracking with low noise and large dynamic range sensing. We use 13 high-velocity slip events in Fontainebleau sandstone to show the large dynamic range displacement tracking ability and displacement amplitude spectral densities to demonstrate the optical readout's unique sensing capabilities.

Solid stress impairs lymphocyte infiltration into lymph node metastases

Metastasis remains the principal cause of cancer mortality. Lymph node metastases are common and indicate poor overall prognosis, likely due to both the metastatic potential of primary tumor cells and the contribution of lymph node metastases to distant metastases. Although antitumor T cells are generated in lymph nodes, metastatic cancer cells are able to grow in this seemingly hostile microenvironment. We hypothesized that lymph node metastases actively suppress anti‐tumor responses in lymph nodes. The overall goal of our study is to understand how cancer cells avoid immune detection in lymph nodes. We obtained patient samples, established a novel ER+ mammary carcinoma (MCa) cell line and employed 4T1 triple negative breast cancer cells to investigate the growth of spontaneous lymphatic metastases. In addition, we developed a lymph node compression apparatus to mimic the compressive forces, known as solid stress, generated by cancer cells in lymph nodes. We used immunofluorescence microscopy, intravital imaging, flow cytometry, and quantitative PCR to characterize the effect of cancer growth on adaptive immune responses in tumor‐involved lymph nodes. Using patient tissue from multiple cancers and preclinical models of spontaneous lymph node metastases, we show that cancer cells disrupt lymphocyte trafficking to lymph nodes, resulting in exclusion of lymphocytes from metastatic lesions. The presence of solid stress caused by lesion growth is associated with a reduction of functional blood vessels and lymphocyte exclusion in the nodes. Relieving solid stress in the mice increased the presence of lymphocytes in lymph node lesions. These findings reveal a novel mechanism for the lack of immune response against lymph node metastases and may inform strategies for immunotherapy.

Intervertebral Disc Degeneration and Low Back Pain Depends on Duration and Magnitude of Axial Compression.

Purpose The pathological role of axial stress in intervertebral disc degeneration (IDD) is controversial, and there was no quantified study until now. Here, we tried to clarify the correlation between IDD or low back pain (LBP) and axial stress at different duration and magnitude in vitro and in vivo. Method In vitro, the gene expression of aggrecan, matrix metalloproteinase-3 (MMP3), calcitonin gene-related peptide (CGRP), and substance P (SP) was measured when nucleus pulposus cells (NPCs) were compressed under gradual severity. In vivo, a measurable Ilizarov-type compression apparatus was established for single coccygeal (Co) intervertebral disc (IVD) compression of Co7-8 in mouse. Gradient stress was placed at 0.4 Mpa (mild), 0.8 Mpa (moderate), and 1.2 Mpa (severe) for three days to investigate the effect of the magnitude of axial stress. Additionally, mild compression with 3, 7, and 14 days was used to determine the effect of the duration of axial stress. Subsequently, we evaluated the severity of IDD and LBP by radiological X-ray film; histological examination with H&E staining; immunohistochemical analysis with collagen II, aggrecan, and CGRP staining; and western blot analysis with collagen II, aggrecan, MMP-3, and interleukin-1β (IL-1β). Results When NPCs suffered gradual increased mechanical stress, the cells exhibited gradual downregulated expression of extracellular matrix (ECM)-related gene of aggrecan, upregulated expression of IDD-related gene of MMP3, and LBP-related gene of CGRP and SP. In the meantime, with different magnitudes of axial stress, the IVD showed progressively severe IDD and LBP, with gradual narrowing intervertebral height, destruction of IVD anatomy, decreased ECM, and increased catabolic factors and proalgesic peptides. Conclusion Axial compression is one of the critical pathological factors to cause IDD and LBP, and there was a strong positive correlation depended on the duration and magnitude of compression.

Measurement of Cement In-Situ Mechanical Properties with Consideration of Poroelasticity

Summary Accurate characterization of oilwell cement mechanical properties is key to establishing long-term wellbore integrity. The most widely used method is curing cement in an autoclave, demolding, cutting, and transferring it to a triaxial compression apparatus. The drawback of this traditional technique is that the mechanical properties are not measured under in-situ curing conditions. In this paper, we developed a high-pressure and high-temperature vessel to hydrate cement under downhole conditions and then directly measure cement Young’s modulus and Poisson’s ratio without cooling or depressurization. We validated the setup with water and obtained a reasonable bulk modulus of 2.37 GPa under elevated pressure. We proposed a poroelastic method to calculate cement elastic properties accounting for boundary stiffness and changing pore pressure. We compared the in-situ measurements with traditional triaxial compression tests conducted on the same specimen after retrieval from the vessel. The results show that in-situ measured Young’s modulus is more than double, and the Poisson’s ratio is 20 to 100% higher than that measured by the traditional triaxial method. One mechanism could be that the depressurization and repressurization process in those traditional tests may generate microdefects or induced stresses that weaken cement mechanical properties. Finally, we applied our mechanical properties measurements to cement wellbore integrity analysis by using a thermoporoelastic model. We found that the initial state of stress plays a significant role in maintaining wellbore integrity. With only mechanical properties differences considered, the estimation with traditional measured properties may mistakenly show cement is safe under some pressure and temperature perturbations.