Force-displacement Curves Research Articles

Analyses of the Suction Anchor–Sandy Soil Interactions under Slidable Pulling Action Using DEM-FEM Coupling Method: The Interface Friction Effect

The microscale mechanisms underlying the suction anchor–sandy soil interaction under slidable pulling actions of mooring lines remain poorly understood. This technical note addresses this knowledge gap by investigating the suction anchor–sandy soil interaction from micro to macro, with a particular emphasis on the effect of interface friction. The discrete element method (DEM) was utilized to simulate the sandy soil, while the finite element method (FEM) was employed to model the suction anchors. The peak pulling forces in numerical simulations were verified by centrifuge test results. The research findings highlight the significant influence of interface friction on the pulling force–displacement curves, as it affects the patterns of suction anchor–sandy soil interactions. Furthermore, clear relationships were established between the magnitude of interface friction, rotation angle, and pullout displacement of suction anchors. By examining the macro-to-micro behaviors of suction anchor–sandy soil interactions, this study concludes with a comprehensive understanding of failure patterns and their key characteristics under different interface friction conditions. The findings proved that the interface friction not only influences the anti-pullout capacity but also changes the failure patterns of suction anchor–soil interactions in marine engineering.

Identification of Individual Target Molecules Using Antibody-Decorated DeepTipTM Atomic-Force Microscopy Probes.

A versatile and robust procedure is developed that allows the identification of individual target molecules using antibodies bound to a DeepTipTM functionalized atomic-force microscopy probe. The model system used for the validation of this process consists of a biotinylated anti-lactate dehydrogenase antibody immobilized on a streptavidin-decorated AFM probe. Lactate dehydrogenase (LDH) is employed as target molecule and covalently immobilized on functionalized MicroDeckTM substrates. The interaction between sensor and target molecules is explored by recording force-displacement (F-z) curves with an atomic-force microscope. F-z curves that correspond to the genuine sensor-target molecule interaction are identified based on the following three criteria: (i) number of peaks, (ii) value of the adhesion force, and (iii) presence or absence of the elastomeric trait. The application of these criteria leads to establishing seven groups, ranging from no interaction to multiple sensor-target molecule interactions, for which force-displacement curves are classified. The possibility of recording consistently single-molecule interaction events between an antibody and its specific antigen, in combination with the high proportion of successful interaction events obtained, increases remarkably the possibilities offered by affinity atomic-force microscopy for the characterization of biological and biomimetic systems from the molecular to the tissue scales.

A wear testing method of straight blade tools for Nomex honeycomb composites machining

Ultrasonic vibration machining (UVM) with a straight blade tool (SBT) is currently an efficient process for part manufacturing of Nomex honeycomb composites (NHCs) in the aerospace industry. To solve the wear evaluation problem of SBT, this study focused on the failure characteristics of tool edge blunting, which was different from that of traditional metal-cutting tools. The edge radius measured by ultra-depth microscope and a dimensionless parameter Bluntness Coefficient (CB) obtained from fiber-cut sharpness test were applied to evaluate SBT wear. The fiber-cut sharpness test was realized by a two-stage model proposed based on fiber failure analysis and force-displacement curve, which were validated by experiments. A standardized testing device was established based on the model, and a relationship between edge radius and CB was obtained by testing quantitatively blunted SBTs. Machining experiments were carried out to obtain a correlation between tool performance and CB, and a failure standard of CB value for SBT was proposed. It was demonstrated that CB was an efficient indicator for SBT wear evaluation, and the sharpness testing by cutting fibers could characterize SBT wear with favorable accuracy and repeatability.

Modelling and characterization of novel honeycomb structures with mass gradient produced by additive manufacturing

The dissemination of additive manufacturing methods has facilitated the design and production of complex structures which have a high strength-to-weight ratio. Cellular materials such as honeycombs have low-weight and high capacity to absorb energy which makes them desirable for the aerospace and automotive industries. The present work covers the study and comparison of metal-based regular honeycombs and functionally graded honeycombs. The latter encompass radial and linear/longitudinal gradients. Three repeating unit cells were studied: regular hexagons, Plateau and lotus. The structures were produced in aluminium using the laser powder bed fusion technique. Selected samples were submitted to a stress-relieving heat treatment. Numerical and experimental methods were used to assess the in-plane compressive properties. Finite element analysis was used to obtain the simulated force–displacement curves of each structure, allowing for the calculation of specific stiffness, absorbed energy and yield strength. The experimental method consisted of the compression of three specimens of three types of regular structures with and without stress-relieving heat treatment. The heat treatment reduced the yield strength and stiffness whilst increasing the ductility of the samples. The mechanical behaviour of the structures was found to depend upon a combined effect of the type of gradient, relative density, and unit cell structure. The results showed that an increase in the relative density would enhance the specific mechanical properties. The lotus configuration displayed the highest specific mechanical properties, as its geometry reduces the stress concentrations. The numerical results showed a reasonable match with the experimental results.

Design and analysis of a tunable multistable mechanical metamaterial

Multistable mechanical metamaterials can have unusual properties that facilitate promising applications, including reusable vibration isolation and efficient energy absorption. In this paper, we propose a tunable multistable mechanical metamaterial (TMMM) that is capable of independent and continuous adjustment of its post-fabrication mechanical properties. The unit cell of the TMMM consists of a sinusoidal beam and several supporting beams, with its mechanical behavior finely tuned by inserting specially designed connecting beams into the gaps of the supporting beams. We adopt a combined theoretical and numerical approach to explore the effect of geometric parameters and identify the design space of monostability and bistability. Based on the unit cell, a multilayer TMMM is designed and fabricated and its tunable mechanical response is investigated. The results show that not only the force-displacement curves but also the snap-through behavior and deformation order can be tuned in a straightforward manner. The proposed design has the potential to enhance the development of multistable mechanical metamaterials and broaden their applications in engineering scenarios with varying demands.

Promoting bridging in adhesively bonded composites with polymer inserts: A computational perspective

Preventing catastrophic failure due to delamination in adhesively bonded carbon fiber reinforced polymer (CFRP) is crucial to enhancing the reliability of structures. Experimental evidence from another study demonstrated that introducing inserts into the adhesive bond line creates bridging, effectively arresting the delamination process. In this paper, a numerical model was proposed to mimic the experiment and then utilized for conducting parametric studies. An embedded cell approach was adopted, representing a double cantilever beam (DCB) with linear-elastic continuum shell elements, beam elements for the bridging bundles, and connector elements for the adhesive. The crack propagation was initiated with adhesive failure and subsequently followed by bridging bundle failure. The numerical simulation results closely replicated the experiment’s global response in the force–displacement curve, thereby effectively validating the existence of the bridging effect. Furthermore, our study revealed that enhancing the adhesive strength and insert ductility can further improve crack resistance.

Multiscale modeling of unfolding and bond dissociation of rubredoxin metalloprotein

Mechanical properties of proteins that have a crucial effect on their operation. This study used a molecular dynamics simulation package to investigate rubredoxin unfolding on the atomic scale. Different simulation techniques were applied, and due to the dissociation of covalent/hydrogen bonds, this protein demonstrates several intermediate states in force-extension behavior. A conceptual model based on the cohesive finite element method was developed to consider the intermediate damages that occur during unfolding. This model is based on force-displacement curves derived from molecular dynamics results. The proposed conceptual model is designed to accurately identify bond rupture points and determine the associated forces. This is achieved by conducting a thorough comparison between molecular dynamics and cohesive finite element results. The utilization of a viscoelastic cohesive zone model allows for the consideration of loading rate effects. This rate-dependent model can be further developed and integrated into the multiscale modeling of large assemblies of metalloproteins, providing a comprehensive understanding of mechanical behavior while maintaining a reduced computational cost.

Model-experiment comparison of quasi static loading on a composite overwrap pressure vessel (Part 2)

A methodology to develop a 3D Finite Element (FE) model of a full metal-lined Composite Overwrapped Pressure Vessel (COPV) was developed and is presented in this paper. The model is intended for prediction of the metal-composite delamination and residual dent depth developed in the metal liner as a result of quasi-static indentation loading. Cohesive elements are used to model the composite and the metal-composite interfaces. Experimental and numerical comparisons of force–displacement curves, delamination area and residual dent depth are presented. Numerical results are in good agreement to the experimental data.

Effect of curing stress on the interface property of cement-treated dredged mud and geogrid

The cement-treated dredged mud mixture is suitable for backfill in earthwork projects because of its high water content and flowability. Incorporating geogrid can enhance the mixture’s tensile strength. Constructing with cement-treated mud at greater heights generates curing stress, affecting the interface with geogrid. Pullout tests were performed to analyze the impact of curing stress, water content, and cement content on the interface performance. Results showed similar pullout force-displacement curves regardless of curing stress, indicating strain-softening behavior. Higher water content resulted in decreased pullout forces, while higher cement content led to increased pullout forces. Samples under curing stress exhibited increased peak pullout forces ranging from 2% to 70% compared to samples without curing stress. The rate of increase in pullout force because of curing stress decreased with higher water or cement contents. Curing stress influenced the interface friction angle in specimens with water contents 1.5 and 2 times the liquid limit. It significantly affected the interface cohesion in samples with water contents 2.5 times the liquid limit. Samples subjected to curing stress demonstrated a higher apparent friction coefficient, with an average increase ranging from 4% to 43%, which decreased with higher water content and lower cement content, regardless of curing stress.

Buckling behavior of soft spherical shells with patterned surface under indentation

A well understanding of instability mechanics of soft shell structures is key issue due to its important implications in functional shape morphing, flexible electronics, soft robotics, nanotechnology, biological engineering, etc. Despite abundant studies, buckling analysis of flexible shells with patterned surface under indentation is rare, primarily because of the complexities of high nonlinearities in geometry, material, and surface contact. In this paper, buckling behavior of spherical shells with patterned surface under indentation is comprehensively investigated by using experimental, numerical and theoretical analyses. It is found shells with stripes show similar variation in the force-displacement curves and post-buckling morphologies like perfect shells. Unlike perfect ones, shells with discontinuous protrusions exhibit multiple snap-through due to local buckling under indentation. What is more, mechanical response and buckling morphology can be well controlled by tuning shell thickness as well as positions and sizes of protrusions. These results can not only deepen understanding of mechanism of spherical shell buckling under local loads, but also provide a designing guidance for flexible electronics, soft robotics, and other future devices.

Experimental evaluation on the mitigation performance of double-layered Kirigami corrugated cladding against impact load

The impact mitigation performance of novel single and double-layered kirigami corrugated (KC) claddings is investigated in this study via drop weight impact tests, as their significant improvements in energy absorption and crushing resistance were previously demonstrated over conventional corrugated structures. The feasibility of mass production on the proposed large-size KC core is also verified by applying conventional multi-stage mould pressing. A total of 15 different configurated single and double-layered KC cladding specimens are prepared and tested, where the effects of impacting speed, impacting mass, layer number, stacking configurations as well as graded design on the impact mitigation performance are considered. Impact force time histories, impact force-displacement curves, and transmitted force time histories at five different locations recorded using a custom-made measuring system are compared to evaluate the impact mitigating performance for the structure placed behind the proposed protective KC claddings. Transmitted force at centre is reduced by more than half as compared with the applied impact force for all double-layered KC claddings. Among the double-layered KC claddings, inverse symmetrically stacked KC cladding with no offset in the bottom layer, as well as the negatively graded KC claddings demonstrate a superior performance with a lower transmitted peak force at the centre and a more uniform force distribution transmitted to the support behind the claddings.

Assessing critical fracture energy in mode I for bonded composite joints: A numerical–experimental approach with uncertainty analysis

The manufacturing process of composite structural components involves the assembly of composite parts using adhesives, which introduces variations in the geometrical and mechanical properties of bonded joints. The fracture energy under mode-I loading ( G I c) is a parameter used to predict crack propagation and evaluate the residual strength of the joint. This work proposes a numerical-experimental procedure to determine G I c in mode I, while considering the uncertainties inherent in the manufacturing process of bonded joints. The proposed procedure employs a three-dimensional finite element model to simulate a double cantilever beam test, using finite element commercial software. The cohesive zone model is applied to simulate the mechanical behavior of the adhesive, and experimental data are used to feed the computational model. A Plackett-Burman design is performed to reduce the number of experiments and evaluate the effect of the main influence parameters. Force-displacement curves are obtained, the compliance-based beam method is applied to determine G I c in mode I, employing both trapezoidal and triangular traction-separation laws. The results are thoroughly examined, taking into account the potential strengths and limitations of the proposed procedure, particularly in its application to predicting the behavior of bonded composite joints under mode I loading conditions. The proposed approach can help to understand the uncertainties effect related to the manufacturing process of bonded joints on G I c values, and improve the reliability of predicting crack propagation and residual strength assessment in bonded joints.

Research on low‐velocity impact resistance of carbon fiber composite laminates

AbstractThis research conducts a comprehensive experimental and numerical analysis of carbon fiber composite laminates under low‐velocity impact conditions. Split Hopkinson Pressure Bar (SHPB) was employed to conduct impact testing on laminates with two layup sequences ( and ) under impacts ranging from 2 to 6 J. For assessing damage in laminates, a comprehensive progressive damage model and a simplified model were developed. The primary distinction between these models lies in the fact that the former incorporates the strengthening effect of compression on the delamination behavior, while the latter does not. Both models produce a good agreement with experimental results in terms of force–time, force–displacement curves, and absorbed energies. However, notable differences were noted in the predicted internal damage; the simplified model was underpredicted in terms of damage size and distribution compared to the comprehensive progressive damage model.Highlights Impact tests were conducted on and composites. In order to simulate damage caused by impacts in laminates, an energy‐based damage model was created, and cohesive elements were utilized to model interlaminar delamination. The strengthening effect of compression was explored. Distinct damage criteria were established for two cases. Damage detection of composites by x‐rays.

Bending performance and failure modes of sinusoidal corrugated sandwich panels fabricated using stereolithography technology: Effects of geometric parameters

The sinusoidal wave corrugated sandwich panel is an exceptional component with outstanding performance, making it highly suitable for both military and civilian applications. Its strength, rigidity, lightweight nature, low density, simple structure, cost-effectiveness, high load-carrying efficiency, remarkable load-bearing capacity, as well as excellent sound insulation and thermal insulation properties, have positioned the sinusoidal wave corrugated sandwich panel as an ideal choice for energy absorption devices. To evaluate the bending performance of the sinusoidal wave corrugated sandwich panel, this study fabricated single-layer and double-layer sinusoidal wave core sandwich panels using the light-curing molding process described in this research. The research analyzed the impact of various geometric parameters, including skin thickness, core layer thickness, core height, and corrugation wavelength, on the bending performance and failure modes of the single-layer sinusoidal wave core sandwich panels through three-point bending loading tests. The failure modes of the sinusoidal wave corrugated sandwich panel were validated using finite element simulation. Additionally, the study examined the bending performance of the sandwich panels with double-layer sinusoidal wave cores and investigated the influence of wavelength distribution in the upper and lower core layers on the force–displacement curve and energy absorption capacity of the double-layer sinusoidal wave core sandwich panel. These findings provide valuable theoretical support for the design of lightweight and high-strength sandwich panels.

Load Deflection Characteristics of Orthodontic Gummetal® Wires in Comparison with Nickel-Titanium Wires: An In Vitro Study.

The aim of this study was to investigate the load deflection characteristics of Gummetal® wires in comparison to nickel-titanium (NiTi) wires. Four different NiTi wires and one Gummetal® archwire were analyzed in two dimensions (0.014″ (0.36 mm) and 0.016″ × 0.022″ (0.41 mm × 0.56 mm)) and in two different orientations (edgewise and ribbonwise) using three-point bending tests at T = 37 °C. Force-displacement curves were recorded and analyzed. The Gummetal® 0.014″ wires exhibited higher forces compared to the NiTi wires at 2.0 mm deflection. At 1.0 mm deflection, the opposite pattern was observed. For the 0.016″ × 0.022″ Gummetal® wires, the forces were within the force interval of the NiTi wires at 2.0 mm deflection. At a deflection of 1.0 mm, no residual force was measurable for the Gummetal® wires. All the NiTi wires investigated showed hysteresis and a superelastic plateau. However, the Gummetal® did not form a plateau, but hysteresis was present. An easier plastic deformability compared to the NiTi wires was observed for all the tested geometries.

Tel Eritmeli İlkörnekleme (FDM) ile Üretilen Sandviç Yapıların Mekanik Davranışı Üzerinde Dolgu Parametrelerinin Etkisinin İncelenmesi

This study focuses on the investigation of infill patterns and their influence on the mechanical behavior of sandwich structures fabricated using the Fused Deposition Modeling (FDM) technique. Polylactic Acid (PLA) was chosen as the primary material, known for its favorable mechanical properties and biodegradability. Six different infill patterns, including Cubic, Line, Triangular, Trihexagonal, Octet, and Gyroid, were employed to fabricate sandwich structures with varying infill densities (20%, 30%, and 40%). The samples were subjected to edgewise compressive strength tests, and the force-displacement curves were analyzed to evaluate the performance of the structures. The results revealed that the Cubic infill pattern exhibited superior strength in all infill densities, while other patterns showed variations in performance. Moreover, the analysis of damage types indicated different failure modes, such as core shear and facesheet buckling, depending on the infill pattern and density. These findings contribute to understanding the role of infill patterns in enhancing the mechanical properties of sandwich structures fabricated via FDM.

Energy dissipation evaluation of butterfly-shaped steel plate shear keys under different loading protocols

This paper proposes a novel energy dissipation shear key (ED shear key) for small-to-medium-span highway bridges using butterfly-shaped steel plates for enhanced energy dissipation capacity. Reversed cyclic loading tests were conducted on two series of specimens which had different designs of structural dimensions. Four distinctive loading protocols were adopted to allow an in-depth examination of the seismic hysteretic behavior and energy dissipation capacity of the ED shear keys. The test results reveal that the ED shear keys exhibited distinctive characteristics before and after buckling of steel plates. The recorded force-displacement curves of the ED shear keys were plump before buckling and typically became pinched after buckling. The loading protocol had a significant effect on the energy dissipation of the ED shear key specimens, with an over 90% increase in energy dissipation observed under the constant-amplitude loading protocol compared to the incremental-amplitude ones. It was found from the test results that the profile of the force-displacement skeleton curves was hardly affected by the loading protocols, as a result a trilinear skeleton model is developed to characterize the force-displacement relationship of the ED shear keys. Furthermore, by decomposing the force-displacement hysteresis curve into a skeleton part and a Bauschinger part, an evaluation model is established for predicting the energy dissipation capacity of the ED shear keys. Validation against the test results indicates that the evaluation model can provide a satisfactory accuracy for predicting the energy dissipation of the ED shear keys subjected to various loading protocols.

Modified post-installed adhesive anchorage test: Investigation of in-place compressive strength of concrete and influential factors

This paper presents the Modified Post-installed Adhesive Anchorage test (MPAA) as a method for evaluating the in-place compressive strength of concrete. It considers various influential factors, including test surface characteristics, concrete strength, anchorage depth, bolt diameter, and rebar location. Additionally, a formula for calculating concrete compressive strength, applicable to various influencing factors, was suggested. The findings demonstrate the effectiveness of MPAA in assessing in-place compressive strength of concrete with a high degree of precision. Following pull-out test, the prevalent failure modes observed were vertebral failure and vertebral-bond composite failure. Moreover, diverse concrete strengths, anchorage depths, and rebar locations demonstrated differing impacts on failure modes, while test surface characteristics and bolt diameter exerted less noticeable effects. The pull-out force-displacement curve during pull-out displayed three discernible phases: the elastic phase, crack propagation phase, and descent phase. When conducting on-site assessments, it is advisable to situate test points on the side surfaces of the members. Furthermore, factors like cover thickness and rebar location should be thoroughly evaluated when positioning test points. This encompasses the prudent choice of anchorage depth and bolt diameter to improve test precision. The suggested formula for calculating compressive strength exhibited minimal error and is applicable in determining concrete compressive strength for a wide range of practical engineering contexts. This study not only establishes a theoretical underpinning and offers support for standard revisions but also furnishes valuable guidance for conducting on-site testing procedures.

4D printed zero Poisson’s ratio metamaterials with vibration isolation properties for magnetic response

Although mechanical metamaterials possess high specific energy absorption, they suffer from drawbacks such as irreversible deformations and non-adjustable mechanical properties. Magnetic excitation is considered to be one of the most promising methods for special working environments; for which uniform incorporation of UV-cured four-dimensional (4D) printed resin is considered to be an effective approach to achieving fine structural features. Our study investigated the impact of soft magnetic particle content on the mechanical and dynamic mechanical properties of a shape memory polymer matrix material. This paper presents a 4D printed metamaterial with a zero Poisson’s ratio that can sense magnetic field intensity and alter its mechanical properties. Its rapid shape recovery, achieved through magnetic excitation, enables multiple energy absorption within a short timeframe. By increasing the curvature radius, the stress concentration in the hexagonal honeycomb structure is reduced, ensuring the metamaterial maintains its zero Poisson’s ratio even under in-plane loading. The study investigates the energy absorption performance and force–displacement curve of metamaterials with different layers and cell sizes, focusing on a four-layer metamaterial for the analysis. Furthermore, the paper explores the tunable energy absorption characteristics of the four-layer metamaterial under time-varying electromagnetic fields, aiming to enhance the stability of a lander’s center of gravity while landing on uneven terrain.

Texture Analysis of Chinese Dried Noodles during Drying Based on Acoustic-Mechanical Detection Methods.

To better understand the textural transformation of Chinese dried noodles during the drying process, a convenient acoustic-force detection method was established. By comparing the breaking point, it was possible to determine the time-scale correlation between the force-displacement curves and acoustic spectrograms. The acoustic eigenvalues showed a consistent upward trend with the mechanical parameters during the drying process. With a wave crest reaching 152.8 dB and a signal maximum reaching 0.072, the structural stability of the dried noodles hardly induces a higher acoustic response. This suggests that the mechanical strength and rigidity of the dried noodles undergo minimal changes during this period. In comparison to the mechanical parameters, the acoustic eigenvalues accurately describe the changes in texture of dried noodles under various drying conditions, moreover, the sound threshold also provides a more effective response to the dried noodles' structural strength threshold. Therefore, the acoustic detection method can be applied to assist the conventional mechanical measurement in the field of the texture evaluation of dried food.