Ilinca Stanciulescu

Simulation of tyre–pavement interaction for predicting contact stresses at static and various rolling conditions

This paper describes the development of a 3D tyre–pavement interaction model to predict the tyre–pavement contact stress distributions for future use in the mechanistic analysis of pavement responses. The ribbed radial-ply tyre was modelled as a composite structure (rubber and reinforcement), and the tyre material parameters were calibrated through load-deflection curves. The steady-state tyre rolling process was simulated using an arbitrary Lagrangian Eulerian formulation. The model results are consistent with previous measurements and validate the existence of non-uniform vertical contact stresses and localised tangential contact stresses. The analysis results show that the non-uniformity of vertical contact stresses decreases as the load increases, but increases as the inflation pressure increases. However, vehicle manoeuvring behaviour significantly affects the tyre–pavement contact stress distributions. For example, tyre braking/acceleration induces significant longitudinal contact stresses, while tyre cornering causes the peak contact stresses shifting towards one side of the contact patch. The model results provide valuable insights into understanding the realistic tyre–pavement interaction for analysing pavement responses at critical loading conditions.

Effect of Surface Friction on Tire–Pavement Contact Stresses during Vehicle Maneuvering

AbstractAccurate modeling of tire–pavement contact behavior plays an important role in the analysis of pavement performance and vehicle stability control. A three-dimensional (3D) tire–pavement interaction model was developed using the FEM to analyze the forces and contact stresses generated during vehicle maneuvering (free rolling, braking/acceleration, and cornering). A pneumatic radial-ply tire structure with rubber and reinforcement was simulated. The steady-state, tire-rolling process was simulated using an Arbitrary Lagrangian Eulerian (ALE) formulation. An improved friction model that considers the effect of sliding speed on friction coefficients was implemented to analyze the effects of pavement surface friction on contact stresses, friction forces, and cornering forces. The results showed that the magnitudes and nonuniformity of contact stresses are affected by vehicle-maneuvering conditions. As the pavement surface friction increases, the tangential tire–pavement contact stresses at various roll...

Characterizing Dynamic Transitions Associated With Snap-Through: A Discrete System

Geometrically nonlinear structures often possess multiple equilibrium configurations. Under extreme conditions of excitation it is possible for these structures to exhibit oscillations about and between these co-existing configurations. This behavior may have serious implications for fatigue in the context of aircraft surface panels. Snap-through is a name often given to sudden changes in dynamic behavior associated with mechanical instability (buckling). This is an often encountered problem in hypersonic vehicles in which severe thermal loading and acoustic excitation conspire to create an especially hostile environment for structural elements. In this paper, a simple link model is used, experimentally and numerically, to investigate the mechanisms of snap-through buckling from a phenomenological standpoint.

Can complex systems really be simulated

The simulation of complex systems is important in many fields of science and in real-world applications. Such systems are composed of many interacting subsystems. There might exist different software packages for simulating the individual subsystems and co-simulation refers to the simultaneous execution of multiple interacting subsystem simulators. Simulation or co-simulation, if not designed properly, can return misleading numerical solutions (unstable numerical solutions for what is in fact a stable system or vice versa). To understand the cause of these numerical artifacts, we first propose a simple mathematical model for co-simulation, and then construct stability charts. These charts shed light on transitions between stable and unstable behavior in co-simulation. Our goal is to understand the stability properties of the simulated and co-simulated representation of the continuous system. We will achieve this goal by expressing the trace and determinant of the discretized system in terms of the trace and determinant of the continuous system to establish stability criteria.

Numerical simulation of fibrous biomaterials with randomly distributed fiber network structure

This paper presents a computational framework to simulate the mechanical behavior of fibrous biomaterials with randomly distributed fiber networks. A random walk algorithm is implemented to generate the synthetic fiber network in 2D used in simulations. The embedded fiber approach is then adopted to model the fibers as embedded truss elements in the ground matrix, which is essentially equivalent to the affine fiber kinematics. The fiber–matrix interaction is partially considered in the sense that the two material components deform together, but no relative movement is considered. A variational approach is carried out to derive the element residual and stiffness matrices for finite element method (FEM), in which material and geometric nonlinearities are both included. Using a data structure proposed to record the network geometric information, the fiber network is directly incorporated into the FEM simulation without significantly increasing the computational cost. A mesh sensitivity analysis is conducted to show the influence of mesh size on various simulation results. The proposed method can be easily combined with Monte Carlo (MC) simulations to include the influence of the stochastic nature of the network and capture the material behavior in an average sense. The computational framework proposed in this work goes midway between homogenizing the fiber network into the surrounding matrix and accounting for the fully coupled fiber–matrix interaction at the segment length scale, and can be used to study the connection between the microscopic structure and the macro-mechanical behavior of fibrous biomaterials with a reasonable computational cost.

A co-simulation environment for high-fidelity virtual prototyping of vehicle systems

Computer simulation is being increasingly used for virtual prototyping of ground vehicles ahead of building actual hardware prototypes. This paper describes a methodology to co-simulate, with high fidelity and in one computational framework, all of the main vehicle subsystems for improved engineering design. The approach leverages the capabilities of three software packages (ADAMS, PSAT, FTire) to simulate vehicle kinematics/dynamics, powertrain dynamics, and tyre-terrain contact in one unified environment. As a result, information about forces in vehicle components, driver comfort, maximum cornering speed, fuel efficiency and engine emission details can all be obtained at the same time. This data is relevant when used for comparing competing designs that draw on different values of vehicle parameters (inertia, material, suspension properties, stiffness), powertrain system settings for conventional, hybrid, or fuel cell topologies, and tyre-terrain interface parameters (road profile, tyre pressure, tread). A generic sedan and US army’s high mobility multipurpose wheeled vehicle (HMMWV), both with conventional powertrain systems, are used to demonstrate the proposed simulation framework.

Inverse computation of cohesive fracture properties from displacement fields

The cohesive zone model (CZM) is a key technique for finite element (FE) simulation of fracture of quasi-brittle materials; yet its constitutive relationship is usually determined empirically from global measurements. A more convincing way to obtain the cohesive relation is to experimentally determine the relation between crack separation and crack surface traction. Recent developments in experimental mechanics such as photoelasticity and digital image correlation (DIC) enable accurate measurement of whole-field surface displacement. The cohesive stress at the crack surface cannot be measured directly, but may be determined indirectly through the displacement field near the crack surface. An inverse problem thereby is formulated in order to extract the cohesive relation by fully utilizing the measured displacement field. As the focus in this article is to develop a framework to solve the inverse problem effectively, synthetic displacement field data obtained from finite element analysis (FEA) are used. First, by assuming the cohesive relation with a few governing parameters, a direct problem is solved to obtain the complete synthetic displacement field at certain loading levels. The computed displacement field is then assumed known, while the cohesive relation is solved in the inverse problem through the unconstrained, derivative-free Nelder–Mead (N–M) optimization method. Linear and cubic splines with an arbitrary number of control points are used to represent the shape of the CZM. The unconstrained nature of N–M method and the physical validity of the CZM shape are guaranteed by introducing barrier terms. Comprehensive numerical tests are carried out to investigate the sensitivity of the inverse procedure to experimental errors. The results show that even at a high level of experimental error, the computed CZM is still well estimated, which demonstrates the practical usefulness of the proposed method. The technique introduced in this work can be generalized to compute other internal or boundary stresses from the whole displacement field using the FE method.

Vibration and large deflection of cantilevered elastica compressed by angled cable

A thin cantilevered beam is compressed by a cable attached to the tip of the beam and terminating near the base. Large-deflection equilibrium configurations and small vibrations about equilibrium are investigated. This system has a direct application to solar-sail structures, where the structural booms could be designed to bend to supply tension loading in the sail membrane. The equilibrium and vibration properties are examined in three ways: numerical integration of the governing elastica equations using a shooting method, finite element analysis using ABAQUS, and experiments with a polycarbonate strip bent by a cable that is tightened with a turnbuckle. Equilibrium shapes and vibration mode shapes and frequencies are obtained for two different cable attachment points offset slightly from the beams base in the axial and transverse directions. Frequencies obtained from a three-dimensional finite element analysis are also presented.

On Snap-Through Buckling

Snap-through buckling can reduce the life-span of structural systems such as aircraft surface paneling. This is envisioned to be a specific problem in hypersonic vehicles in which severe thermal loading and acoustic excitation conspire to create an especially hostile environment for structural elements. A shallow arch, and two simplified link models are used to investigate the mechanisms of snap-through buckling from a fundamental, or phenomenological, standpoint. The complexities introduced by modal interactions are introduced and a method for identifying snap-through buckling is developed.

A PARALLEL GPU IMPLEMENTATION OF THE ABSOLUTE NODAL COORDINATE FORMULATION WITH A FRICTIONAL/CONTACT MODEL FOR THE SIMULATION OF LARGE FLEXIBLE BODY SYSTEMS

This contribution discusses how a flexible body formalism, specifically, the Absolute Nodal Coordinate Formulation (ANCF), is combined with a frictional/contact model using the Discrete Element Method (DEM) to address many-body dynamics problems; i.e., problems with hundreds of thousands of rigid and deformable bodies. Since the computational effort associated with these problems is significant, the analytical framework is implemented to leverage the computational power available on today’s commodity Graphical Processing Unit (GPU) cards. The code developed is validated against ANSYS and FEAP results. The resulting simulation capability is demonstrated in conjunction with hair simulation. THEORETICAL BACKGROUND - ANCF For almost a decade the Absolute Nodal Coordinate formulation (ANCF) has been widely used to carry out the dynamics analysis of flexible bodies that undergo large rotation and large deformation. This formulation is consistent with the nonlinear theory of continuum mechanics and easy to implement. Also, it leads to a constant mass matrix which makes it computationally more efficient compared to other nonlinear finite element formulations.