Jonathan B. Ransom

Global/local stress analysis of composite panels☆

Abstract A method for performing a global/local stress analysis is described and its capabilities are demonstrated. The method employs spline interpolation functions which satisfy the linear plate bending equation to determine displacements and rotations from a global model which are used as “boundary conditions” for the local model. Then, the local model is analyzed independently of the global model of the structure. This approach can be used to determine local, detailed stress states for specific structural regions using independent, refined local models which exploit information from less-refined global models. The method presented is not restricted to having a priori knowledge of the location of the regions requiring local detailed stress analysis. This approach also reduces the computational effort necessary to obtain the detailed stress state. Criteria for applying the method are developed. The effectiveness of the method is demonstrated using a classical stress concentration problem and a graphite-epoxy blade-stiffened panel with a discontinuous stiffener.

A new interface element for connecting independently modeled substructures

A new interface element based on the hybrid variational formulation is presented and demonstrated. The element provides a means of connecting independently modeled substructures whose nodes along the common boundary need not be coincident. The interface element extends previous work to include connecting an arbitrary number of substructures, the use of closed and generally curved interfaces, and the use of multiple, possibly nested, interfaces. Several applications of the element are presented and aspects of the implementation are discussed.

Structural dynamic analysis on a parallel computer: The finite element machine

Abstract The development of general-purpose finite element computer software systems has provided the capability to analyze a wide range of linear and non-linear structural problems. However, these software systems are severely limited for non-linear response calculations because of the available speed on current sequential computers. Recent and projected advances in parallel multiple instruction multiple data (MIMD) computers provide an opportunity for significant gains in computing speed and for broadening the range of structural problems which may be solved. The key to these gains is the effective selection and implementation of algorithms which exploit parallel computing. This paper documents experiences solving transient response calculations on an experimental MIMD computer, termed the Finite Element Machine. The paper describes the algorithm used, its implementation for parallel computations, and results for representative one- and two-dimensional dynamic response test problems. The results show computation speedups of up to 7.83 for eight processors, and indicate that significant speedups of solution time are possible for non-linear dynamic response calculations through the use of many processors and appropriate parallel integration algorithms. The results are extremely encouraging and suggest that significant speedups in structural computations can be achieved through advances in parallel computers.

Global/local methods research using a common structural analysis framework

Methodologies for global/local stress analysis are described including both two- and three-dimensional analysis methods. These methods are being developed within a common structural analysis framework. Representative structural analysis problems are presented to demonstrate the global/local methodologies being developed.

INTERFACE TECHNOLOGY FOR GEOMETRICALLY NONLINEAR ANALYSIS OF MULTIPLE CONNECTED SUBDOMAINS

Interface technology for geometrically nonlinear analysis is presented and demonstrated. This technology is based on an interface element which makes use of a hybrid variational formulation to provide for compatibility between independently modeled connected subdomains. The interface element developed herein extends previous work to include geometric nonlinearity and to use standard linear and nonlinear solution procedures. Several benchmark nonlinear applications of the interface technology are presented and aspects of the implementation are discussed.

AN OVERVIEW OF INNOVATIVE STRATEGIES FOR FRACTURE MECHANICS AT NASA LANGLEY RESEARCH CENTER

Engineering fracture mechanics has played a vital role in the development and certification of virtually every aerospace vehicle that has been developed since the mid-20th century. NASA Langley Research Center s Durability, Damage Tolerance and Reliability Branch has contributed to the development and implementation of many fracture mechanics methods aimed at predicting and characterizing damage in both metallic and composite materials. This paper presents a selection of computational, analytical and experimental strategies that have been developed by the branch for assessing damage growth under monotonic and cyclic loading and for characterizing the damage tolerance of aerospace structures

Lessons Learned from Recent Failure and Incident Investigations of Composite Structures

During the past few decades, NASA Langley Research Center (LaRC) has supported several large-scale failure and incident investigations and numerous requests for engineering consultations. Although various extenuating circumstances contributed to each of these incidents, in all cases, the failure resulted from accumulation and/or propagation of damage that reduced the load carrying capability of the structure to a level below that which was needed to sustain structural loads. A brief overview of various failure and incident investigations supported by LaRC, including some of the computational and experimental methodologies that have been applied, is presented. An important outcome of many of these failure and incident investigations is the development of an improved understanding of not only the state-of-the-art in experimental and analytical methods but also the state-of-the-art in the design and manufacturing processes that may contribute to such failures. In order to provide insight into such large-scale investigations, a series of lessons learned were captured. Awareness of these lessons learned is highly beneficial to engineers involved in similar investigations. Therefore, it is prudent that the lessons learned are disseminated such that they can be built upon in other investigations and in ensuing research and development activities.

Probabilistic Analysis and Design of a Raked Wing Tip for a Commercial Transport

An approach for conducting reliability-based design and optimization (RBDO) of a Boeing 767 raked wing tip (RWT) is presented. The goal is to evaluate the benefits of RBDO for design of an aircraft substructure. A finite-element (FE) model that includes eight critical static load cases is used to evaluate the response of the wing tip. Thirteen design variables that describe the thickness of the composite skins and stiffeners are selected to minimize the weight of the wing tip. A strain-based margin of safety is used to evaluate the performance of the structure. The randomness in the load scale factor and in the strain limits is considered. Of the 13 variables, the wing-tip design was controlled primarily by the thickness of the thickest plies in the upper skins. The report includes an analysis of the optimization results and recommendations for future reliability-based studies.

An Overview of Durability and Damage Tolerance Methodology at NASA Langley Research Center

The NASA Langley Research Center’s Research Directorate provides many of the research and technology development capabilities required by the present and future needs of NASA across three encompassing technology areas, namely, aerodynamics, aerothermodynamics and acoustics (AAA); structures and materials (SM); and Airborne Systems (AirSc). Researchers contribute to nine primary areas of expertise which include structures, hypersonics, materials, flight dynamics and control, measurement sciences, crew systems and aviation operations, aerodynamics, safety critical avionics systems, and acoustics. These areas of expertise cover virtually all of the important disciplines related to flight, including the agency’s main thrusts within structures and materials. Researchers in the structures and materials technology area are constantly working to develop advanced materials to enable efficient, high-performance aerospace concepts; efficient, physics-based analytical and computational methods for multidisciplinary design and analysis; and methods to quantify the behavior, durability, damage tolerance, and overall performance of advanced materials and structures.As part of the structures and materials technology area, the Durability, Damage Tolerance and Reliability Branch (DDTRB) conducts research and technology development of efficient, physics-based analytical and computational methods to enable multidisciplinary design and analysis of advanced materials and structures for aerospace applications, including evaluation of concepts, quantification of behavior, durability, and damage tolerance, and validation of performance.DDTRB has contributed to the development and implementation of many fracture mechanics methods aimed at predicting and characterizing damage in both metallic and composite materials. Engineering fracture mechanics plays a vital role in the development and certification of virtually every aerospace vehicle that has been developed since the mid-twentieth century. This chapter presents a selection of computational, analytical, and experimental strategies and methodologies that have been developed by the branch for simulating and assessing damage growth under monotonic and cyclic loading and for characterizing the damage tolerance of aerospace structures. It includes continuum-based mechanics as well as a new paradigm focused on simulating and characterizing fundamental damage processes, called damage science.