A novel strain-based finite element family for mesh-independent analysis of the tensile failure of reinforced concrete bars

The paper presents a novel family of strain-based beam finite elements (FE) for analysis of tensile failure of a reinforced concrete bar (RC bar), with results of the analysis being independent of the applied FE mesh. The composite bar consists of a continuous longitudinal ductile reinforcing bar(s) surrounded by brittle concrete cover, which are considered separately in the model. Longitudinal slip at the contact between the concrete cover and reinforcing bars is allowed, while their relative displacements perpendicular to the axis of the RC bar are prevented. Cracks in concrete cover occur when tensile stress in concrete exceeds its tensile strength. Propagation of partially connected crack, that is, softening of the material at the crack, is described through constitutive law in form of nonlinear relationship between stresses in concrete at the crack and the width of the crack. Each separate crack is considered discretely as a discontinuity in geometry of the element. In the analysis of cracking of concrete, it is commonly assumed that the discrete crack can occur at the nodes of FE only. However, this assumption leads to dependence of the analysis results on the employed FE mesh. The presented family of FE enables occurrence of the crack anywhere along the FE. In order to achieve this, the discrete crack is excluded from equations of FE and additional boundary conditions are introduced at the discontinuity. This approach ensures that the location of the cracks, their number and their propagation are independent of the applied FE mesh. Advantages of the novel family of FE are thoroughly presented in a parametric study which investigates influence of number of FE as well as influence of degrees of interpolation and integration on the cracking of RC bar under tensile loading. Experimental results of tensile tests on the analysed bar are available in literature. It can be concluded that the results obtained with the minimal possible number of novel FE and sufficiently high degree of numerical integration scheme, applied for solving integrals in equations of FE, are considerably more accurate than the results of previous analyses with model of discrete crack at the nodes of FE only.

Enhancement of Anti-locking Brake System Performance by using Intelligent Control Technique with Different Road Conditions

Recently, the vehicle brake system equipped with anti-lock braking systems (ABS) is considered one of the most important effective safety systems. The importance of ABS, to get maintains the safety of vehicles on roads during emergency braking and it enables reliable stopping whilst maintaining the vehicle stability and ease steer-ability. Therefore, the aim of this research is to investigate the vehicle braking performance of controlled brake ABS that is designed with three types of controller and compares them, they are bang-bang, Proportional Integral Derivative (PID) and Fuzzy Logic Control (FLC) on rough dry and wet roads to control longitudinal slip. The main obstacles of controller design in automobile systems are concerned to high non-linearities of the mathematical model. 2DOF longitudinal quarter vehicle model with taking into account the rational motion of the tire is used to examine the braking performance. The tire-road interface model and braking system model are included in vehicle model. By reviewing the results, it was found that FLC method has an effective and better effect compared to two methods on the performance of brake system equipped with ABS system. It was found that vehicle stopping distance was reduced by 21.77m and 10.3m with dry and wet asphalt roads respectively compared to braking without ABS for fuzzy control at velocity 100 km/hr.

Comparison of Nonlinear Receding-Horizon and Extended Kalman Filter Strategies for Ground Vehicles Longitudinal Slip Estimation

Friction efforts are present in almost all mechanical applications, due to contact between bodies and there are many important situations, in which they must be properly controlled. Among these, there are tire contact forces, which is focus of many studies in autonomous vehicles and control applications on vehicle systems, since the tire forces and moments are nonlinear and may be modelled as friction efforts. Any control synthesis focused to optimize its performance must be associated to state estimators, since the efforts depend on slip variables, as longitudinal slip and sideslip angle, and it is not possible to accurately measure them. So, in this paper, two state estimation algorithms are evaluated: Extended Kalman Filter (EKF) and Moving Horizon State Estimation (MHSE), which are applied to a quarter-car model for longitudinal dynamics. It is presented that, for both traction and braking phases, the MHSE is more accurate, since it takes explicitly into account the nonlinear model in the estimation process, independently of Jacobian sensitivities to discontinuities as is the case here. So, it is demonstrated that the developed estimator may be successfully associated to controllers with the objective of optimize tire performance in traction and braking control.

Performance Review of Three Car Integrated ABS Types: Development of a Tire Independent Wheel Speed Control

This study concerns the development and testing of three types of Anti-lock Brake Systems (ABS): a standard on-off wheel’s acceleration control; a wheel’s longitudinal slip controller based on a discrete Proportional-Integral-Derivative (PID) control; and a novel type of ABS that involves controlling the wheel’s speed through a discrete PID. This work was developed inside a wider project that will lead to the implementation of stability control systems in a prototype car. For this reason, the typologies of ABS must not require extra sensors compared to those in standard vehicles: Inertial Measurement Unit (IMU) and 4-wheel speed sensors. Furthermore, they must be easily integrated with other controls and electronic components in terms of sampling time and values. The standard ABS seems more appropriate than the others two because it uses only parameters defined by sensors and it has a simple architecture that does not have the problem of computational time. However, in recent years, cars have been equipped with Electro-Hydraulic-Braking (EHB) units that improve the performance of the system controls. In fact, it is possible to use a control that allows actuators to follow a continuous target and smooth out pressure actions. Even if the longitudinal Slip Controller has a simple architecture and uses a PID control, it is limited to using quantities estimated instead of measured: the tires’ friction coefficient, the tires’ longitudinal stiffness, and the car’s speed. Therefore, the use of a Wheel Speed Controller is the right compromise to link the advantages of both controllers by following the braking pressure continuously and not needing to know the condition and properties of the tires. The results of tests carried out in a Hardware-In-the-Loop (HiL) system are showed and involved a complex vehicle model implemented in real-time.

Sequential Track–Bridge Interaction Analysis of Quick-Hardening Track on Bridge Considering Interlayer Friction

A quick-hardening track (QHT) was developed by injecting quick-hardening mortar into an existing ballast track to rapidly substitute the ballast track with a slab track, thereby improving maintainability and running safety. QHT tracks on a bridge undergo track–bridge interactions similar to other track systems. This paper presents a model to analyze the interaction between the QHT and the bridge. This model considers the longitudinal resistances of rail fasteners and anchors, as well as the interlayer friction between the track and the bridge. A sequential analysis method was applied to systematically consider such effects, revealing that rail additional stress will be high if the track slips over the bridge for a very low frictional coefficient of 0.1. Furthermore, a track segment without an anchor can slip under train traction load when the frictional coefficient is 0.3 or lower. For low friction cases, low-speed operation is advised to prevent the accumulation of the resulting longitudinal slip displacements of the track. An anchor should be installed immediately after the quick-hardening mortar provides sufficient bearing strength to the anchors. The proposed sequential analysis is useful for determining the critical friction coefficient and appropriate longitudinal resistance of a rail fastener, as well as for verifying track safety.

Design of slip-based traction control system for EV and validation using co-simulation between Adams and Matlab/Simulink

This paper focuses on controlling traction for a four-wheel electric vehicle by using the longitudinal slip ratio control technique. By keeping the slip ratio value inside an optimal limit, it can be ensured that the maximum driving force is obtainable by increasing the friction force between tire and road. The usefulness of the sliding mode control method is to provide robust performance from the parameter uncertainties at different road conditions. A control law is formulated based upon the Lyapunov stability approach to assure the sliding action. To satisfy the robustness, a vehicle model is made in Matlab, and it is simulated based on various parameter values. The slip ratios at different parameter values are plotted for open loop and closed loop. Then considering the vehicle kinematics and dynamics, a 3D CAD model using Catia is developed. Then exporting the model to Adams to use it as a plant model for the vehicle, co-simulation has been achieved by keeping the slip-based traction controller in Matlab/Simulink. Matlab/Simulink and Adams/View simulation validate the proposed method.

Dynamic modeling and experimental validation of skid-steered wheeled vehicles with low-pressure pneumatic tires on soft terrain

Wheeled skid-steered technology has an increasing interest in its use for off-road unmanned ground vehicles, because of its great mobility and compact mechanical structure. By integrating multibody dynamics model and semi-empirical tire-terrain model, this paper presents a dynamic modeling approach for skid-steered wheeled vehicles with low-pressure pneumatic tires on soft terrain to predict and investigate its steering performance. The forward dynamics equations are built by spatial vector algebra. The tire–terrain model estimates flexible deformation and sinkage of the tire, and calculates forces and torques exerted on the tire according to relative motions of tire–terrain contact. The combined longitudinal slip and lateral skid of tires, and the vertical coupled deformations of tires and terrain are also considered in tire-terrain model. This approach optimizes the solution procedure and improves the computing efficiency. The simulation results show that the proposed tire–terrain model can predict the effects of rigid and flexible operation modes of tires on mechanical properties of tires and steering performances of the vehicle. The proposed dynamic model is validated on a six-wheeled skid-steered vehicle. The comparisons between experimental results and simulations show that the proposed dynamic model provides a better accuracy of steering performance simulation for skid-steered vehicles.