Search Results

This paper proposes a vehicle performance/safety method using combined active steering and differential braking to achieve yaw stability and rollover avoidance. The advantages and disadvantages of active steering and differential braking control methods are identified under a variety of input signals, such as J-turn, sinusoidal, and fishhook inputs by using the implemented linear 4 DOF model. Also, the nonlinear model of the vehicle is evaluated and verified through individual and integrated controller. Each controller gives the correction steering angle and correction moment to the simplified steering and braking actuators. The integrated active steering and differential braking control are shown to be most efficient in achieving yaw stability and rollover avoidance, while active steering and differential braking control has been shown to improve the vehicle performance and safety only in yaw stability and rollover avoidance, respectively.

Aircraft wing geometry morphing is a technology that has seen recent interest due to demand for aircraft to improve aerodynamic performance for fuel saving. One proposed idea to alter wing geometry is by a modular morphing wing designed through a discretization method and constructed using variable geometry truss mechanisms (VGTM). For each morphing maneuver, there are sixteen possible actuation paths for each VGTM module. This paper proposes a method to find an optimal actuation path from the point of view of the longitudinal static stability. To do so, we locate the aerodynamic center (ac) and the center of gravity (cg) of each VGTM module which is first determined according to its morphed shape. Then, the ac and cg of the entire modular morphing wing can be determined and the stability margin can be computed. The two suggested methods to obtaining the ac for each VGTM module are the integration method and the geometry method.

The development of an optimized heat treatment schedule, with the aim of maximizing strength and relieving tensile residual stress, is important to prevent in-service cylinder distortion in Al alloy engine blocks containing cast-in gray iron liners. However, to effectively optimize the engine block heat treatment schedule, the current solutionizing parameters must be analyzed and compared to the as-cast condition to establish a baseline for residual stress relief. In this study, neutron diffraction was carried out to measure the residual stress along the aluminum cylinder bridge following solution heat treatment. The stresses were measured in the hoop, radial and axial orientations and compared to a previous measured as-cast (TSR) engine block. The results suggest that solution heat treatment using the current production parameters partially relieved tensile residual stress in the Al cylinder bridge, with stress relief being more effective near the bottom of the cylinder.

Development of lightweight alloys suitable for automobile applications has been of great importance to the automotive industry in recent years. The use of 319 type aluminum alloy in the production of gasoline engine blocks is an example of this shift towards light alloys for large automobile components. However, excessive residual stress along the cylinder bores of these engine blocks may cause problems during engine operation. Therefore, in this study, neutron diffraction was used to evaluate residual stresses along the aluminum cylinder bridge and the gray cast iron liners. The strains were measured in the hoop, radial, and axial orientations, while stresses were subsequently calculated using generalized Hooke's law. The results suggest that the residual stress magnitude for the aluminum cylinder bridge was tensile for all three measured components and gradually increased with cylinder depth towards the bottom of the cylinder.

The major disadvantage of powder metallurgy (PM) is the density gradient throughout the green powder compacts. During the compaction process, due to the existence of friction at powder-tool interfaces, the contact surfaces experience a non-uniform stress distribution having to do with variable friction coefficient and tool kinematics, consequently resulting in density gradient throughout the powder compacts. This represents a serious problem in terms of the reliability and performance of a final product, as the density gradient may contribute to a crack-defect generation during the compaction cycle, and more importantly a non-uniform compact shrinkage during the sintering process. Simulation analyses were conducted using the finite element software, MSC.Marc Mentat, and Shima and Oyane powder constitutive model, to study and suppress the causes of density gradient in the cylindrically shaped green powder compacts.

The uniaxial compression test was used to assess the influence of strain amount on the behavior of precipitates and texture of the Al-7%Si-1%Cu-0.5%Mg alloy, modified with micro-additions of V, Zr and Ti. As revealed through metallographic examinations, fracturing and re-orientation of the second-phase particles increased with increasing compression strain. However, the intermetallic particles experienced substantially more frequent cracking than the eutectic silicon. The crystallographic texture was measured and correlated with deformation behavior of the alloy. The weak texture of 11<211> and 111<110> components, detected after casting transformed to a mixture of 1<110>, 112<110> and 111<110> components after room-temperature compression deformation. The intensity of the texture components depended on the strain amount. It is concluded that the texture formation in the studied alloy is controlled by the precipitates formed during solidification of the alloy.

Aluminum alloys have been replacing ferrous alloys in automotive applications to reduce the weight of vehicles. The engine block is a striking example of weight reduction, and is made of Al-Si-Cu-Mg (319 type) alloys. The wear resistance in the engine block is enabled by cast iron liners, and these liners introduce tensile residual stress due to a thermo-mechanical mismatch. Typically, an artificial aging treatment effectively reduces residual stress. In this study, neutron diffraction was used to measure the residual stress profiles along the cylinder bridge of a T5 treated 319 aluminum alloy engine block. Results indicated high tensile residual stresses (200-300 MPa) in the hoop and axial orientation at depths of 50-60 mm below the head deck. The high residual stresses were likely due to a combination of minimal stress relief during artificial aging and stress development during post process cooling.

Continuous efforts to develop a lightweight alloy suitable for the most demanding applications in automotive industry resulted in a number of advanced aluminum (Al) and magnesium alloys and manufacturing routes. One example of this is the application of 319 Al alloy for production of 3.6L V6 gasoline engine blocks. Aluminum is sand cast around Fe-liner cylinder inserts, prior to undergoing the T7 heat treatment process. One of the critical factors determining the quality of the final product is the type, level, and profile of residual stresses along the Fe liners (or extent of liner distortion) that are always present in a cast component. In this study, neutron diffraction was used to characterize residual stresses along the Al and the Fe liners in the web region of the cast engine block. The strains were measured both in Al and Fe in hoop, radial, and axial orientations. The stresses were subsequently determined using generalized Hooke's law.

In recent years, light weight components have been an area of significant importance in automotive design. This has led to the replacement of steel and cast iron with aluminum alloys for many automotive components. For instance, Al-Si alloys have successfully replaced nodular and gray cast iron in the production of large automotive components such as engine blocks. However, excessive residual strain along the cylinder bores of these engine blocks may result in cylinder distortion during engine operation. Therefore, in this study, neutron diffraction was used to evaluate residual strain along the aluminum cylinder bridge and the gray cast iron liners of distorted and undistorted engine blocks. The strains were measured in the hoop, radial, and axial orientations. The results suggest that the residual strain along the aluminum cylinder bridge of the distorted engine block was tensile for all three measured components.

Presented in this paper is a framework for the implementation of a robotic percussive riveting system, a new robot application for aircraft assembly. It is shown here that a successful robot application to the automation of a process requires in-depth research of the process and the interaction with the robot. For this purpose, a process planning-driven approach is proposed to guide a robot application research. A typical process planning will involve a list of key considerations including: process sequence, process parameters, process tooling, and process control. Through this list, a number of key research issues are identified for robotic percussive riveting, such as rivet pattern planning, riveting time determination, riveting tooling design and rivet insertion control. The detailed research on these issues has effectively created know-how for the successful implementation of our robotic percussive riveting system.