Minimum Stress Research Articles

Surface topography assessment using chemical assisted ball end magnetorheological finishing

The generation of residual stresses by grinding process on the surface for a soft material result in poor performance and diminished life. Ball end magnetorheological finishing (BEMRF) process is a recently developed process that is effectively used for fine figuring and polishing of a variety of magnetic and non-magnetic materials. In this paper, grinding-induced residual stresses are addressed, and an attempt is made to relieve these residual stresses while achieving high surface finish using chemical assisted ball end magnetorheological finishing (CA-BEMRF) process. The chemical used in the present work is applied first time in BEMRF process and aluminium 7075 alloy workpiece has not been finished with this novel finishing process. The impact of various CA-BEMRF variables on percentage surface roughness reduction and percentage reduction in residual stresses are discussed statistically and graphically. Residual stresses of workpiece surfaces have been measured by using portable x-ray residual stress analyzer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) of the finished workpiece before and after CA-BEMRF process is carried out to assess the effects of magnetizing current, tool rotation and working gap on surface topography of machined surface. It has been observed that reduction in residual stress is achieved along with high surface finish on aluminium workpiece surface using CA-BEMRF technique. Significant process parameters affecting the residual stresses and surface roughness during polishing of workpiece are obtained using Analysis of variance (ANOVA) and F-test. The optimization problem for maximum percentage reduction in surface roughness and maximum percentage reduction in residual stress is formulated as multi objective, multi variable, nonlinear optimization problem. Maximum percentage surface roughness reduction and minimum residual stress has been found at magnetizing current 2.3 A, rotational speed of tool 550 rpm and working gap of 0.5 mm. Confirmatory experimental tests have been conducted and results obtained were found very close to the predicted outcome.

Multi-objective optimization of sandwich structures for reinforcing composite fuselages

This study introduces a simulation-based optimization approach that combines a multi-objective genetic algorithm and the finite element method to design sandwich structures to reinforce composite fuselages. The sandwich structure has been parametrized with a set of mixed integer-continuous variables representing the polymer core thickness, the number and weight of laminated fiberglass layers, and size and position of the structure. Automatic scripting builds the geometry of the structure, then mounts it in the fuselage, and finally creates a conformal mesh. During the optimization, each reinforced fuselage is subjected to several load cases specified by the CS-22 EASA design standard, determining the worst load condition. Two objectives were considered: increasing the reinforced fuselage’s minimum fiber stress safety factor for improved safety and reducing the number of layers of the sandwich structure to minimize manufacturing costs. Structural constraints were the mass of the sandwich structure and buckling and flexo-torsional deformation of the reinforced fuselage. Results show an efficient material arrangement due to the reduced number of layers in the sandwich structure and a stress safety factor surpassing that set by the standard. Finally, the reinforcement of a glider fuselage to incorporate a retractable electric propulsion system is presented as a real-world industrial application.

The influence of rheology in the fabrication of ceramic-based scaffold for bone tissue engineering

Abstract Bone tissue is the second most affected organ in the human body after blood. Tissue engineering is the area whereby a scaffold is used to regenerate the lost bone. However, the scaffold’s effectiveness is primarily based on the material and the fabrication process. The patient-specific structures are affected because of the fabrication process used to fabricate the scaffold as per requirement. In this regard, rheology plays an important role in the fabrication of the patient-specific scaffold, and it is a study of the flow of ink. This primarily affects both the conventional as well as the non-conventional fabrication processes. In this paper, the scaffold and bone tissue engineering, the different fabrication processes, and the importance of the rheological characterization are presented. In addition to this, the rheological properties of the developed HA/β-TCP composite slurry are evaluated for the extrusion-based additive manufacturing process. The developed ink’s rheological properties show that the flow behavior index of about 0.0497 ± 0.009, minimum flow stress required to make the ink flow of about 51.076 Pa at a strain rate of 0.111 %, and shape retention upto 75 % after 175 s are obtained. Also, different orientations are 3D printed using the developed slurry.

Mechanical parameter evolutions and deterioration constitutive model for ductile–brittle failure of surrounding rock in high-stress underground engineering

The deep surrounding rock is usually in the true triaxial stress state, and previous constitutive models based on the understanding of uniaxial and conventional triaxial test results have difficulty characterizing the degradation and fracture process of rock ductile–brittle failure under true triaxial stress state. Therefore, this study conducted a series of true triaxial tests to obtain the understanding of the ductile–brittle behaviour of rock, and then combined the test results and the Mogi–Coulomb strength criterion, and proposed calculation methods for the elastic modulus E, cohesion c and internal friction angle φ and the evolution functions of E, c and φ of rock under true triaxial stresses. With the decreasing of the minimum principal stress σ3 or increasing of the intermediate principal stress σ2, the marble post-peak stress drop rate gradually increases, the ductility gradually weakens, and the brittleness significantly strengthens. The calculation method and evolution function of rock E, c and φ under true triaxial stress were proposed. E decreased at first and then tended to remain stable with the increasing of equivalent plastic strain increment dεp. c and φ slowly increased at first and then rapidly decreased. With a method of parameter degradation rate to realize post-peak stress drop rate to reflect the ductile–brittle characteristics, a new three-dimensional ductile–brittle deterioration mechanical model (3DBDM) was established. The proposed model can accurately characterize the influence of σ2 and σ3 on mechanical parameters, the ductile–brittle behaviour of rock under true triaxial stresses, and the asymmetric failure characteristics of surrounding rock after excavation of deep underground engineering. The proposed model can be reduced to elastic–perfectly plastic, elastic–brittle, cohesion weakening friction strengthening (CWFS), Mohr–Coulomb, and Drucker–Prager models.

Machine learning and DFT-based combined framework for predicting transmission spectra of quantum-confined bio-molecular nanotube.

The Adenine-based nanotube is theoretically designed, and its transmission spectra are investigated. The quantum-confined Adenine nanotube shows electronic transmission of the carrier at minimum stress. In this paper, the prediction of transmission spectra of the quantum-confined bio-molecular nanotube is investigated and deeply studied. Molecular level structure prediction and their electronic characterization can be possible with ab initio accuracy using a machine learning algorithmic approach. At the molecular level, it is difficult to predict quantum transmission spectra as these results are always hampered by the carrier backscattering effect. However, mostly these predictive models are available for intrinsic semi-conducting materials and other inorganic structures. Machine learning algorithms are designed to predict the electronic properties of the nano-scale structure. This task is even more difficult when quantum-confined molecular arrangements are considered, whose transmission spectra are sensitive to the confinements applied. This paper presents an effective machine learning algorithms framework for predicting transmission spectra of quantum-confined nanotubes from their geometries. In this paper, we consider regression machine learning algorithms to find maximum accuracy with varying configurations and geometries to excerpt their atoms' local environment information. The Hamiltonian components are then used to enable the utilization of the information to predict the electronic structure at any arbitrary sampling point or k-point. The theoretical basics introduced in this process help to capture and incorporate minor changes in quantum confinements into transmission spectra and provide the framework algorithm with more accuracy. This paper shows the ability to predict the accurate algorithmic models of the Adenine nanotube. In this framework, we have considered a tiny data set to achieve a rapid and reliable method for electronic structure determination and also propose the best algorithm for predictive model analysis.

Correlation between reliability and safety factor based methods in characterizing uncertainty of creep rupture properties

Reliability and safety factor based methods are usually employed to characterize uncertainty of creep rupture properties, but the correlation between these two methods is rarely reported. In this work, a framework of correlation between reliability and safety factor based methods was proposed, and application of this framework in representation of minimum stress to creep rupture was reported. Effect of standard deviation on correlation results was discussed and comparisons of minimum stress to creep rupture in codes and standards were conducted. Results indicated that for a given reliability, the safety factor included in the minimum stress to creep rupture is higher at a small stress level and a high temperature. Accordingly, the minimum stress to creep rupture by reliability based method in ASME code (i.e. 95 %) is lower than that by safety factor based method in RCC-MRx code (i.e. 1.25), presenting a smaller allowable stress value and more conservative evaluation. Contrarily, a smaller safety factor is gained at a high stress level and a low temperature for a given reliability. The opposite conclusion is drawn when the reliability at a given safety factor is analyzed. In addition, the safety factor of 1.5 is larger than that at the reliability of 99 % for a wide range of stress levels, inducing an over-conservative design and excessive manufacturing costs.

Modifying the orientation of hydraulically fractured wells in tight reservoirs: The effect of in-situ stresses and natural fracture toughness

Hydraulic fracturing in shale formations containing natural fractures can lead to complex and branched fracture networks which may fail to efficiently access hydrocarbons deep in the formation away from the well. In this study, to minimise the negative effects of natural fractures, the orientation of hydraulically fractured wells in such formations is investigated with the focus on the effects of in-situ differential stresses and toughness of natural fractures. To explore the impact of geomechanical properties on gas production from hydraulically fractured wells, fractures were first up scaled and then gas production from the reservoir was investigated. The results show that low natural fracture toughness and differential in-situ stress both increase the tendency of propagating hydraulic fractures to exploit natural fractures. Under these conditions, it was found that drilling the well in a modified orientation could result in a higher recovery factor compared to the wells drilled parallel to the direction of minimum horizontal stress. This is due to the larger stimulated reservoir volume through a synergy between the hydraulic and natural fractures. However, high differential in-situ stress and fracture toughness both lead to a transition from this tendency, in which hydraulic fractures cross natural fractures rather than exploiting them. As a result, changing the well orientation in these scenarios are less efficient than the industry standard. The results of this study demonstrate a window of geomechanical scenarios in which changing well orientation is beneficial, can be produced as a fast-screening method for engineers to determine the optimised well orientation.

Pavement Condition Index Model for Mechanistic–Empirical Design of Airport Concrete Pavements Considering Environmental Effects

A transfer function is the main model of a design program that correlates mechanistically calculated damage to a pavement with the actual field distress. In this study, a pavement condition index (PCI) model that reflects environmental and traffic loads was developed as a transfer function for a design program for airport concrete pavements. Seven runways from five airports in Korea, for which design data were available, were selected as target runways, and their design, traffic, and weather data were collected. The minimum tensile stress of the slab generated by environmental loads and the maximum tensile stress induced by combined environmental and traffic loads were calculated by conducting a three-dimensional finite element analysis. The cumulative fatigue damage to the target runways was calculated by substituting the climatic conditions and traffic volume into the fatigue model, which considered the minimum and maximum tensile stresses. The PCI, which was uniformly and varyingly distributed according to pavement age, was adopted as the indicator of actual field distress, whereas the previously used structural condition index was mostly 100 because no structural distress occurred, regardless of the pavement age. The PCI model was established via multi-regression analysis to predict field PCIs using mechanistically calculated cumulative fatigue damage and pavement age as independent variables. The actual and predicted PCIs of the target airports were compared to validate the PCI model.

Experimental Studies on the Crack Initiation and Propagation of Hydraulic Fracturing with Different Coal Structure Combinations.

Coal structure is one of the key geological factors that affects the effect of coal reservoir stimulation. Based on the geological spatial combination characteristics, thickness, and proportion of different coal structures, the coal reservoir is divided into different coal structure combination types. The hydraulic fracturing device is used to carry out indoor fracturing experiments and dissect the crack initiation and expansion characteristics with different coal structure combinations. The results show that the coal structure combination is of the binary type (undeformed coal + granulated coal or cataclastic coal + granulated coal), and the undeformed coal (cataclastic coal) can overcome the tensile strength and minimum principal stress when it is driven by the high-pressure fluid. The undeformed coal (cataclastic coal) ruptures and forms longitudinal cracks. The increasing proportion of granulated coal inhibits crack expansion and promotes the transverse deformation of coal. The interface contact point between the undeformed coal (cataclastic coal) and granulated coal easily fractures along the cross section of the specimen. When the coal structure combination is the triplex type (undeformed coal + granulated coal + cataclastic coal or cataclastic coal + granulated coal + cataclastic coal), the undeformed coal or cataclastic coal is transformed. The forming fractures in the undeformed coal (cataclastic coal) can cut through the soft coal when the thickness of the undeformed coal (cataclastic coal) is large and the thickness of granulated coal is thin. On the contrary, it is not easy to cut through. When the coal structure combination is granulated coal + cataclastic coal + granulated coal, the cataclastic coal fails under shear stress and forms the crack along the cross section of the coal sample. The granulated coal inhibits the crack expansion at both ends. The research results have an important indicative significance for further understanding the fracture initiation and propagation mechanism of hydraulic fracturing with complex coal structures in coal reservoirs.

Multi-scale model to study gas transport processes in clay materials

In the field of radioactive waste confinement, the question of gas transfers in clay formations is a crucial issue [1]. A certain amount of gas, such as Hydrogen may be generated during the exploitation phase in the nearfield by the deterioration of the metal components of the system. Since the host medium is characterised by a very low permeability, the mechanisms of gas transport by advection and diffusion within the groundwater remain insufficient to evacuate the gas generated and a free gas phase is formed. If the gas pressure keeps increasing and reaches the minimum principal stress acting on the rock, micro-fractures, known as preferential gas pathways could develop through the rock mass [2], and affect the clay barrier integrity.
 There is a growing body of experimental evidences [3, 4] that separation planes such as bedding planes or pre-existing fractures and heterogeneities in clay-rich materials represent preferred weaknesses for the process of opening discrete gas-filled pathways. Capturing the related transport mechanisms therefore requires to go from macroscopic to microscopic scale. In this context, the adopted numerical approach would ideally take into account the effect of each constituent of the material microstructure on the macroscopic gas flow. Yet, direct modelling of the entire microstructure using small-scale models is usually not possible due to the huge computational costs it would require at the scale of a repository. Conversely, indirect modelling of the behaviour of all the micro-constituents by collective closed-form macroscopic constitutive equations using large-scale models [5] has also limits in terms of assumptions formulation and parameters identification. Hence, the use of a multi-scale approach that models the micro-scale effects explicitely on their specific length scale and couples their homogenized effects to the macro-scale is proposed in the present work. Based on a periodicity assumption of the microstructure, the physical and geometrical properties of the microstructure are embedded on a Representative Element Volume (REV) which contains a detailed model of the microstructure constituents, i.e. the pore network, the bedding planes and the bridging planes, while eluding a complex description of the whole microstructure over the domain. From this local description of the material, the macroscopic response to loading can be derived using numerical homogenisation techniques [6].
 The multi-scale model proposed here has been implemented in the finite element code Lagamine, and validated against a well established and documented macro-scale THM coupled model [7]. The size and structure of the REV comes from experimental data acquired from scanning images in clay material, like for instance the Boom Clay formation which is envisaged as a potential host rock for a deep geological disposal in Belgium. Such scans reveal the opening of large aperture with a repeated distance in-between, which make it possible to extrapolate a physical idealisation of the microstructure (Figure 1a), built with one of these fractures corresponding to the bedding planes (red) and the pore network substituted by an assembly of tubes (green). Narrow-aperture fissures, known as the bridging planes (blue) were also identified to contribute to the flow normal to the predominant direction of fissure [4], by connecting the natural discontinuities which were initially closed. These micro-scale constituents are defined in such a way as to satisfy the conditions of pore size distribution, macroporosity and intrinsic permeability. For the mechanical behaviour, a simple linear elastic constitutive law was introduced for the tube network while a non-linear stress-strain relationship was used for the interfaces defining the bedding and bridging planes. Concerning the hydraulic behaviour, gas diffusive fluxes were considered and modelled by a Fick’s law while a channel flow based on the Navier-Stokes equations was used for the multiphase flow in the different constituents.
 The model has been subsequently applied to simulate a gas injection test parallel and perpendicular to the bedding of initially saturated samples of Boom Clay [4]. This analysis provides a rather good agreement with the experimental results in terms of injection and outflow pressure response, outflow volume and average axial strain along the sample height. In addition, it allows to simulated the creation of a preferential flow pathway along the sample axis (Figure 1b, top), which serves as basis to numerically reproduce the development of random pathway through the sample in plane strain state (Figure 1b, bottom), and aims to improve the mechanistic understanding of the gas transport processes at play in clayey barriers [8].

Biomechanical Fixation Analysis of Minimally Invasive Chevron Osteotomy

Category: Bunion Introduction/Purpose: The original fixation for minimally invasive Chevron-Akin ( MICA) was described with two screws: a proximal screw reaching two cortices before fixing the metatarsal head and a distal parallel screw that can reach only one cortical before fixing the head. Despite this, some authors questioned the need for two screws and were able to reproduce good results from this technique using only one screw to fix the osteotomy. Notably, no biomechanical studies evaluate this osteotomy's most stable and safe fixation. This work aims to perform a biomechanical analysis based on finite element analysis (FEM) to compare different MICA fixation configurations using screws. Our hypothesis is that the fixation of the original technique with two screws is the safest. Methods: A Three-dimensional (3D) virtual model of a foot computer tomography (CT) image was made using the Rhinoceros™ program. The element finite analysis was performed with the SimLab™ program using the Optistruct solver. From these 3D virtual models, an extracapsular chevron osteotomy with 130 degrees with 70% of lateral translation was done and fixated. Five internal fixation configurations with screws were used for fixation of MICA and assessed by FEM -: original MICA fixation with 2 screws, 2 intramedullary screws, 2 bicortical screws, 01 intramedullary screw, and 01 bicortical screw. The simulated 150 N and 300 N loads were applied to the middle foot. The FEM evaluated the total and localized displacements of the osteotomy site. For the analysis of stresses, the variables maximum principal (traction) and minimum principal (compression) were used. The equivalent von Mises stress (VMS -S) was used for the metallic implants and for the bone (VMS -O). Results: The classical fixation for MICA showed the lowest values for total and localized displacement, minimum and maximum total stress, and VMS-S and VMS-o in both conditions( 150 and 300 N). The localized displacement was statistically lower for MICA screws compared to the other fixation configurations (p < 0.05) The maximum total stress was statistically lower for MICA screws compared to the other fixation configurations (p < 0.05) Conclusion: The classical fixation for MICA yields better results in terms of total and localized displacement, minimum and maximum total stress, and VMS in both conditions. These results demonstrate that the classical fixation for MICA described in the original technique is biomechanically the most efficient and safe.

Biomechanical behavior of carbon fiber-reinforced polyetheretherketone as a dental implant material in implant-supported overdenture under mandibular trauma: A finite element analysis study.

Implant-supported overdentures are well-known and widely accepted treatment modality to increase retention which is a crucial factor for determining patient satisfaction. The placement of two implants in the anterior region can be selected as a first-line treatment in patients with the atrophic mandibular ridge. The purpose of this research was to assess the biomechanical effects of carbon fiber-reinforced polyetheretherketone (CFR-PEEK) implant-supported overdenture in the event of 2,000 N forefront trauma to an atrophic edentulous mandible by using the finite element analysis method. Three types of mandible models were simulated; the first one was an edentulous atrophic mandible model; in the second model, 3.5 × 11.5 mm CFR-PEEK implants; and in the third model, 4.3 × 11.5 mm CFR-PEEK implants were positioned in the region of the lateral incisor of the identical edentulous atrophic mandible. Maximum Von Misses stresses 979.261 MPa, 1,454.69 MPa, and 1,940.71 MPa and maximum principal stresses 1,112.74 MPa, 1,249.88 MPa, and 1,251.33 MPa have been detected at the condylar neck area and minimum principal stresses - 1,203.38 MPa, -1,503.21 MPa, and - 1,990.34 MPa have been recorded at the symphysis and corpus regions from M1 to M3, respectively. In addition, the M2 and M3 models showed low-stress distributions around the implant-bone interface, particularly where the implants were in contact with cancellous bone. The results showed that the insertion of different diameters of CFR-PEEK implants led to low and homogenous stress distribution all around the implant-bone interface and stresses transferred directly to the condylar neck areas. Therefore, it was observed that CRF-PEEK implants did not change the basic behavior of the mandibula in response to frontal stresses.

Using One-Dimensional Geomechanical Model for Determining the Safe Wellbore Orientation of Zubair Reservoir, Southern Iraq

The wellbore instability issues are firmly occurring in the Iraqi oilfield and particularly in the southern region of Iraq. It is causing a significant loss of time dealing with many types of downhole problems, as well as an increase in the operations costs because of the instability consequences. By using the well information and open-hole logging data, the One-Dimensional (1-D) geomechanical model generated with Schlumberger Techlog software (V.2015) was used to assess the mechanical stability of the wellbore. The model was calibrated and validated by using core data (Triaxial test), the formation pore pressures, and the Mini-frac test). The 1-D model was validated across the actual well conditions (i.e., the original mud weight and the actual wellbore failure) by using three criteria of failures which are Modified Lade, Mogi-Coulomb, and Mohr-Coulomb. The validation process showed that the failure criterion of Mogi-Coulomb is better than the other two criteria in presenting the actual borehole failure, and thus it can be used to develop the plans of wellbore orientation. By investigating wellbore orientation with various scenarios, ranging from a vertical trajectory to the horizontal strategy, the wellbore orientation is mainly safe (with the minimum breakout) in vertical and inclined wells up to 40º with minimum mud weight of 11.7 and 12.6 ppg. The optimum wellbore trajectory should be in the direction of minimum horizontal stress, which is North-West to South-East (130º-160º). The developed plans provide a guideline for performing stable drilling operations in the south of Iraq and the nearby areas, thus effectively contributing in reduction the overall cost.

Design and Frame Strength Evaluation of Salt Washing Unit Capacity 50 Kg/hour

The salt washing unit is part of the salt processing machine. This unit's function is to wash raw salt with brine. This unit has a motor, agitator blade, washing chamber, and frame. The frame structure strength of the salt washing unit needs to be evaluated to ensure safety. This research aims to design the salt washing unit and obtain simulation results of frame structure strength to ensure the safety of the salt washing unit. This research was carried out by simulation to look for stress, strain, and changes in the shape of objects (displacement). The frame strength simulation was carried out using Solidwork software. The salt washing unit with a 50 kg/hour capacity has been designed. It has a cylindrical shape with 990 mm in height and 680 mm in diameter. From the simulation results of strain, it can be concluded that the minimum point is 1.80 × 108 Mpa, and the maximum point is 1.63 × 105 Mpa. From the simulation results of displacement, it can be concluded that the minimum point is 0 mm and the maximum point is 2,296 mm. The maximum stress is 5.254×106 N/m2, and the minimum stress point is 1.803×106 N/m2.

Prediction of formation pressure based on numerical simulation of in-situ stress field: a case study of the Longmaxi formation shale in the Nanchuan area, eastern Chongqing, China

The in-situ stress and formation pressure are important parameters in shale gas development. They directly affect the well wall stability, the direction of horizontal well drilling, and the fracturing effect during the shale gas development process. There are abundant shale gas resources in the southeastern Chongqing-Sichuan area, but the structure in the area is complex, and it is difficult to predict the in-situ stress and formation pressure. Therefore, in this paper, a finite element simulation model was established based on a large number of seismic, logging, and experimental rock mechanics data and the prediction accuracy of the stress field simulation was effectively improved. The construction of the stress field was based on the combined spring model, as well as the data related to the measured in-situ stress and the formation pressure obtained during drilling. The coupling relationship between the in-situ stress, the formation strain, and the formation pressure were derived to carry out the prediction of the distributions of the formation pressure and the formation pressure coefficient. The prediction results showed that the present-day maximum principal stress direction in the study area was about NE65°–110°, and the present-day maximum principal stress was 56.12–93.79 MPa. The present-day minimum principal stress direction was about NE335°–20°, and the present-day minimum principal stress was 48.06–71.67 MPa. The formation pressure was 2.8–88.25 MPa, and the formation pressure coefficient was 0.74–1.55. The formation pressure distribution was greatly affected by fault, tectonic location, in-situ stress and rock petrophysical properties, and the overpressure areas of the formation were distributed in the synclines and the deeply buried areas. This study shows that the finite element based formation pressure prediction method is effective.

Stress Constraints From Shear‐Wave Analysis in Shallow Sediments at an Actively Seeping Pockmark on the W‐Svalbard Margin

AbstractMechanisms related to sub‐seabed fluid flow processes are complex and inadequately understood. Petrophysical properties, availability of gases, topography, stress directions, and various geological parameters determine the location and intensity of leakage which change over time. From tens of seafloor pockmarks mapped along Vestnesa Ridge on the west‐Svalbard margin, only six show persistent present‐day seepage activity in sonar data. To investigate the causes of such restricted gas seepage, we conducted a study of anisotropy within the conduit feeding one of these active pockmarks (i.e., Lunde Pockmark). Lunde is ∼400–500 m in diameter, and atop a ∼300–400 m wide seismic chimney structure. We study seismic anisotropy using converted S‐wave data from 22 ocean‐bottom seismometers (OBSs) located in and around the pockmark. We investigate differences in symmetry plane directions in anisotropic media using null energy symmetries in transverse components. Subsurface stress distribution affects fault/fracture orientations and seismic anisotropy, and we use S‐wave and high‐resolution 3D seismic data to infer stress regimes in and around the active seep site and study the effect of stresses on seepage. We observe the occurrence of changes in dominant fault/fracture and horizontal stress orientations in and around Lunde Pockmark and conclude minimum (NE‐SW) and maximum (SE‐NW) horizontal stress directions. Our analysis indicates a potential correlation between hydrofractures and horizontal stresses, with up to a ∼32% higher probability of alignment of hydrofractures and faults perpendicular to the inferred minimum horizontal stress direction beneath the Lunde Pockmark area.

Combined loading performance analysis of gasketed bolted flange joints with emphasis on bolt scattering

Gasketed bolted flange joints (GBFJ) are commonly used in various industries however, their failure could result in significant losses not only in terms of financial but human life as well. Most of the work present on the performance of the GBFJ involves simplified assumptions by neglecting the effect of bolt scatter. Also, there is a paucity of studies investigating the sealing performance of GBFJ under combined thermal transient and structural loading. In the present study, two different flange sizes of ANSI B16.5 pressure class 900 (4in. and 6in.) are evaluated, using a detailed three-dimensional finite element analysis (FEA). ASME bolt tightening scheme was applied for the preloading of the bolts. Higher bolts and gasket stresses were observed in the case of 6in. flange joint. Also, greater variation in bolt stresses (up to 18 % of the target value) was observed for the 6 in. model which may be due to higher number of bolts resulting in greater scattering phenomena. Both models were found to be safe under the structural loading. However, large relaxation in stresses was observed at high bulk temperature. The gasket stress in 4in. flange model was observed to be less than the minimum seating stress (69 MPa) at temperatures greater than 300 °C implying possible leakage. However, stresses in the 6in. model stayed within the safe limit throughout the thermal and structural loading due to higher bolt target stresses, resulting in its proper seating even at higher temperatures.

Casting and installation of segmental precast quadratic concrete driven geothermal energy piles

Geothermal energy pile foundations are used both for structural purposes and to provide sustainable, clean, and cost-effective ground energy for heating and cooling buildings [1]. The majority of energy piles are cast-in-place concrete piles, which require extensive and expensive drilling during construction. A better alternative is to use precast concrete segmental driven energy piles, which can be cast in large quantities with high-quality assurance at a concrete factory, after which they are transported and installed into the ground [2]. This study aims to present a novel method of casting and installing segmental energy piles that utilize an innovative steel joint [3] for connecting the precast concrete segments on-site. In addition to structural integrity, the steel joint provides the possibility of a leak-proof coupling and continuity for heat-exchanging pipes embedded in concrete segments. The precast-driven pile foundations are made of high-strength concrete with a 14-day compressive strength of almost 80 MPa and have a quadratic shape with a maximum length of 12 m and a square width of 270 mm or 350 mm. In the 270-mm piles, a single U-loop can be used, while in the 350-mm piles, two U-loops can be used as presented in Figure 1. The heat-exchanging pipes are coupled inside the sidewall channels of the steel joint which are shielded using a steel cover plate, riveted to the joint. At the tip of the bottom segment of the piles, there is a strong steel rock shoe with a hardened steel point that allows the piles to penetrate the bedrock [4]. At a construction site, the joint and pipes can be connected quickly without any welding or electric equipment that expedites the installation work and obsoletes the health and safety risk associated with electricity. Utilizing the precast energy piles presented in this study increases the quality, and speed of installation while decreasing the overall cost of the project compared to cast-in-place energy piles. To prove the proper performance of the piles under real construction conditions, structural integrity tests and hydraulic pressure tests were performed according to BS EN 12794:2005 [5] and ASTM F2164–21 [6], and the results are briefly presented and discussed in the present study. Structural integrity tests consisted of impact tests in which 1000 blows imposing a minimum stress level of 28 MPa were applied on the pile segments connected using the new driven energy pile joint. During the impact tests, the pile structure and the joints remained undamaged. After the impact tests, the pipes were pressurized up to 100 psi (690 kPa) and no leakage or pressure drop was observed. Then the pile segments were cut according to the standard into shorter segments and subsequent bending tests were performed to measure the bending capacity. The bending tests show that the driven energy pile joints have a similar bending capacity as conventional normal joints. The results of this study show that segmental precast concrete energy piles using the new steel driven energy pile joints, are a perfect alternative for cast-in-place energy piles, which can provide sufficient structural and bearing capacity and can be used both for heating and cooling buildings.

Optimum design of a composite drone component using slime mold algorithm

Abstract Composite materials have a wide range of applications in many industries due to their manufacturability, high strength values, and light filling. The sector where composite materials are mostly used is the aviation industry. Today, as a result of the development of aviation systems, drones have started to be actively used, and many studies have started to be carried out to mitigate them. In this study, the subcarrier part, which is part of the drone, was designed using glass and carbon fiber–reinforced composite materials. Using the data obtained at the end of the analysis, the stacking angle with the optimal displacement and stress value was determined by using the genetic algorithm (GA), gray wolf algorithm (GWO), and slime mold optimization (SMO) techniques in order to develop a carrier with a minimum displacement and stress value of more than 60 MPa. As a result of the optimization, it was determined that artificial intelligence algorithms could be used effectively in determining the stacking angle of composite materials, and the optimum values were determined in the slime mold algorithm.

True triaxial stresses mobilizing dilatant fracturing and engineering failure of hard rocks

Rock dilation represents a nonlinear deformation and volume change, which can be quantified by the dilation angle, and plays a crucial role in the failure analysis of underground engineering. Traditionally, triaxial models describe the dilation angle as a function of confining stress and plastic shear strain. However, this study has uncovered a new mechanism governing true triaxial compressive fracturing, where dilatant fracturing is naturally mobilized by true triaxial stresses and significantly influenced by intermediate principal stress. The dilation angle has been observed to rapidly increase to a peak and then gradually decrease to a small value with increasing plastic shear strain. Additionally, as the minimum and intermediate principal stresses increase, the rate of change and peak value of the dilation angle decrease. Conversely, these features are reversed when the intermediate principal stress approaches or exceeds the uniaxial compressive strength of hard rocks. In light of these discoveries, based on previous research, a novel rock dilation angle (RDA) model is proposed to describe rock dilation behavior under true triaxial compression, where true triaxial stresses mobilize the dilation angle. The findings and proposed model demonstrate the true triaxial stress-dependent dilatancy behaviors in hard rocks, which are of significant importance for failure analysis in deep rock engineering.