The broad scope of the research described herein is the integration of several components of engineering software using a relational database. More specifically, a conceptual finite element material preprocessing system for fiber-reinforced composite materials was studied. In this computer-aided analysis (CAA) system, a materials database is integrated with several software components, including commercially available finite element analysis (FEA) programs and preprocessors, and tools for the design of laminated composite materials. The focus of the system is on the integration of two- and three-dimensional composite materials data into several finite element analysis programs. Particular attention is given to analysis and design of components and structures using thick composite materials. Many engineering applications exist for thick composite structures; however, they have received less critical attention than the thin composite structures often used in aerospace applications. The primary objective of the composites analysis system is to enhance data transfer between and interaction among several engineering software programs with a minimum of user interaction. This paper describes a specific implementation of a computer-aided analysis system that achieves this objective, detailing the need for the system and describing each of its components, including a composite materials database. The capabilities of the integrated system are discussed, including tasks such as composite laminate design, data entry, report generation, and interface file generation, performed in support of the finite element analysis capability. A major focus of the paper is on the twofold role of the materials database in the analysis system, as both a passive data repository and as a dynamic data transfer mechanism. The use of interface programs and direct integration techniques are discussed in the context of passing materials data between the user and the database, and between the database and the various system components or application programs.

The Environment For Application Software Integration and Execution (EASIE) is a methodology and a set of software utility programs developed at the NASA Langley Research Center for coordinating the use of engineering design and analysis computer programs. Under user direction, EASIE controls the execution of independently developed programs and manages the flow of data to and from a common relational data base in order to accomplish design or analysis objectives. The process is highly automated. For example, a utility program generates a DATA DICTIONARY, describing the contents of the data base and the various subsets of data used by the application programs. Other utilities automatically generate FORTRAN or C subroutines to link the application programs with the database or to pre- and post-process the data. EASIE is also “user friendly,” providing “windows” into the data base to view subsets of the data and the means to modify the data at any time A key feature is the degree of independence it provides to the programmer and user from the details of the operating system and Data Base Management System. EASIE has been used successfully in the integration of several design systems at Langley and within the aerospace industry. This paper discusses the application of EASIE to these specific systems, emphasizing the advantages it has provided to both programmers and users. Significant improvements made as a result of these experiences will also be discussed.

Standards verification in a CALS environment can be a complex and demanding process requiring not only a complete understanding of the standard but also the planned application and software implementation. An area of particular concern is the adequacy of vector or geometry based standards such as IGES to represent engineering and manufacturing applications. In such cases the visual similarity of geometry can be an inadequate test of the validity of a data exchange. Analytically oriented use of the geometry representation of some design and manufacturing applications may require very precise exchange of geometric entities. This paper will focus on testing strategies to provide comprehensive evaluations of vector based geometry standards such as IGES for engineering analysis, design and manufacturing use. The tests will show effective ways to measure whether vendor translators adequately capture key behavior needed in such applications. Results will be illustrated through tests at the Georgia Tech CALS Research Center which includes several different workstations and associated CAD software systems. CALS Class II test suites taken from representative aerospace applications are used to illustrate these concepts. The results show the importance of such testing in the verification of future CALS standards built around the PDES/STEP efforts. Finally the paper will outline the role and importance of an analytic testing facility in a comprehensive academic research program on information technology for engineering and how it influences current and future engineering education.

The five-axis constrained and optimal orientation planning is formulated as a design optimization problem that incorporates the process machine’s kinematic constraints with the workpiece and tool geometry, to obtain a constrained setup orientation which exploits the maximum capabilities of existing machines. This work will introduce this problem, and will obtain the setup orientation for two different types of rotation structures, i.e., tool rotation and table rotation in O(N) time. Further, the obtained constrained setup orientation, will be augmented to incorporate the workpiece surface magnitude, along with different machine rotation structures, to obtain an optimal setup orientation for different machine rotation structures. The drilling process is also introduced and formulated as additional constraints to the optimization problem. The primary application of the introduced algorithms, is the machining process, where, they can efficiently reduce the number of tool motions and surface finishing processes. However, the solution is very suitable for many manufacturing applications, such as inspection, assembly, robotics, painting, welding, aerospace, electronic surface mount technology, and etc.

Fatigue data obtained under biaxial loading conditions for adhesively bonded joints are used to plot S-N type diagrams to assess the effects of biaxiality in loading. Independently Loaded Mixed-Mode Specimens (ILM MS) are used for data collection purposes. These specimens are basically two (steel) beams bonded to be fatigue loaded under cantilever (opening) mode while a simultaneous but physically separate in-plane (static) shear load is also induced with the aid of a small hydraulic piston embedded in the specimen. Application of such static shear loads results in different S-N behavior for the bonded joint. The model adhesives used are Metlbond 1113-2 and Metlbond 1113 solid film thermosetting adhesives similar to those commonly used in aircraft and aerospace industries. The former is an elastomer-modified epoxy adhesive and the latter is identical except that it containes a synthetic earner cloth. Thus, the effects of carrier cloth in adhesive’s S-N behavior is also assessed. Analytically, the classical linear log-log representation of the adhesive S-N data is explored and modifications necessary to reflect the effects of biaxiality in loading and also the presence of a carrier cloth are assessed. The fatigue failure results are also compared with results obtained under monotonic biaxial loading conditions.

A computational methodology has been developed to predict the fatigue life of typical aerospace components, here the specific example is a circumferentially reinforced SiC/Ti-15-3 compressor ring designed for applications at 800° F. The analysis encompasses both a static burst pressure prediction and a life assessment of the cladded ring. A three dimensional stress analysis was performed using MARC, a nonlinear finite element code, wherein both the matrix cladding and the composite core were assumed to behave elastic-plastic. The composite core behaviour was represented using Hill’s anisotropic continuum based plasticity model with bilinear hardening. Similarity, the matrix cladding was represented by an isotropic perfectly plastic model. The load-displacement (i.e., internal pressure versus radial deflection) response of the ring was used to determine the static burst pressure. The life assessment was conducted using the stress analysis results, in conjunction with a recently developed multiaxial, isothermal, continuum damage mechanics model for the fatigue of unidirectional metal matrix composites. This model is phenomenological, stress based, and assumes a single scalar internal damage variable, the evolution of which is anisotropic. The accumulation of damage is included in the stress analysis by employing the concept of effective stress. In the current application, however, the damage model is computationally-decoupled from the finite element solution. The specific methodology for this computationally-decoupled fatigue damage simulation is outlined and results are given in terms of the evolution of damage and design life curves.

The boring bar is used to provide smooth, accurate cuts in materials. However, when the length to diameter (L/D) ratio of the boring bar becomes large, low-frequency vibration, or chatter, results. Initial attempts to control this unwanted vibration with an active absorber have been successful, but in some configurations problems remain. In this paper, algorithms for flexible structure identification widely used in the aerospace industry are applied to a number of boring bar setups to identify the vibration characteristics of each system. Emphasis is placed on one class of methods which includes the Eigensystem Realization Algorithm (ERA), developed for identification of flexible space structures. The resulting identified characteristics are compared and contrasted. Results are also compared to finite element analysis predictions. From the current identification results, implications for chatter control are discussed, including the possibility of nonlinear modal interactions.

The study of the non-stationary response of systems has many applications in problems related to transition through resonance in rotating machinery, aerospace structures and other physical systems. In this paper, we present methods to analytically predict the response of some weakly nonlinear systems to slowly varying parameter changes. We consider systems which can be averaged and represented as two first order equations. The evolution of the solutions of such systems through critical (jump or bifurcation) points is studied using the method of matched asymptotic expansions. As an example, the method is used to predict the response of the forced Duffing’s oscillator during passage through resonance. Starting with a general system of two, first-order equations, we set up a slowly varying equilibrium or ‘outer’ solution as an asymptotic expansion about the stationary solution. This solution is seen to be invalid in a small neighborhood of the critical points — the ‘inner’ region. In this inner layer, the system of equations is transformed into the Jordan canonical form, which is easier to study. Using approximations from the center manifold theory, the problem is reduced to one first-order equation. By making appropriate scale changes, an ‘inner’ solution is developed. This solution is asymptotically matched with the outer expansion to yield a unified solution valid for all time.

The study of the transverse vibration of thin rectangular plates has been mainly confined to plates of uniform thickness. There are few publications available on the vibration of plates with nonuniform thickness. These plates have application in various fields such as civil engineering and aerospace structures and are often found in high frequency acoustic transducers. Furthermore, it is sometimes possible to achieve minimum weight design of plates by having suitable variations in thickness. For the special case of a plate with two opposite edges simply supported and thickness discontinuities perpendicular to the simply supported edges, an analytical solution is possible using a dynamic flexibility method. Several examples are discussed.

We describe a design process recording method and a prototype implementation. They are being developed from data on several design projects, including an in-depth study of a 6-month long design effort, itself part of a multi-year aerospace research and design project. The work is also influenced by the larger context of other design research projects at Stanford. The recording method focuses on information generated in early stages of design that is at the same time easiest to capture and most useful to designers and engineers downstream. It does this by being based primarily on a design process model intended to reflect a designer’s point of view, and by taking advantage of practices that designers currently find useful. The method builds on the concept of an electronic notebook that has been described previously (Lakin et al., 1989). The record consists of connected pieces of information about the various concepts, notes, and documents that are central to an evolving design. We call the framework for the record a hypergraph: ‘graph’ because of its node-arc structure, and ‘hyper’ because it spans several types of information that are created during design work. To effectively convey the record’s contents to a downstream user, we propose a design story-teller style: the system’s response to a query takes the form of a storyboard of notes about related design episodes.

The experimental stress analysis technique using the thermoelastic effect is quite recent. Besides being a non-contact method, the technique is able to produce a full field analysis. These attributes, associated with the possibility of application to structures or components in their operating environment, make the technique appealing for use in an industrial context. The thermoelastic effect is the change in temperature arising from the change in the stress state of a solid. The stress analysis technique using this effect measures the infra-red radiation emitted from a modification in its stress state. The applicability of the relationship between change in temperature and change in the stress state, as described in the theory of thermoelasticity, requires the existence of adiabatic conditions. Thus, the body to be studied must be subjected to a cyclic loading of a frequency sufficient to ensure those conditions. Adhesives are being used increasingly in more demanding applications not only in non-load carrying situations but also in structural applications as an alternative to other joining techniques. The use of adhesives in structural applications requires understanding the global behavior of structures as well as the behavior of the adhesive connections. Stress analysis of those connections is an important step towards that goal. Lap-shear joints are a type of adhesive connections widely used in industrial applications, namely, in the aerospace and automotive industries. In this study, stress analyses of these connections were performed. The experimental stress analysis technique using the thermoelastic effect was used to determine the stress state at a surface of adhesive lap-shear joints. The results were compared with finite element analyses of the same joints.

One possible approach to life extension of aerospace components is to take those parts or subsystems that have run the limited initial life estimate and been removed from service, and to operate them in simulated service for periods of time beyond the initial life estimate. It is often the case that such testing must be suspended before the part reaches the point of actual failure. A need therefore exists to use such suspended test data to infer a life limit. The standard deviation of the estimated life can generally be reliably quantified by applying results from laboratory material tests and information on the variability of the unit’s dimensions. The derived life estimate must therefore be consistent with the known standard deviation. The problem is structured as a variational one, that is, a problem of finding the values of a set of variables — the hypothetical duration of the individual suspended tests if they had been continued to failure — subject to the constraints that the period of continuation must be equal to or greater that zero, and that the standard deviation of the average value of the life of the sample set be equal to the known, predetermined value. The problem is made determinate by applying the conservative requirement that calculated average life of the sample set be the lowest possible value. Although the problem is nonlinear and not amenable to traditional linear programming solution, a very simple pair of algorithms have been identified which permit exact solution for all ranges of objective standard deviation. Solutions to typical problems are given to illustrate the utility of the procedure.

This paper introduces a novel approach to three dimensional routing optimization. Examples of routing tasks for engineering applications include routing of pipes, wires and air ducts. Traditionally, routing algorithms perform Manhattan, or orthogonal, routing. Non-orthogonal routing can be less costly than Manhattan routing and for applications such as automotive or aerospace design, Manhattan routing is impractical due to spatial limitations. The research presented in this paper uses simulated annealing as the basis of a non-orthogonal routing optimization algorithm that avoids the drawbacks associated with Manhattan routing. Several examples comparing the two approaches are given.

A new technology, called Stress Coupling Activated Damping (SCAD © ), was applied successfully to a lathe boring bar. It reduced high frequency vibrations by up to 20 db. It can be applied to a wide range of structural designs. The geometries of the damped structures are not limited to thin plates but can be applied to tubes, I-beams, and complex structures. This allows SCAD © technology to be applied to several industry design problems, including the metrology, medical, aerospace, automotive and machine tool industries. SCAD © will also allow boring bars to: 1) be optimized for stiffness, frequency and loss factor, 2) be ‘tuned’ to a specific resonant frequency, 3) have improved damping regardless of boring bar diameter, 4) lengthen the usable tool length without a significant increase in cost, and 5) decrease cutting surface vibration induced pattern.

High cycle fatigue loading of gear webs due to in-plane stresses, caused by forced excitation resulting from centrifugal loading and dynamic tooth loads, has been known to cause radial fatigue cracks. This is especially prevalent in high-speed gears used in aerospace applications, with small web thickness, for weight reduction. Radial cracks have also been observed to originate at the outer edge of lightening holes machined in gear webs for weight reduction. This paper presents an analytical treatment of the in-plane vibration of high-speed gear webs resulting from rotational effects and periodic excitation from dynamic tooth loading. Dynamic tooth loads result from the combined effect of inertia forces of gear wheels which are significant at high speeds, the periodic variation of gear mesh stiffness, and involute tooth profile errors. The gear web is modeled as a thin rotating disc and the governing differential equations of motion and the associated boundary conditions are derived from first principles. A comprehensive tooth stiffness model for spur gears is used that accounts for periodic variation of mesh stiffness. The dynamic tooth loads are obtained by solving the pertinent equations of motion, using a collocation method, that yields a closed-form expression for the periodic excitation, that is used as an input for the in-plane vibration problem. The in-plane vibration equations are solved by an approximate method of weighted residuals. It is found that the displacement fields and the resulting stresses can be significant under certain speeds and loading conditions. The in-plane stresses leading to high cycle fatigue loading, and frequency components of the resulting response are discussed in detail.

This paper presents an improved analysis method for the interpretation of the vibration data measured at turbomachinery blade tips using optical laser probes. A multi-degree-of-freedom numerical simulator, which includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms and the characteristics of the optical probe, has been developed to assess the reliability of the various data processing techniques to identify the natural frequencies and mode shapes of bladed-disk assemblies. It has been demonstrated that the Zablotsky-Korostelev single parameter technique, which is a de-facto standard in the aerospace industries, has inherent limitations associated with it. An improved and more rigorous method is presented for deriving the blade arrival times and a non-linear solution technique is suggested for their numerical determination. Finally, the effect of blade mistuning on the accuracy of the proposed method is also investigated.

The prediction and analysis of response of laminated composite shell structures under nonstationary random excitation is of considerable interest to design engineers in aerospace and automobile engineering fields. However, it seems that there is no known comprehensive published work on such an analysis that employs the versatile finite element method. Thus, the main focus of the investigation reported in this paper is the application of the hybrid strain-based laminated composite flat triangular shell finite element, that has been developed by the authors, for the analysis of laminated composite shell structures under a relatively wide class of nonstationary random excitations. Representative results of a simply-supported laminated composite cylindrical panel subjected to a point nonstationary random excitation are included.

Dimensional inspection of 3D objects with complex sculptured surfaces is an important issue, due to the increase in precision manufacturing of dies, patterns, moulds, turbine blades, forged parts, and aerospace structural components. In order to determine the error on a machined surface, the measured points must be located in the design coordinate system of the part. This is called localization. This paper presents an approach which formulates the problem as least squares minimization of distances, with the solution being achieved through self learning neural network. The shortest distance between the measured points and their counterparts on the parametric design surface are determined by solving simultaneous non-linear equations. The neural network is then used to learn the homogeneous transformation matrix. Results obtained from computer simulations performed for both scattered and dense data are presented. The results indicate that the proposed method using neural network is both computationally efficient and robust.

New aerospace designs will incorporate new concepts as a result of advances made in the scientific and engineering technologies. These new concepts will afford the aircraft designer with an interesting and somewhat envious dilemma. The aircraft designer will have unprecedented flexibility in design concepts. However, this new flexibility will often be paralleled in ever increasing design complexity. Aircraft such as the High Speed Civil Transport (HSCT) will provide a design environment which will require the efficient use of new technologies in an arena which has historically proven to have stringent performance and cost goals which must be met in order to result in a successful design. The complexity of the HSCT design will dictate a close multidisciplinary effort requiring large amounts of data exchange. Moreover, with the enormous development costs associated with such a design, corporate teaming is essential. It is critical to the success of the HSCT and future aircraft design that a new approach be taken toward the management and exchange of information. A top-down data management design structure should be developed and implemented in the early stages in order to optimize the design process. A small scale multidisciplinary relational database management design has been developed for the HSCT in order to gain a better understanding of how efficient data management can optimize the aircraft design process.

A method for the sensitivity analysis of the dynamic transient response of flexible multi-body systems is presented. The main objectives in developing the method are: 1) to reduce cost and achieve accuracy of the sensitivity analysis, 2) to develop a performent tool for the sensitivity analysis and the optimization of flexible multi-body systems. Practical applications are located in the automotive industry, with the optimization of the driving behavior of vehicles and in the aerospace industry. The method consists in solving simultaneously the dynamic and the sensitivity problem. Two simple examples are presented to demonstrate the method, one for a dynamic response problem, and the second one for a kinematic problem.