Global Mechanical Behavior Research Articles

Methods for characterization and continuum modeling of inhomogeneous properties of paper and paperboard materials: A review

The potential of paper and paperboard as fiber-based materials capable of replacing conventional polymer-based materials has been widely investigated and evaluated. Due to paper’s limited extensibility and inherent heterogeneity, local structural variations lead to unpredictable local mechanical behavior and instability during processing, such as mechanical forming. To gain a deeper understanding of the impact of mechanical behavior and heterogeneity on the paper forming process, the Finite Element Method (FEM) coupled with continuum modeling is being explored as a potential approach to enhance comprehension. To achieve this goal, utilizing experimentally derived material parameters alongside stochastic finite element methods allows for more precise modeling of material behavior, considering the local material properties. This work first introduces the approach of modeling heterogeneity or local material structure within continuum models, such as the Stochastic Finite Element Method (SFEM). A fundamental challenge lies in accurately measuring these local material properties. Experimental investigations are being conducted to numerically simulate mechanical behavior. An overview is provided of experimental methods for material characterization, as found in literature, with a specific focus on measuring local mechanical material structure. By doing so, it enables the characterization of the global material structure and mechanical behavior of paper and paperboard.

Abstract 1007: A Novel Heterogeneous Murine Aortic Model Derived From Micro-computed Tomography

Introduction: Strength and structural stability of the aorta primarily comes from collagen that is mostly found in the media layer of the aorta along with elastin. The risk of life-threatening aortic rupture increases in cases of aortic aneurysm diseases due to local deformation and weakening of the aortic wall. How does local structure affect how the aorta responds to stress? We hypothesize that material and geometric heterogeneity affect the local biomechanics of the aortic wall and that the local responses to stress are not necessarily the same as the global response. Our goal is to develop a novel finite element model (FEM) of collagen and elastin behavior in murine aorta derived from high-resolution micro-computed tomography (microCT). This model will allow us to study how the aorta deforms to blood pressure at the local level. Approach: The collagen and elastin from 100 vertical slices of microCT scans of a murine aorta were segmented, smoothed and meshed to create 3D models for FEM and the aortic ring was divided into 8 sections of varying geometry and composition. Local stress-strain relationships were extracted from uniaxial loading conditions. Simulations were conducted where the stiffness of collagen was set equal to (1X) or made stiffer than elastin by a factor of 10 (10X) or 100 (100X). The average Young’s modulus, E, for each section was calculated and used as parameters for FEM of the aortic ring to investigate the global mechanical behavior of the aortic wall. Results/Conclusions: The strains generated in the radial direction are greater than the strains in the hoop direction in each of the 8 heterogeneous sections of the aortic ring. There was significant variability in the E values in the 10X and 100X systems. FEM of a materially uniform aortic ring yielded smaller maximum principal logarithmic strains compared to a ring that was materially heterogeneous. This study provides evidence that local structure and material distribution are important in aortic biomechanics. Pathogenesis of aneurysmal disease is dependent on collagen and elastin turnover. Aneurysm rupture results from mechanical failure: peak wall stress exceeds local tissue strength. This novel method will allow for development of a complex aortic fracture model to study aortic pathologies.

Finite Element Modeling of Cells Adhering to a Substrate: An Overview

In tissue formation and regeneration processes, cells often move collectively, maintaining connections through intercellular adhesions. However, the specific roles of cell–substrate and cell-to-cell mechanical interactions in the regulation of collective cell migration are not yet fully understood. Finite element modeling (FEM) may be a way to assess more deeply the biological, mechanical, and chemical phenomena behind cell adhesion. FEM is a powerful tool widely used to simulate phenomena described by systems of partial differential equations. For example, FEM provides information on the stress/strain state of a cell adhering to a substrate, as well as on its mechanobiological behavior. This review paper, after briefly describing basic principles of cell adhesion, surveys the most important studies that have utilized FEM to investigate the structural response of a cell adhering to a substrate and how the forces acting on the cell–substrate adhesive structures affect the global cell mechanical behavior.

Aeroelasticity analysis of anisogrid lattice sandwich cylindrical shells: Extended potential and piston theories

Based on the extended potential and piston aerodynamics theories, buckling and vibration analysis of sandwich cylindrical shells subjected to external airflow in both subsonic and supersonic regimes is presented. Sandwich cylindrical shells are considered to be made of same homogenous face sheets and an anisogrid composite lattice core with hexagonal cells. An equivalent single layer (ESL) theory in the framework of classical Love’s shell theory is used to formulate the global mechanical behavior of such shells. According to the extended potential and piston aerodynamic theories, aerodynamic pressure distributions are determined for steady, inviscid, irrotational compressible, and external airflow. The closed–form solutions of critical upstream pressure and natural frequency are developed for different boundary conditions using the Galerkin method. Finally, case studies are presented to compare between results of extended potential and piston theories and investigate the effects of upstream speed, geometric ratios, boundary conditions, and lattice specifications on various response quantities. Findings indicate that the differences in results of extended potential and piston theories are less than 3% in the supersonic regime with 2.3 ≤ M ∞ ≤ 2.7 for intermediate-length shells with a wide range of R . The piston theory is inadequate for analyzing aeroelasticity behavior of very long thin sandwich cylindrical shells.

Study of Mechanical Properties, Microstructure, and Residual Stresses of AISI 304/304L Stainless Steel Submerged Arc Weld for Spent Fuel Dry Storage Systems

The confinement boundaries of spent nuclear fuel (SNF) canisters are typically fusion welded. Welded microstructures, strain hardening, and residual stresses combined with a chemically aggressive, chloride-rich environment led to concerns that the welded canister may be susceptible to chloride-induced stress corrosion cracking (CISCC). A comprehensive understanding of the modification of stainless steel (SS) metallurgical and mechanical properties by fusion welding could accelerate the predictive analysis of CISCC susceptibility. This paper describes a submerged arc welding (SAW) procedure that was developed and qualified on 12.7 mm (0.5 in.) thick AISI 304/304L SS to produce joints in a way similar to actual SNF canister manufacturing. This procedure has the potential to reduce the production cost and weld CISCC susceptibility by using fewer welding passes and lower heat input than current industrial applications. Global and local mechanical behaviors and properties, as well as residual stress distributions on the welded joint, were studied. The results indicate that hardness values in the fusion zone (FZ) and heat-affected zone (HAZ) are slightly higher than that of the base metal. Strain localization was presented in the HAZ before the tensile stress reached its maximum value, and then it shifted to the FZ. The specimen finally broke in the FZ. High tensile residual stresses exhibited in the FZ and the nearby HAZ suggest the highest CISCC-susceptible spots. The maximum tensile residual stresses were along the welding direction, indicating that if cracks occur, they would be perpendicular to the welding direction. This study involved developing and qualifying a SAW procedure for SNF canister production. The new procedure yielded cost savings (SAW working efficiency increased by about 80%), improved mechanical properties, and presented moderate residual stresses. Analysis revealed that the welded joint’s low-stress and high-stress damage assessments may be affected by shifts in the strain localization spot under loading.

Study of self-heating and local strain rate in polyamide-6 and short fibre glass/polyamide-6 under tension through synchronised full-field strain and temperature measurements

This paper studies thermomechanical coupling during room-temperature tensile testing of polyamide-6 (PA6) and 50 wt% short glass fibre/PA6. The tests were performed for different fibre angles (0°, 45°, 90°), moisture contents (dry, 50%RH), and strain rates (10−4, 10−2, 10−1s−1). Digital image correlation (DIC) was coupled with infrared thermography. The contribution of the local strains, strain rates and temperatures to the global mechanical behaviour was investigated throughout deformation. The initial thermoelastic response was used to estimate the coefficient of thermal expansion. In PA6, neck development caused significant self-heating at high strain rates, differently between dry and 50%RH. In glass/PA6, however, temperature rises were always small (<+3 °C) despite local strain rate peaks in the fracture zone. This was ascribed to limited plastic deformation, as confirmed by post-mortem microscopy. The full-field data can be highly valuable for the development of advanced constitutive models for both pure polymer and short fibre composite.

Bio‐based laminated truss structures with bolted steel connections: Experiment, modeling, and model‐updating

AbstractBio‐based laminated structures offer a timely solution to meet the pressing demand for resource‐efficient and environmentally responsible construction practices in civil engineering. Bolted connections are commonly used in truss joints and significantly impact their global mechanical behaviors. However, existing studies on the complex behavior of joints for integrated bio‐based structures are lacking. Based on previous work by the authors about joint behavior, this study seeks to experimentally investigate the axial behavior of bolted steel to laminated timber and bamboo (glubam) connections with slotted‐in steel plates in planar truss structures. First, cyclic tests were conducted on Bio‐based laminated planar truss structures to evaluate their global and local hysteretic behavior. The test matrix encompasses eight distinct connection configurations, carefully selected to assess the connection behavior of Laminated Veneer Lumber (LVL) and Glued Laminated Bamboo (glubam). Subsequently, through the incorporation of the hysteretic model for truss joints, an advanced hybrid truss model was developed within the OpenSees framework and successfully validated using experimental data. Finally, this study proposes and demonstrates the effectiveness of an efficient model‐updating framework, which combines the power of the genetic algorithm (GA) and neural network, resulting in a significantly enhanced accuracy of the model.

Identification of the effective interface between the homogenized phases of a dual-weave 3D composite

Hybridization enhances composite properties by assembling several reinforcement materials. In woven composites, the distribution of different yarns can induce a macroscopic heterogeneity in the thermomechanical properties, which can be considered in the modeling through the introduction of homogenized phases regionally. Identifying the interfaces between those effective phases based on the geometry is difficult due to the yarn entanglement at the interfaces. This work proposes to identify the optimal positions of interfaces by observing the global mechanical behavior of the composite. An asymmetric glass/carbon-hybrid 3D-interlock fabric is studied. It results in a dual-weave composite modeled as macroscopically bi-phased material. It is shown that the effective interface position can be determined from a heating-cooling experiment tomographied in-situ, and processed by Integrated Digital Volume Correlation (IDVC), together with some of the thermomechanical properties of each phase. To enhance IDVC sensitivity, a specific procedure is designed to include the specimen boundary in the analysis.

The effect of contaminating media on the static and dynamic mechanical resilience of dental implant abutments' screws: In vitro study.

This in vitro study aims to biomechanically evaluate the influence of medium contamination for example, saliva, blood, chlorhexidine (liquid and gel), and fluoride mouthwash on the biomechanical behavior of implant abutments' screws under static and dynamic loading. Forty five Ti6Al4V commercial dental implants and abutments were tested in this study. Two main mechanical tests were carried out in the selected media. The first, static, aimed to evaluate the torque loss after the first tightening. The second, dynamic, involved a random cyclic load range between 0 and 200 N to evaluate torque loss due to mastication. In addition, metallographic longitudinal and cross-sections of the abutment-implant apparatus were examined to evaluate the abutment screw-abutment-implant interface. The static torque test showed that irrespective of the media, no statistical difference in static torque loss was found prior to dynamic loading. For the dynamic tests, torque-angle evolution analysis during tightening to 30 Ncm and after the spectrum loading, showed the same global mechanical behavior for all media, but the statistical analysis indicated a difference between the groups in reverse torque values (RTV) and in the torque loss due to dynamic loading. The medium groups CHX, CHX-gel, and Fluoride mouthwash, showed a meaningful torque loss due to loading, but the medium groups, control (no medium), blood and saliva showed an opposite trend and required a higher torque to open the abutment screws. The microstructural analysis revealed clear signs of cold-welding/galling, post-dynamic loading in these latter groups. The presence of lubrication/contamination media (CHX mouthwash/CHX-gel/Fluoride mouthwash) reduces the preload generated due to tightening but prevents damage due to galling. The observed reduction of RTV clearly emphasizes the need for frequent abutment screw retightening for implant-supported prosthetic long-term stability.

Multi-fidelity machine learning based uncertainty quantification of progressive damage in composite laminates through optimal data fusion

Recently machine learning (ML) based approaches have gained significant attention in dealing with computationally intensive analyses such as uncertainty quantification of composite laminates. However, high-fidelity ML model construction is computationally demanding for such high-dimensional problems due to the required large amount of high-fidelity training data. We propose to address this issue effectively through multi-fidelity ML based surrogates which can use a training dataset consisting of optimally distributed high- and low-fidelity simulations. For forming multi-fidelity surrogates of progressive damage in composite laminates, we combine low-fidelity finite element analysis data obtained using Matzenmiller damage model with Hasin failure criteria and high-fidelity finite element analysis data obtained using three-dimensional continuum damage mechanics based model with P Linde’s failure criteria. It is shown that there is a significant computational advantage to using the multi-fidelity surrogate approach as compared to conventional single-fidelity surrogates. Such computational advantage through optimal data fusion without compromising accuracy becomes crucial for the subsequent data-driven uncertainty quantification and sensitivity analysis of composites involving thousands of realizations. Ply orientations come out to be the most sensitive parameters to matrix damage, fibre damage and reaction force in composite laminates. The degree of uncertainty in the output quantities depend on the input-level stochastic variations. For example, a combined stochastic variation of ±10% in material properties and ±10° in ply orientations lead to 1.85%, 16.98% and 11.24% coefficient of variation in the matrix damage, fibre damage and reaction force respectively. In general, the numerical results obtained based on the efficient data-driven approach strongly suggest that source-uncertainty of composites significantly influences the progressive damage evolution and global mechanical behaviour, leading to the realization of the importance of adopting an inclusive analysis framework considering such inevitable random variabilities.

Effective elastic moduli of space-filled multi-material composite lattices

Traditionally lattice materials are made of a network of beams in two and three dimensions with majority of the lattice volume being void space. Recently researchers have started exploring ways to exploit this void space for multi-physical property modulation of lattices such as global mechanical behaviour including different elastic moduli, wave propagation, vibration, impact and acoustic features. The elastic moduli are of crucial importance to ensure the structural viability of various multi-functional devices and systems where a space-filled lattice material could potentially be used. Here we develop closed-form analytical expressions for the effective elastic moduli of space-filled lattices based on an exact stiffness matrix approach coupled with the unit cell method, wherein transcendental shape functions are used to obtain exact solutions of the underlying differential equation. This can be viewed as an accurate multi-material based generalisation of the classical formulae for elastic moduli of honeycombs. Numerical results show that the effective in-plane elastic moduli can increase by orders of magnitude with a relatively lower infill stiffness (∼10%). This gives an exceptional opportunity to engineer multi-material lattices with optimal specific stiffness along with characterising the mechanical properties of a multitude of lattice-like artificial and naturally occurring structural forms with space filling.

A computationally efficient finite element model for the analysis of the non-linear bending behaviour of a dynamic submarine power cable

This paper proposes a numerical approach based on a detailed 3D FE model to calculate the global mechanical behaviour and local stress state of dynamic submarine power cables. The method is applied to a three-core dynamic submarine power cable under a cyclic bending load. The numerical approach is based on the homogenization theory of periodic structures. The 3D computational domain is thus reduced to the helical period of the internal cable components, which allows the geometrical complexity and contact interactions between the components to be fully considered. In addition, the mesh size is reduced by using beam element modelling of the armour components. The study investigates the sensitivity of the cable bending behaviour to frictional interactions and manufacturing residual stresses. To validate the numerical model, the results are compared with experimental data and analytical results. The first comparison focuses on the overall behaviour of the cable under a cyclic bending load, while a local analysis compares quantities such as displacement and stresses with the results of analytical models available in the literature. The close agreement between the numerical, experimental and analytical results demonstrates the accuracy of the model in predicting the non-linear bending behaviour and local stresses that are essential for the cable design process.

Small-depth nanoindentation studies of an additively manufactured titanium alloy: Anisotropic nanomechanical properties and correlation with microscopic mechanical behaviour

Nanoindentation has been widely used to measure local mechanical properties of heterogeneous materials. The nanohardness (H), typically measured at indentation depths more than 200 nm, cannot be well correlated with the global mechanical behaviour of tested materials. Here, we study the H of the α phase in an additively manufactured titanium alloy using a nanoindentation mapping method with small indentation depths (< 200 nm). The results show that the α grains with various crystal orientations exhibit two groups of H values, different from a wide range of H values measured by conventional large-depth nanoindentation. The two groups of H values are attributed to a contribution of elasticity in the measurement of the H values using the small-depth nanoindentation. Furthermore, we correlate the H with the microscopic mechanical behaviour of α grains: With respect to the tensile direction, hard α grains are plastically deformed by shear banding and soft α grains are deformed by dislocation slip.

Creep analysis of cementitious materials in seawater using a poro-chemo-mechanical model

With the rapid growth of the offshore engineering sector, studying the durability of offshore structures becomes primordial. Evaluating experimentally the coupling between mechanical and chemical degradation of the cement-based materials and structures is a challenging task because it requires tracking the evolution of the micro-mechanisms associated with the degradation in real time for long periods. To tackle this issue, a numerical approach is proposed, based on the micromechanics and the coupling between a creep-damage model and a chemical model at the microstructural scale. The seawater chemical effect on cement paste is simulated by considering the penetration fronts of the aggressive water and the attack by layers in the material. The aim of this study is to provide a tool for the rapid mechanical evaluation of the offshore structures and therefore a tool that can be used for the optimization and the development of durable marine constructions. The results highlight the competition between protective and damaged layers formed due to seawater attack, and that the global mechanical behaviour strongly depends on the chemically modified phases in the cement paste.

Optimal designs of the multilevel chiral helical structures with local contact and fretting wear

The local contact characteristics of multilevel chiral helical structures are critical, which determines the fretting wear and further affects the service life. In this paper, a theoretical model including global mechanical behaviors, local contact, and fretting wear is established. The ratio of the axial total moment to force is utilized to describe the load bearing capacity. Two kinds of models are developed for contact forces: 1D-explicit and 2D-iteration model, which are verified by the finite element method (FEM). The 1D model provides the explicit expressions of contact forces, meanwhile, the 2D model possesses the high accuracy under the short pitch. Different kinds of contact forces and the fretting wear are solved by the multilevel contact transmission law and the Archard’s equation, respectively. Subsequently, the Pareto sets of multilevel chiral helical structures are obtained based on the theoretical model and the Non-dominated Sorting Genetic Algorithm-Ⅱ (NSGA-Ⅱ). Optimal designs with a strong load bearing capacity and a high fretting wear resistance are exhibited, which is useful to guide the design of multilevel chiral helical structures.

Integration of nanoindentation and finite element method for interpretable tensile properties: A cross-scale calculation method of uneven joints

Nanoindentation testing and its Reverse Analysis Method (RAM) show great potential in understanding the tensile properties of metallic alloys with various microstructures. Nevertheless, the tensile properties of heterogeneous materials such as nickel-based superalloy welded joints have not been well interpreted by combining the microstructures and nanoindentation results, due to their diverse and complex microscopic zones, which throws shade on the properties of separated zones in the material. Here we demonstrated a new method of implanting nanoindentation results into Finite Element Method (FEM) and applied the method to the welded joints with the zones of various microstructure features. The local properties are calculated by the nanoindentation data using RAM, and used as input of Finite Element (FE) simulation of an identical indentation process, to in turn verify the accuracy and reliability of the reverse model. The simulation results reveal that the global mechanical behaviors, such as Young's modulus, yield strength and strain hardening exponent, are related to the local properties to a great extent. Thus, the global properties can be verified by simulation straight after experiments, taking consideration of local properties and dimension parameters of different zones. It is shown that the maximum error between calculation of RAM and testing is within 5.1% in different zones, and the errors of maximum indentation depth and residual depth obtained by FE simulation are less than 2.4%, which indicates that the method provides a reliable prediction of mechanical properties of superalloy welded joints.

A novel multiple impact model for predicting the residual stress state

Developing ultrahigh-strength structural materials that are ductile, fracture resistant, and cost effective has been a long-standing desire for scientists and engineers. Surface nano-crystallization technology has recently been developed as one of the most effective methods to optimize surface structure, which can improve local and global mechanical behavior without compromising ductility. This technique involves the use of hundreds of small hard balls vibrated by high-power ultrasound so that they impact onto the surface of a material at high speed, also known as surface mechanical abrasion treatment (SMAT). Despite its success in enhancing the mechanical properties of steels and other structural materials, there is still lack of clear understanding of the relationships between desired surface structures/properties and controlling parameters in such surface treatment processes. Therefore, we calculated residual stress through computational modeling such as finite element analysis (FEA), and simulated the effect of all parameters during processing on residual compressive stress. Different multiple impact models are investigated to develop a more realistic model for the strengthening process.

FINITE ELEMENT ANALYSES FOR EUROPEAN MODEL OF THE STEEL AND FIBRE REINFORCED CONCRETE CIRCULAR HOLLOW SECTION COLUMN IN FIRE

AbstractThis paper is focuses on advanced numerical FEM model of the global mechanical behaviour of CHS columns with SFRC infill at elevated temperature description. The proposed model was validated on experimental data and examples from literature and it is a foundation for numerous of numerical simulations generation in aim to develop simplified design tool, which will follow the coming changes in European standard for composite member design in fire in EN1994‐1‐2:2020.

Experimental and two-scale numerical studies on the behavior of prestressed concrete-steel hybrid wind turbine tower models

Prestressed concrete-steel hybrid (PCSH) wind turbine tower has been recognized as an efficient alternative to traditional steel tube supporting towers for wind farms in harsh sites such as mountain regions. To investigate the global and local mechanical behavior including failure patterns of a full scale PCSH wind turbine towers, an experimental study on a substructure of a scaled PCSH tower is carried out firstly. Then, a material subroutine for three-dimensional (3D) fiber beam elements suitable for implicit analysis on the mechanical behavior of the substructure of the scaled PCSH tower is developed. A two-scale numerical model of the substructure of the scaled PCSH wind turbine tower employing the developed 3D fiber beam elements and solid elements is developed. The accuracy and efficiency of the developed two-scale numerical model for the behavior simulation of the substructure of the scaled PCSH wind turbine tower is illustrated by comparing the numerical results with the experimental measurements. Additional comparison of the simulation results using the developed two-scale numerical model is made with them of a model using sole 3D fiber beam elements and a model using sole solid elements, respectively. Results show that the force–displacement curve determined with the developed two-scale model is close to the test result and coincident well with that of the two models using 3D fiber beam elements and the solid elements. The developed two-scale model can describe the global behavior, the local failure patterns and the stress distribution of the tested specimen accurately with improved simulation efficiency. Finally, the validated two-scale modelling approach is employed to analyze the static behavior, modal parameter, and fatigue of the optimized full-scale PCSH wind turbine tower previously developed by the authors. The simulation results show that the two-scale model can reflect the stress of the PCSH wind turbine tower at the critical position as well as the global mechanical behavior with higher computational efficiency. The fiber beam model can be used for predicting only global, but not local, behavior.

The global mechanical response and local contact in multilevel helical structures under axial tension

Multilevel helical structures are widely applied in engineering and biological areas with complicated local contact of interwire and global mechanical behaviors. Based on the thin rod theory, we propose a theoretical model which can simultaneously calculate the global mechanical properties and the local contact behaviors of the multilevel helical structure. By considering the contact deformation and the periodic kinematic parameters (the curvatures and twist) of the high order helix, the quasi-static solution of the multilevel helical structure is derived under axial tension, and two types of contact forces including line and point are analyzed. The multilevel contact transmission law is proposed to reveal the relationship between the contact forces with different types and levels, and the tendency of two contact forces with pitch can be obtained. Compared with the Costello model, the deviation of global mechanical responses and finite element (FE) simulations is reduced for the high-level helical structure. The local contact forces from FE simulations are in agreement with the predictions of the present model. The effect of the structural parameters on the global mechanical responses as well as the local contact forces are analyzed according to the present model. Finally, based on an engineering practical cable, the global mechanical responses and local contact behaviors of the simplified cable structure are predicted under axial tension. This study contributes to the understanding of the transmission mode and mechanism of contact forces in the multilevel helical structure.