Structural Mechanics Research Articles

DESIGN AND ANALYSIS OF THE PISTON USING COMPOSITE MATERIALS LIKE AA7275 STRUCTURAL AND THERMAL ANALYSIS DONE IN ANSYS SOFTWARE

This project focuses on the design and analysis of a piston utilizing composite materials, particularly AA7275, to enhance structural integrity and thermal efficiency. The study employs ANSYS software to conduct comprehensive structural and thermal analyses. The structural analysis evaluates the mechanical behavior, stress distribution, and deformation characteristics of the piston under varying operating conditions. Meanwhile, the thermal analysis investigates the heat transfer mechanisms, temperature distribution, and thermal stress accumulation within the piston. By integrating composite materials and utilizing advanced simulation techniques, this project aims to optimize the performance and reliability of the piston, contributing to advancements in engine technology. ANSYS software facilitates Multiphysics simulations, allowing engineers to study the interactions between different physical phenomena such as structural mechanics, fluid dynamics, electromagnetics, and thermal effects. Its robust solvers and algorithms enable accurate prediction of system behavior under various operating conditions, helping engineers optimize performance, reliability, and efficiency. Moreover, ANSYS provides a range of specialized modules tailored to specific industries and applications, including automotive, aerospace, electronics, healthcare, and renewable energy. These modules incorporate domain-specific features and workflows, empowering engineers to address industry-specific challenges and design requirements effectively. Recent advancements in ANSYS software include enhanced computational capabilities, improved user interfaces, and integration with emerging technologies such as artificial intelligence and additive manufacturing. These developments enable engineers to accelerate the design iteration process, reduce time-to-market, and achieve superior product performance. Furthermore, ANSYS supports collaborative engineering workflows through its integration with product lifecycle management (PLM) and computer-aided design (CAD) software. This integration facilitates seamless data exchange between design, simulation, and manufacturing teams, ensuring consistency and accuracy throughout the product development lifecycle. KEY WORDS : AA7275; Piston; Structural integrity and Thermal Efficiency; Structural analysis; ANSYS; CAD.

A computational approach to modeling flow-induced large deformation of thin-walled compliant vessels

We present a computational method capable of modeling 3D flow-induced deformation of thin, highly compliant, hyperelastic vessels conveying viscous, inertial fluid. The method can uniformly consider vessel extension and collapse. Very large inflation, transient deformation, complex flow features as well as highly complex buckling shapes are well resolved by this method. The methodology combines finite volume and spectral methods for fluid motion, finite element method for structural mechanics of the vessel wall, and the immersed boundary method for two-way coupling between the wall and fluid. A hybrid of the continuous forcing and the ghost node methodologies capitalizing on the strengths of each is developed. The method avoids the surface instability encountered with the continuous forcing methods, as well as the need for domain remeshing as required in the iterative and partitioned approaches. The vessel wall can follow linear or nonlinear (strain softening and hardening) material models, and the fluid inertia can vary over a wide range. We demonstrate the versatility of the method by considering vessel inflation and collapse with large, complex, and transient deformation. Remarkable differences in vessel inflation at low versus moderate inertia are observed; this includes steady versus oscillatory motion, emergence of flow recirculation and pressure wave reflection which are well resolved. For the collapsing vessels, well-defined shapes with different buckling modes as well as highly complex buckling with fine surface folds are predicted. Additionally, a second-order correction to the well-known law of Laplace is developed and used to validate our computational results for vessel inflation.

Toward Fatigue-Tolerant Design of Additively Manufactured Strut-Based Lattice Metamaterials

Abstract The advent of additive manufacturing (AM) has enabled the prototyping of periodic and non-periodic metamaterials (a.k.a. lattice or cellular structures) that could be deployed in a variety of engineering applications where certain combinations of performance features are desirable. For example, these structures could be used in a variety of naval engineering applications where lightweight, large surface area, energy absorption, heat dissipation, and acoustic bandgap control are desirable. Furthermore, combining the multifunctional design optimization of these structures with progressive degradation due to cyclic loading could lead to fatigue-activated attritable systems with potentially tailorable performances not yet in reach by current conventional systems. Nevertheless, in order to deploy these complex geometry structures their multiphysics response has to be well understood and characterized. The objective of the current effort is to describe an initial approach for designing a uniaxial metamaterial specimen for fatigue testing as the first step toward the design of multi-axial fatigue test coupons. In order to compare bending- and stretching-dominated structures, two strut-based lattices made of Ti-6Al-4V alloy consisting of the octet and tetrakaidecahedron (or Kelvin) cells are examined. The specimens are designed to fail in the central area of the specimen where edge effects are minimized. Finite element results of the relevant structural mechanics are implemented and exercised to compare the performance of the eight relevant geometries and to evaluate the effect of relative density on fatigue life.

Spectral Properties of Mimetic Operators for Robust Fluid–Structure Interaction in the Design of Aircraft Wings

This paper presents a comprehensive study on the spectral properties of mimetic finite-difference operators and their application in the robust fluid–structure interaction (FSI) analysis of aircraft wings under uncertain operating conditions. By delving into the eigenvalue behavior of mimetic Laplacian operators and extending the analysis to stochastic settings, we develop a novel stochastic mimetic framework tailored for addressing uncertainties inherent in the fluid dynamics and structural mechanics of aircraft wings. The framework integrates random matrix theory with mimetic discretization methods, enabling the incorporation of uncertainties in fluid properties, structural parameters, and coupling conditions at the fluid–structure interface. Through spectral and localization analysis of the coupled stochastic mimetic operator, we assess the system’s stability, sensitivity to perturbations, and computational efficiency. Our results highlight the potential of the stochastic mimetic approach for enhancing reliability and robustness in the design of aircraft wings, paving the way for optimization algorithms that integrate uncertainties directly into the design process. Our findings reveal a significant impact of stochastic perturbations on the spectral radius and eigenfunction localization, indicating heightened system sensitivity. The introduction of randomized singular value decomposition (RSVD) within our framework not only enhances computational efficiency but also preserves accuracy in low-rank approximations, which is critical for handling large-scale systems. Moreover, Monte Carlo simulations validate the robustness of our stochastic mimetic framework, showcasing its efficacy in capturing the nuanced dynamics of FSI under uncertainty. This study contributes to the fields of numerical methods and aerospace engineering by offering a rigorous and scalable approach for conducting uncertainty-aware FSI analysis, which is crucial for the development of safer and more efficient aircraft.

Multi-criteria parametric optimization of the displacement and weight of a shell of minimal surface on a circular contour consisting of two inclined ellipses under thermal and power loading with consideration of geometric nonlinearity

Thin shells are well suited to optimal design problems, and the finite element method and gradient descent method make it possible to solve inverse problems in structural and applied mechanics. The calculation process takes into account geometric nonlinearity. In modern numerical studies, a formulation taking into account geometric nonlinearity in the finite element method is used, namely, a stepwise loading procedure. It becomes necessary to take into account the relations between displacement vectors and their derivatives and strain increments. These relations help to determine the stiffness matrix of the finite element at each loading step, which leads to a qualitative study of real displacements in the structure. The geometrically nonlinear calculation of a shell of minimum surface on a circular contour consisting of two inclined ellipses in a multi-criteria parametric optimization is performed by the finite element method. The finite element method is a universal variational method that is focused on solving the most complex problems of elasticity theory and applied and structural mechanics using separate calculation complexes. Stiffness matrix - for the whole body is formed on the basis of the finite element stiffness matrix. The system of solving equations of the finite element method is formed using the Lagrange's variational principle, according to which the total potential energy P of a finite element model of a body in a state of stability and equilibrium has a minimum value. As part of the sensitivity analysis, gradients of the design variables of the structure, displacements in the form of partial derivatives of these characteristics along the design variables, and shell thickness are calculated. The sensitivity information serves as the basis for building an optimal design algorithm using the gradient descent method of the objective function. Standard multi-criteria parametric optimization allows for an average of 10% steel savings, with geometric nonlinearity increasing to 20%. At this study site, 24.4% of sheet steel was saved, which is a significant relative saving. This methodology of the authors shows high results for innovative design and production of steel thin shells in Ukraine and around the world, and also makes it possible to apply several types of optimization to one research object.

Grain size-dependent delay of avalanches during void evolution in a nanocrystalline Ni

The effect of grain size on the underlying dynamics of void evolution in a nanocrystalline (NC) Ni was dissected. Multiscale characterizations reveal that, unlike the suppression of void nucleation by the compressive stress in coarse-grained Ni, dispersive nano- and micro-voids formed readily in NC Ni during compression. Acoustic emission measurements and molecular dynamic simulations demonstrate that the unique structural features and deformation mechanics implicitly occurring in NC metals play multifaceted roles during void evolution. Although the presence of excessive nucleation sites, such as grain boundaries and triple junctions, together with the activation of intergranular plasticity facilitate void nucleation, high interface population retards dislocation-driven void expansion, resulting in sluggish void growth and a corresponding delay of coalescence avalanches.

Research on the Impact of Non-Uniform and Frequency-Dependent Normal Contact Stiffness on the Vibrational Response of Plate Structures

Mechanical interfaces are prevalent in industries like aerospace and maritime, where the normal contact stiffness on these surfaces is a crucial component of the overall stiffness of mechanical structures. From the perspective of structural mechanics, normal contact stiffness significantly affects the dynamic response of mechanical structures and must be considered in mechanical design and simulation analysis. Essentially, the mechanical interface represents a typical type of nonlinear contact, characterized by both its non-uniform distribution and its frequency-dependent properties under external excitations. A plate structure was designed to study the distribution and frequency-dependent characteristics of normal contact stiffness on the mechanical interface. Experiments validated that the normal contact stiffness not only significantly increases the fundamental frequency of the plate but also alters its mode shapes. To replicate the experimental results in simulations, the BUSH elements were used to model the normal contact stiffness within the plate structure, arranging it non-uniformly and setting it to vary with frequency according to the plate’s mode shapes and frequency response. This method accurately replicated the plate’s mode shapes and response curves within the 0–1000 Hz range in simulations.

Enhancing Collaboration Between Transportation Education And Industry In Indonesia: A Cadet Perspective

This qualitative study investigates the perspectives of 50 cadets enrolled in Indonesian transportation institutes on collaboration between transportation education and industry. The research reveals a high perceived importance of industry-academia collaboration, highlighting its value in providing real-world experience and industry insights. However, challenges such as curriculum misalignment, limited practical training opportunities, and ineffective industry feedback mechanisms hinder effective collaboration. Recommendations include strengthening collaboration through internships and industry projects, regularly reviewing and updating curricula, expanding practical training opportunities, establishing structured industry feedback mechanisms, providing professional development for educators, and promoting lifelong learning. Implementing these recommendations can enhance collaboration, improve education programme relevance, and better prepare students for the transportation sector's demands. This research contributes to the development of a skilled workforce, driving the growth and competitiveness of the transportation industry in Indonesia.

NMR-based analysis of fractal characteristics of the pore structure of fully aeolian sand concrete under carbonation-dry-wet cycles

The evolution law of the pore structure of concrete is important for the study of concrete durability. To study the quantitative relationship between pore structure and macroscopic mechanics of aeolian sand concrete(ASC) under carbonation-dry-wet cycle(DWCs), the fractal characteristics of ASC under carbonation DWCs were analyzed by means of nuclear magnetic resonance(NMR) technology. The results showed that the carbonization product CaCO3 filled the pores and the compressive strength of ASC increased as the carbonization time increasing. When the DWCs was 0 times, the compressive strength of C1 and C2 groups increased by 9% and 13.6%, respectively, compared with C0. The compressive strength of C0 and C1 groups reached the maximum value when the DWCs was 40 times, while the C2 group reached the maximum value when the DWCs was 20 times. Compared with C0, the compressive strength of C1 and C2 increased by only 4% and 6%, respectively, after 100 DWCs. The fractal dimension Dmax reflected the proportion of harmless and multiple harmful pores in the damaged ASC. The fractal dimension Dmax was proportional to the proportion of harmless pores, and the correlation coefficient was 0.9303. The fractal dimension Dmax was inversely proportional to the proportion of harmful pores, and the correlation coefficient was 0.9565. The macroscopic mechanical properties were mainly affected by harmless pores and harmful pores, while the influence of less harmful pores and harmful pores was weak. This study will provide a theoretical justification for the use of ASC in practical engineering.

Femtosecond laser fabrication of 3D vertically aligned micro-pore network on thick-film Li4Ti5O12 electrode for high-performance lithium storage

The development of energy storage devices with high energy density relies heavily on thick film electrodes, but it is challenging due to the limited ion transport kinetics inherent in thick electrodes. Here, we report on the preparation of a directional vertical array of micro-porous transport networks on LTO electrodes using a femtosecond laser processing strategy, enabling directional ion rapid transport and achieving good electrochemical performance in thick film electrodes. Various three-dimensional (3D) vertically aligned micro-pore networks are innovatively designed, and the structure, kinetics characteristics, and electrochemical performance of the prepared ion transport channels are analyzed and discussed by multiple characterization and testing methods. Furthermore, the rational mechanisms of electrode performance improvement are studied experimentally and simulated from two aspects of structural mechanics and transmission kinetics. The ion diffusion coefficient, rate performance at 60 C, and electrode interface area of the laser-optimized 60-15% micro-porous transport network electrodes increase by 25.2 times, 2.2 times, and 2.15 times, respectively than those of untreated electrodes. Therefore, the preparation of 3D micro-porous transport networks by femtosecond laser on ultra-thick electrodes is a feasible way to develop high-energy batteries. In addition, the unique micro-porous transport network structure can be widely extended to design and explore other high-performance energy materials.

IN-MEMORY INTELLIGENT COMPUTING

Context. Processed big data has social significance for the development of society and industry. Intelligent processing of big data is a condition for creating a collective mind of a social group, company, state and the planet as a whole. At the same time, the economy of big data (Data Economy) takes first place in the evaluation of processing mechanisms, since two parameters are very important: speed of data processing and energy consumption. Therefore, mechanisms focused on parallel processing of large data within the data storage center will always be in demand on the IT market.
 Objective. The goal of the investigation is to increase the economy of big data (Data Economy) thanks to the analysis of data as truth table addresses for the identification of patterns of production functionalities based on the similarity-difference metric.
 Method. Intelligent computing architectures are proposed for managing cyber-social processes based on monitoring and analysis of big data. It is proposed to process big data as truth table addresses to solve the problems of identification, clustering, and classification of patterns of social and production processes. A family of automata is offered for the analysis of big data, such as addresses. The truth table is considered as a reasonable form of explicit data structures that have a useful constant – a standard address routing order. The goal of processing big data is to make it structured using a truth table for further identification before making actuator decisions. The truth table is considered as a mechanism for parallel structuring and packing of large data in its column to determine their similarity-difference and to equate data at the same addresses. Representation of data as addresses is associated with unitary encoding of patterns by binary vectors on the found universe of primitive data. The mechanism is focused on processorless data processing based on read-write transactions using in-memory computing technology with significant time and energy savings. The metric of truth table big data processing is parallelism, technological simplicity, and linear computational complexity. The price for such advantages is the exponential memory costs of storing explicit structured data.
 Results. Parallel algorithms of in-memory computing are proposed for economic mechanisms of transformation of large unstructured data, such as addresses, into useful structured data. An in-memory computing architecture with global feedback and an algorithm for matrix parallel processing of large data such as addresses are proposed. It includes a framework for matrix analysis of big data to determine the similarity between vectors that are input to the matrix sequencer. Vector data analysis is transformed into matrix computing for big data processing. The speed of the parallel algorithm for the analysis of big data on the MDV matrix of deductive vectors is linearly dependent on the number of bits of the input vectors or the power of the universe of primitives. A method of identifying patterns using key words has been developed. It is characterized by the use of unitary coded data components for the synthesis of the truth table of the business process. This allows you to use read-write transactions for parallel processing of large data such as addresses.
 Conclusions. The scientific novelty consists in the development of the following innovative solutions: 1) a new vector-matrix technology for parallel processing of large data, such as addresses, is proposed, characterized by the use of read-write transactions on matrix memory without the use of processor logic; 2) an in-memory computing architecture with global feedback and an algorithm for matrix parallel processing of large data such as addresses are proposed; 3) a method of identifying patterns using keywords is proposed, which is characterized by the use of unitary coded data components for the synthesis of the truth table of the business process, which makes it possible to use the read-write transaction for parallel processing of large data such as addresses. The practical significance of the study is that any task of artificial intelligence (similarity-difference, classification-clustering and recognition, pattern identification) can be solved technologically simply and efficiently with the help of a truth table (or its derivatives) and unitarily coded big data . Research prospects are related to the implementation of this digital modeling technology devices on the EDA market. KEYWORDS: Intelligent

First and second law analysis of crack propagation in canvas painting

The knowledge of how the craquelures happen and their pattern on historical objects, especially paintings, is interested in the field of cultural heritage. Entropy generation and thermal analysis of crack growth are calculated numerically for the canvas painting. The painting is modeled as a three-layer composite with isotropic material properties. An in-house code is developed to model the plane strain elasto-static structural mechanics with hybrid-Trefftz finite element formulation. The results are benchmarked with numerical and analytical solutions. Entropy generation and temperature fields are simulated throughout stacking in mode I of a delamination process. The parameter study shows that the parameter of entropy has a great influence on the process of expectation of break proliferation in fast and low areas. It is likewise demonstrated that the use of the corruption entropy age hypothesis gives a technique for assessing the steady in the law of crack growth regarding the rate of entropy production.

Comparative Study of Static and Dynamic Analysis of Multistoried Building

In a moderate seismic activity, relying solely on the static force method to estimate the seismic force assessing the vulnerability and behaviour of RCC buildings under seismic loads is insufficient. The seismic response of the building system is highly influenced by the analysis method adopted. In the past years, static approaches were preferred due to their simplicity, although these methods provided safe design, they may have been overly cautious. Dynamic analysis, on the other hand, is a fundamental aspect of structural mechanics, that describes and predicts the behaviour of structures subjected to dynamic loads. Dynamic load includes wind, imposed load, earthquake, etc. Dynamic analysis techniques, such as modal analysis, time history analysis, and dynamic displacement analysis. RCC structures are mainly designed to resist static load. This process of ignoring dynamic events sometimes becomes the cause of disasters, especially in the case of earthquakes. This research paper provides information on the comparison of various parameters in static and dynamic analysis. Two RCC multistoried residential buildings (g+10 and g+25) acting on seismic zone IV are analyzed using the static analysis method and response spectrum method with ETABS 16. The research investigates the effect on various structural parameters such as story displacement, story drift, and support reactions. The results are compared and evaluated to assess the performance of the response spectrum method over the static analysis method.

ЭНЕРГЕТИЧЕСКИЕ СВОЙСТВА СИММЕТРИЧНЫХ ДЕФОРМИРУЕМЫХ СИСТЕМ

Energy methods for calculating structures, which have become popular for a century, are based on the Lagrange principle and have the meaning of equality of work of external forces and internal forces. Having proved their effectiveness in the overwhelming majority of problems of structural mechanics, they became the dominant approach in formulating the problems of studying solid deformable systems and gave rise to the main methodology for solving problems. As a result, a situation has arisen that the internal potential energy of a deformed body remains insufficiently studied.
 The paper develops an approach to the study of the symmetric structure at critical levels of strain energy. The criterion of critical levels of strain energy, based on the concepts of "self-stress" ("self-balance") of a deformable body. Limiting values of the structure strain energy may get by varying the reactions and deflections in the nodal points. The extreme values of forces and displacements of the rods are calculated in matrix form from the values of nodal reactions (displacements).
 Methodology for studying the energy properties of a system is shown on the examples of the study of symmetric rod systems without involving the concept of external forces. The technique is based on matrix methods of structural mechanics and the mathematical apparatus of eigenvalue problems. The comparison of structural design and structural analysis solution of structural mechanics tasks by traditional methods and with the proposed methodology is carried out.

Latent Crossover for Data-Driven Multifidelity Topology Design

Abstract Topology optimization is one of the most flexible structural optimization methodologies. However, in exchange for its high level of design freedom, typical topology optimization cannot avoid multimodality, where multiple local optima exist. This study focuses on developing a gradient-free topology optimization framework to avoid being trapped in undesirable local optima. Its core is a data-driven multifidelity topology design (MFTD) method, in which the design candidates generated by solving low-fidelity topology optimization problems are updated through a deep generative model and high-fidelity evaluation. As its key component, the deep generative model compresses the original data into a low-dimensional manifold, i.e., the latent space, and randomly arranges new design candidates over the space. Although the original framework is gradient free, its randomness may lead to convergence variability and premature convergence. Inspired by a popular crossover operation of evolutionary algorithms (EAs), this study merges the data-driven MFTD framework and proposes a new crossover operation called latent crossover. We apply the proposed method to a maximum stress minimization problem in 2D structural mechanics. The results demonstrate that the latent crossover improves convergence stability compared to the original data-driven MFTD method. Furthermore, the optimized designs exhibit performance comparable to or better than that in conventional gradient-based topology optimization using the P-norm measure.

Bioinspired Interfacial Friction Control: From Chemistry to Structures to Mechanics.

Organisms in nature have evolved a variety of surfaces with different tribological properties to adapt to the environment. By studying, understanding, and summarizing the friction and lubrication regulation phenomena of typical surfaces in nature, researchers have proposed various biomimetic friction regulation theories and methods to guide the development of new lubrication materials and lubrication systems. The design strategies for biomimetic friction/lubrication materials and systems mainly include the chemistry, surface structure, and mechanics. With the deepening understanding of the mechanism of biomimetic lubrication and the increasing application requirements, the design strategy of multi-strategy coupling has gradually become the center of attention for researchers. This paper focuses on the interfacial chemistry, surface structure, and surface mechanics of a single regulatory strategy and multi-strategy coupling approach. Based on the common biological friction regulation mechanism in nature, this paper reviews the research progress on biomimetic friction/lubrication materials in recent years, discusses and analyzes the single and coupled design strategies as well as their advantages and disadvantages, and describes the design concepts, working mechanisms, application prospects, and current problems of such materials. Finally, the development direction of biomimetic friction lubrication materials is prospected.

Research on Topology Optimization Design of Truss Structure

Due to continuous advances in engineering technology and architecture, the use of truss structures is expanding. The design method of ideal truss structure is the main research topic of this paper. The topology optimization method is applied to a bridge design case study. The load and total material utilization ratio of each rod of triangular truss, arch truss and Pratt truss were determined by using structural mechanics solver. By comparing the stress and material consumption of the truss structure, it shows that the truss structure has advantages in stress and can be used in the truss construction of short-distance arch bridge. Truss is the basic unit of the topology optimization method of truss structure proposed in this study. By optimizing the topological shape of the truss, the ideal design of the whole structure is realized. While maintaining structural stiffness and stability, the technology can significantly reduce the weight and cost of the structure.

Research on Economic Optimization Scheme of Pratt Truss Bridge

Economy is an important factor in bridge construction. The economic optimization of truss bridge is of great significance to improving the economic benefit of bridge construction. However, the safety and stability in bridge construction are often valued in traditional truss Bridges, and its economy is often ignored. The purpose of this paper is to study the economic optimization of Pratt truss bridge with 120 m span, 8m and node length of 6m, 10m and 12m respectively. The study of establishing two-dimensional model using structural mechanics solver shows that when the total length of the Pratt truss node is 12m, the total volume of the truss is the smallest, that is, the least materials are used, and the linear relationship between the bridge span and the node length is established to a certain extent. The results of this study provide an effective reference for the economic optimization of similar truss bridge structures.

Numerical simulation of the dynamic problem of a generalized system with distributed parameters

Introduction. Questions of mathematical modeling of the dynamic problem in the form of a generalized system with one degree of freedom are discussed. Such systems include high-rise tower-type structures. Seismic stability of unique tower-type objects represents a relevant research problem.Aim. To determine the stress-strain state of a studied object under the action of external factors in the form of an earthquake accelerogram.Materials and methods. The methods of structural mechanics, dynamics of structures, and numerical simulation were used. The Lagrange equation was used as a basis for obtaining the motion equation of a generalized system with distributed parameters. The research methodology also included mathematical modeling of the considered systems, their numerical analysis, comparison of the obtained results with literature data.Results. A mathematical model was developed to investigate the stress-strain state of engineering structures under various external, including seismic, effects. The differential equation of the generalized system is solved directly using the method of successive approximations and the Duhamel integral at each time step. The developed algorithm was used to compile a software application in the FORTRAN language followed by obtaining the kinematic and static data of the investigated object. Using the example of a tower-type structure, free vibrations from the action of an instantaneous impulse were investigated. The results from a given earthquake accelerogram are presented.Conclusions. The results obtained on the free vibrations of the object under study agree well with those obtained by numerical simulation. The results obtained by numerical differentiation are effectively identical with those obtained by numerical integration, under the action of various effects. The validity of the results is confirmed by comparing the results obtained by the two methods. The developed software applications can be used for monitoring the state of unique tower-type objects.

Viscoelasticity of hydrating shotcrete as key to realistic tunnel shell stress assessment with the New Austrian Tunneling Method

The New Austrian Tunneling Method (NATM) essentially rests on observational information concerning displacements measured in selected positions at the inner surface of shotcrete tunnel shells. The combination of these measurements with advanced material and structural mechanics, in the course of so-called hybrid methods, have successfully delivered, for more than 20 years, practically relevant estimations of internal and external forces and corresponding degrees of utilization. The reliability of the latter, however, may crucially depend on the used material model. Based on a recently proposed analytical structural mechanics model [Acta Mech 233, 2989–3019 (2022)], and focusing on the benchmark example of measurement cross section MC1452 of the Sieberg tunnel, driven in the 1990s in Miocene clay marl, the present paper compares the estimations of forces and degrees of utilization arising from differently refined constitutive concepts, namely (i) aging elasticity, (ii) aging linear viscoelasticity, and (iii) aging nonlinear viscoelasticity. It turns out that only the consideration of aging nonlinear viscoelastic material behavior provides access to realistic values for the degree of utilization, being lower than one. Simpler material models would indicate local material failure, which was not observed in situ.