Loading Direction Research Articles

Development of a Cone Penetration Testing Apparatus with a Textured Shaft

The anisotropy of shear resistance depending on friction direction can be selectively utilized in geotechnical structures. For instance, deep foundations and soil nailing, which are subject to axial loads, benefit from increased load transfer due to greater shear resistance. In contrast, minimal shear resistance is desirable in applications such as pile driving and soil sampling. Previous studies explored the shear resistance by interface between soil and surface asperities of a plate inspired by the geometry of snake scales. In this study, the interface friction anisotropy based on the load direction of cones with surface asperities is evaluated. First, a laboratory model chamber and a small-scale cone system are developed to quantitatively assess shear resistance under two load directions (penetration ⟶ pull-out). A preliminary test is conducted to analyze the boundary effects for the size of the model chamber and the distance between cones by confirming similar penetration resistance values at four cone penetration points. The interface shear behavior between the cone surface and the surrounding sand is quantitatively analyzed using cones with various asperity geometries under constant vertical stress. The results show that penetration resistance and pull-out resistance are increased with a higher height, shorter length of asperity and shearing direction with a decreasing height of surface asperity.

Microstructural Evolution and Mechanical Properties of Reeled X65 Pipeline Steel during Cyclic Plastic Deformation and Natural Aging

The reel laying is recognized as a cost‐effective installation process for offshore pipelines. However, the mechanical properties are modified due to plastic deformation during the reel laying and lowering process of reeled pipelines and the subsequent natural aging in service. Cyclic plastic deformation (CPD) is conducted on X65 pipeline steel to simulate the strain experienced in the reel‐laying and lowering process, and then, the CPD specimen is aged at 250 °C to simulate natural aging in service. The dislocation configurations gradually evolve from dislocation lines and tangles into dislocation walls and cells due to the increase in strain level. After CPD and aging, the tensile strength increases by about 25 MPa, which is not significantly affected by the last introduced load direction and strain level. At the end of compressive loading, the yield strength and yield ratio decrease, but the uniform elongation increases significantly. In contrast, at the end of tensile loading, the yield strength and yield ratio increase, but the uniform elongation decreases slightly. The yield strength further increases as the strain level increases from 2 to 3%. Therefore, CPD and aging modify the mechanical properties of X65, considerably depending on the last introduced load direction and strain level.

Hybrid Testing System Development for Single Point Mooring Lines FOWT’s

Abstract To advance the development of various concepts for floating offshore wind turbines, it is imperative to have access to experimental data. These data are used in the validation of the tools for the simulation of floating turbines and also for the tuning of the models. CENER has developed a hybrid testing methodology that enhances the performance of wave basin tests for scaled models of Floating Offshore Wind Turbines (FOWTs). This approach allows us to apply forces and moments from the wind turbine to the floating platform without needing to replicate wind within the testing facility or create a complex model of the wind turbine rotor. However, when it comes to testing single point moored (SPM) platforms, a unique challenge arises. These platforms have an additional degree of freedom as they can freely rotate around the vertical axis of their mooring attachment (yaw degree of freedom). These type of platforms can present important misalignments with respect to the wind depending on the combination of wind, wave and current directions. Consequently, accurately capturing the impact of misalignment on platform dynamics, especially in yaw, is essential to assess the platform’s ability to self-align with the wind direction, a key factor known as weathervaning capacity. The X1Wind platform is an innovative floating wind system, based on a single point mooring solution with a downwind wind turbine configuration that allows it to be passively self-orientated. The concept has been extensively tested on prototypes at real sea conditions as well as on scaled models at wave basins. For the last wave basin testing campaign, X1Wind has entrusted CENER with the development of the hybrid testing methodology adapted to the requirements of SPM platforms. The testing campaign has covered different wave and wind conditions, including misalignment scenarios and has shown a good dynamic behavior of the platform on yaw. This study outlines the advancements made in the CENER Software-in-the-Loop (SiL) hybrid testing system for wave basin tests of SPM platforms. In order to correctly introduce the direction of the aerodynamic forces on the wind turbine under misaligned conditions, improvements on the software and hardware (loads actuator) of the SiL system were developed and tested. An actuator system consisting of 6 propellers was used. The numerical model that calculates the rotor aerodynamic loading were expanded to take into consideration the direction of the aerodynamic loads with respect to the platform. Additionally, the drag of the wind over the tower and other platform elements must be considered, as they can play a relevant role in the generation of the weathervaning moment. The study concludes that the use of the upgraded SiL hybrid testing system is an effective and afordable solution for the testing of scaled SPM platforms at wave basin facilities. It also summarizes the different considerations that the system has to overcome for the particularity of this type of testing application.

Influence of Loading Direction on Compressive Strength of Concrete Block Masonry

Influence of Loading Direction on Compressive Strength of Concrete Block Masonry

Role of inclusion clusters on fatigue crack initiation in powder metallurgy nickel-based FGH96 superalloy

Inclusion clusters with a size of several tens of micrometers were found to be inclined to early crack initiation, resulting in an abnormally reduced fatigue life. Fatigue tests were conducted to elucidate crack initiation behaviors of inclusion clusters in nickel-based powder metallurgy (P/M) FGH96 superalloy. The inclusion clusters with varying sizes and shapes located at grain boundaries are composed of Al2O3, MgO and ZrO2 particles. The inclusion cluster with large size within 25-35 μm, small average particle distance within 0-4 μm and large orientation relative to loading direction within 35-66° will be more likely to cause crack initiation. In particular, the inclusion clusters with large size and high aggregation degree experience extruding during processing and subsequent heat-treatments due to the difference in thermal expansion coefficient with the matrix behave multiple cracking before fatigue loading, thereby facilitating crack initiation in the surrounding matrix grains. Moreover, as the main cracking part of inclusion clusters, the Al2O3 particles exhibit self-cracking and interface debonding, owing to higher hardness and poorer deformation coordination degree with matrix compared to other component inclusion particles.

Individual differences in acceptance of direct load control

Individual differences in acceptance of direct load control

Influence of Strain Rate on Barkhausen Noise in Trip Steel

This paper deals with Barkhausen noise in Trip steel RAK 40/70+Z1000MBO subjected to uniaxial plastic straining under variable strain rates. Barkhausen noise is investigated especially with respect to microstructure alterations expressed in terms of phase composition and dislocation density. The effects of sample heating and the corresponding Taylor–Quinney coefficient are considered as well. Barkhausen noise of the tensile test is measured in situ as well as after unloading of the samples. In this way, the contribution of external and residual stresses on Barkhausen noise can be distinguished in the direction of tensile loading, as well as in the transversal direction. It was found that the in situ-measured Barkhausen noise grows in both directions as a result of tensile stresses and the realignment of domain walls. The post situ-measured Barkhausen noise drops down in the direction of tensile load due to the high opposition of dislocation density at the expense of the growing transversal direction due to the prevailing effect of the realignment of domain walls. The temperature of the sample remarkably grows along with the increasing strain rate which corresponds with the increasing Taylor–Quinney coefficient. However, this effect plays only a minor role, and the density of the lattice imperfection expressed especially in terms of dislocation density prevails.

Behaviour of paddled energy-absorbing rockbolts under complex loading laboratory conditions

Since their introduction in 2010, paddled energy-absorbing rockbolts have been widely used in seismically active hard rock mines. This paper provides new data and reviews previous work to quantify the performance of paddled energy-absorbing rockbolts under controlled laboratory conditions. Of significance is the realization that the typical split location in impact tests, at the centre between two paddle anchor points can at best provide an upper limit value. This inherent variability in performance under different testing configurations should be acknowledged and taken into consideration in the design of ground support in seismic conditions. This paper discusses the reduction in capacity of paddled rockbolts as a function of loading angle from a maximum value during axial tests (0° loading angle) to the lowest value during pure shear (loading angle of 90°). A significant reduction in displacement capacity is observed as the loading angle changes between axial (0°) and 40°. Beyond a 40° loading angle up to shear (90°) loading the reduction in displacement capacity is less significant. Due to the variances in the capacity observed through the variance of the testing configuration: loading mechanism, direction of loading, location / presence of a discontinuity, it must be recognized that results from laboratory-based testing are not independent of the testing configuration. This should be acknowledged when extrapolating anticipated performance in the field.

Crack Propagation Tests for Load Sequences Developed Using Different Flight Parameters of a Trainer Aircraft

Abstract Military aircraft are subjected to highly variable and unpredictable loads due to diverse mission profiles, armament configurations, and individual piloting styles. This variability complicates the definition of precise load spectra, particularly in cases where data loss occurs due to Flight Data Recorder (FDR) malfunctions or data mishandling. This paper investigates the use of different flight parameters, such as load factor (nz ), barometric height (Hb ), and horizontal velocity (Vp ), to define load sequences for the PZL-130 “Orlik” TC-II military trainer aircraft. These sequences were then used to evaluate crack propagation using Compact Tension (CT) specimens. The results show that the incorporation of additional flight parameters improves the accuracy of crack propagation predictions when compared to direct strain measurements. This study highlights the potential of using available flight data to develop reliable load spectra for fatigue life estimation in military aircraft, even when direct load measurements are not financially feasible.

Fracture Analysis of 316L Specimens Fabricated via Material Extrusion Additive Manufacturing: Influence of Building Orientation and Notch Acuity

ABSTRACTThree‐point bending tests were performed on notched specimens extracted from cuboids of 316L stainless steel produced via material extrusion additive manufacturing. The cuboids were printed vertically and horizontally on the printing platform to account for the building orientation effect on the mechanical performance. For each orientation, three notch sizes were considered. Overall, the specimens printed with building direction parallel to the loading direction outperformed the others. A significant notch size effect was observed in these specimens since the sharpest notch provoked a decrease in the peak load reached by the specimens in comparison with larger notches. On the contrary, this effect was less relevant among the other specimens, which presented a conspicuous amount of residual porosity that contributed to the premature failure. Further investigations were carried out to correlate the building orientation to the density of the parts and, ultimately, to the investigated mechanical properties. The ASED and TCD criteria were also applied to assess their accuracy in the failure prediction of the tested specimens.

A new three-dimensional strength criterion considering the transverse isotropy based on the α-Spatial Mobilized Plane

Natural geotechnical materials are affected by sedimentation and exhibit significant anisotropy. To study the transverse isotropy characteristics of soil, the influence of intermediate principal stress and loading direction must be considered. Currently, research on transverse isotropy primarily focuses on the modified stress space, which is cumbersome to apply in multi-yield surface constitutive models. To describe the three-dimensional mechanical properties of geomaterials in real stress space, the α-Spatial Mobilized Plane strength criterion is introduced. Then, combined with the structure tensor, the transverse isotropic three-dimensional strength criterion can account for the effect of the loading angle. Finally, the three-dimensional strengths of Fukakusa clay, unsaturated SP-SC soils, uncemented Monterey sands, Yamaguchi marble, San Francisco Bay mud, Toyoura sand, and Santa Monica Beach sand are predicted on the π-plane. The results show that the αmn-SMP criterion, in the context of transverse isotropy, can describe the three-dimensional mechanical properties reasonably, and it can provide an accurate strength criterion for geotechnical engineering practice.

Optimization model for distributed energy trading based on a market value allocation mechanism in the electricity spot market

This study proposes a novel distributed energy trading market model with a value distribution mechanism to optimize the allocation and transactions of distributed energy resources (DERs). The framework incorporates a direct load management approach via an electricity aggregator agent, simplifying market processes and reducing transaction costs. A Nash bargaining model is employed to design a fair and efficient value distribution mechanism, promoting equitable benefit allocation among participants. The model integrates stochastic programming to account for uncertainties in real-time load and DER output, enhancing its robustness and applicability in real-world scenarios. The proposed mechanism quantifies each DER’s contribution using a market value contribution rate, serving as a foundation for the Nash bargaining model. This approach ensures individual rationality for both the aggregator and DERs while maximizing overall system benefits. Case studies validate the model’s effectiveness, demonstrating improvements in resource utilization and fair benefit allocation. This research contributes to the advancement of distributed energy markets, offering valuable insights for designing efficient and equitable market structures, ultimately promoting grid stability, renewable energy adoption, and the development of more sustainable and flexible energy systems.

Optimal Geometry for Focused Ion Beam-Milled Samples for Direct-Pull Micro-Tensile Testing Performed In Situ in a Scanning Electron Microscope

A thorough procedure was developed to efficiently manufacture dogbone samples using focused ion beam (FIB) milling for micro-tensile testing. A Bruker PI 89 PicoIndenter, Billerica, MA, USA, was used as a case study, although the analysis and results are applicable to other micro-mechanical testing systems capable of mounting a standard, Ø12.7 mm × Ø3.2 mm pin, scanning electron microscopy (SEM) pin stub (Ted Pella, Redding, CA, USA). Nine dogbones were made from an Fe-45Cu alloy additively manufactured using powder-fed laser-directed energy deposition (DED-LB). Testing showed that fracture was confined to the gauge section for all dogbones and that the fracture mode, ductile vs. brittle, was entirely dependent on the grain orientation relative to the loading direction. The analysis showed that the measured plastic strain to failure can vary from >11% (optimal geometry) to <1% (non-optimal geometry) in micro-tensile testing of high-tensile-strength (>1 GPa) metallic materials. Subsequently, a finite element analysis (FEA) was conducted to identify the improved dogbone geometries. A total of ten thousand dogbone geometries were tested, and their dimensions were defined by a set of four adjustable parameters (corner radius, load surface angle, load surface length, and dogbone head length). The gauge width and gauge length were fixed to 4 µm and 10 µm, respectively. Three-dimensional surface plots of the stress concentration as a function of two parameters were used to identify the optimal ranges of parameter values. The addition of maximum width and length constraints, measuring 25 µm and 30 µm, respectively, allowed us to identify an optimal geometry at load surface angles of 30° and 45°. Their respective dimensions (corner radius, load surface length, and dogbone head length) are, in µm, 12, 6, and 7 and 10, 7, and 7. Testing these two optimal geometries with a range of gauge lengths from 4 to 20 µm showed that smaller gauge lengths only slightly reduced the detrimental stress concentration outside the gauge section. However, smaller gauge lengths will notably improve the FIB surface polishing step as tapering is reduced with smaller dogbone lengths.

დატვირთული ბაგირის სტატიკური წონასწორული მდგომარეობის გაანგარიშება საწყის მონაცემთა მიმდევრობითი ვარიაციის გზით დრეკადი წაგრძელების გათვალისწინებით

The article discusses the task of implementing a discrete method for calculating the static equilibrium of suspended ropes in the modern programming language MS Visual Basic. A discrete general rope loading scheme for a rope suspended in a gravity field is proposed.Unlike analytical methods, it is possible to realize any number and direction load vector acting on the rope.The assignment and solution of the task can be given on the basis of the initial data given in the form of the length of the installation rope or the maximum tension of the rope.

Effect of Loading Direction on Tensile-Compressive Mechanical Behaviors of Mg-5Zn-2Gd-0.2Zr Alloy with Heterogeneous Grains

The tension-compression yield asymmetry caused by the strengthening of Mg-Zn-Gd-Zr alloy due to extrusion deformation is an important issue that must be addressed in its application. In this study, the effects of loading direction on the tensile and compressive mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy were systematically investigated. As the loading angle (the angle between the loading direction and the extrusion direction) increases from 0° to 30°, 45°, 60° and 90°, the tensile yield strength decreases more significantly than the compressive yield strength. Consequently, the tension-compression yield asymmetry is gradually improved. Additionally, the ultimate compressive strength decreases more markedly than the ultimate tensile strength with the increment of the loading angle. In tensile tests conducted at 0°, 30° and 45°, two distinct stages of decreasing strain hardening rates are typically observed. For the 60° and 90° tensile tests, one unusual ascending stage of strain hardening rate is observed. For all compressive tests, three stages of strain hardening are consistently noted; however, the increment in strain hardening rate caused by {10–12} extension twinning decreases with the increasing loading angle. A model combining loading angle and Schmid factor distribution was established. The calculated results indicate that the dominant deformation modes during the yielding process also vary significantly with the loading conditions. This clarification highlights the differences in yield strength variations between tension and compression. Finally, an analysis of the plane trace and crack propagation direction near the fracture surface reveals the fracture mechanisms associated with tensile and compressive tests at different loading directions. This study promotes understanding of the mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy under different loading directions, and helps to thoroughly elucidate the anisotropic effects of texture on the mechanical properties of magnesium alloys.

Modified Centroid of Root Projection Method for Determining the Center of Resistance of a Tooth

Abstract Center of resistance (CR) has been widely accepted in dentistry as a reference point for controlling tooth moment, which depends on the direction of loading and the morphology of the periodontal ligament (PDL). In clinical practice, dentists estimate the location of CR based on the morphology of the root of teeth, which may lead to a misestimation of orthodontic treatment. A quick method was proposed to efficiently determine the CR by identifying the centroid of the root projection (CRP), according to the orthodontic force. However, the original CRP method was limited to single-rooted teeth and it did not provide a strategy for handling the overlapping roots projection of multi-rooted teeth. To address this issue, we expanded the CRP method to accommodate multi-rooted teeth by applying the weighted average method. We further validated the modified CRP method using finite element simulation (FEA) for both single-rooted and multi-rooted teeth considering mesial-distal and buccal-lingual force directions. The evaluation of displacement distribution along the projection direction allowed us to assess translation and rotation movements, which confirmed that the centroid of root projection can accurately serve as the CR for the multi-rooted teeth. Additionally, we observed heterogeneous stress distributions in the multi-rooted teeth. Considering the well-acknowledged bone remodeling effect in response to local stress states, this indicated that the comprehensive indexes beyond the CR are desired for evaluating or controlling the tooth movement.

Evaluation on tension-compression anisotropic behavior of recycled asphalt mixture

The utilization of recycled asphalt pavement (RAP) is the effective way to improve resource conservation and reduce energy consumption. The asphalt mixture is a kind of typical anisotropic pavement materials due to its heterogeneity in composition and microstructure. This could lead to the differences of mechanical response between the tensile and compressive direction. However, there are limited researches to study the effect of RAP on the tension-compression anisotropic behavior of asphalt mixture. The strength, modulus and fatigue resistance tests are carried out and different loading modes are adopted. The results show that the tension-compression anisotropic behavior is more prominent with the increase of RAP content. The regenerant served as a kind of typical additive could alleviate this effect. In addition, the result of dynamic modulus test shows that the tension-compression anisotropic behavior has an increasing trend with the decrease of frequency and the increment of temperature. The ranking of fatigue life is opposite for the direct tensile and compressive loading mode, and the fatigue life ratio of compression to tension also show positive relation with the RAP content. Due to the difference in the stress mode, the fatigue life between the indirect tensile loading and four-point bending loading also show opposite trend, and the indirect tensile fatigue life has a larger discreteness.

Three-dimensional finite element analysis of stress distribution on different complex macro designs in commercially available implants: An in-vitro study

ObjectiveThis study aimed to investigate the effects of different commercially available complex implant macro designs on stress distributions using Finite element analysis. The experiment is done under varying simulated bone conditions to provide reference for clinical application. Materials and methodsThe study employed the Finite Element Analysis (FEA) method to compare four commercially available complex implant macro designs on a Computer-Aided Design (CAD) model of a maxillary bone segment. The three-dimensional geometrical model of the implants was reconstructed from computed tomography (CT)-slices in Digital Imaging and Communications in Medicine (DICOM) format and contact condition between the implant and the bone was considered as ‘Bonded’, implying perfect osseointegration. All materials used in the models were assumed to be isotropic, homogeneous, and linearly elastic. The Finite element simulations employed load of 400 N under both axial and non-axial conditions Stresses were analysed under different bone conditions. ResultsAverage values of von Mises stresses were used for comparing stress levels between implant designs. There was a definite increase in the equivalent stress values from higher density(D1)to lower density (D4) bone conditions for all implants. The percentage of increase ranged from 23.63 to 49.39 on axial loading and 20.39 to 57.19 when subjected to non-axial loading. The equivalent stress values resulted from non-axial loading were 1.78–2.94 times higher than that of axial loading for all implants under all bone densities. Among the complex designs Equinox Myriad Plus implant exhibited the least stress under axial loading (12.749–19.046 MPa) and (37.462–49.217 MPa) for non-axial loading. The stress on the crestal module was higher (1.49–2.99 times) than the overall stress on the implant regardless of the loading direction or bone conditions. ConclusionsData from the present study shows Equinox Myriad Plus implant generating the least equivalent stress and this can be taken as indicator in the biomechanical performance of the design.

Reliable comparison of multi-directional mechanical properties for biomimetic circle arc honeycombs

Abstract Compared to straight honeycombs, curved honeycombs derived from biomimetic strategies typically exhibit superior mechanical properties and a broader tunable range. Consequently, there has been a surge in research focusing on curved honeycombs. However, few studies have concurrently designed multiple honeycombs for reliable comparisons, and little attention has been given to isotropy. In this study, circle arc walls were introduced to replace the straight walls of five classical honeycombs, thereby creating representative curved honeycombs for analysis. The numerical modeling method in ANSYS software was validated by experimentally testing 3D printed specimens of circle arc honeycombs. At the same mass and under loading conditions in different directions, it was found that the Young's modulus, yield strength, Poisson's ratio, and energy absorption of circle arc hexagon (CAH), circle arc square (CAS), circle arc triangle (CAT), circle arc re-entrant (CAR), and circle arc double-V (CAD) were assessed. Both experimental and numerical results revealed that CAH demonstrates superior energy absorption while maintaining a high degree of isotropy, characterized by all isotropic factors below 0.1 in mechanical properties. Notably, CAD exhibits a Negative Poisson's ratio (NPR) effect across all loading directions. These results provide benchmarks for future studies on curved honeycombs and guide further research in this field.

High Mechanical Performance of Lattice Structures Fabricated by Additive Manufacturing

Lattice structures show advantages in mechanical properties and energy absorption efficiency owing to their lightweight, high strength and adjustable geometry. This article reviews lattice structure classification, design and applications, especially those based on additive manufacturing (AM) technology. This article first introduces the basic concepts and classification of lattice structures, including the classification based on topological shapes, such as strut, surface, shell, hollow-strut, and so on, and the classification based on the deformation mechanism. Then, the design methods of lattice structure are analyzed in detail, including the design based on basic unit, mathematical algorithm and gradient structure. Next, the effects of different lattice elements, relative density, material system, load direction and fabrication methods on the mechanical performance of AM-produced lattice structures are discussed. Finally, the advantages of lattice structures in energy absorption performance are summarized, aiming at providing theoretical guidance for further optimizing and expanding the engineering application potential of lattices.