A review of some approximate analytical models for damaged, fiber reinforced composite materials is presented. Using the classical shear lag stress displacement assumption, solutions are presented for a unidirectional laminate containing a notch, a rectangular cut-out, and a circular hole. The models account for longitudinal matrix yielding and splitting as well as transverse matrix yielding and fiber breakage. The constraining influence of a cover sheet on the unidirectional laminate is also...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FIBER COMPOSITES, FRACTURE MECHANICS,...

The problem of calculating expected component life under fatigue loading conditions is complicated by the fact that component loading histories contain, in many cases, cyclic loads of widely varying amplitudes. In such a case a cumulative damage model is required, in addition to a fatigue damage criterion, or life relationship, in order to compute the expected fatigue life. The traditional cumulative damage model used in design is the linear damage rule. This model, while being simple to use,...

Topics: NASA Technical Reports Server (NTRS), COMPONENT RELIABILITY, FATIGUE (MATERIALS), LIFE...

Liquid rocket booster integration study is presented. Volume 4 contains materials presented at the MSFC/JSC/KSC Integrated Reviews and Working Group Sessions, and the Progress Reviews presented to the KSC Study Manager. The following subject areas are covered: initial impact assessment; conflicts with the on-going STS mission; access to the LRB at the PAD; the activation schedule; transition requirements; cost methodology; cost modelling approach; and initial life cycle cost.

Topics: NASA Technical Reports Server (NTRS), BOOSTER ROCKET ENGINES, COSTS, MATHEMATICAL MODELS, RESEARCH...

Defects in fiber composite components produce changes with respect to the vibrational characteristics of the material. These changes can be recognized in the form of a frequency shift or an alteration of the damping process. The present investigation is concerned with questions regarding the possibility of a utilization of the changes in suitable defect-detecting inspection procedures. A description is given of a method for measuring the damping characteristics of a specimen. This method...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FIBER COMPOSITES, FREQUENCY SHIFT,...

As a consequence of preparations concerning the International Space Welding Experiment (ISWE), studies were performed to better understand the effect of molten metal contact and electron beam impingement with various fabrics for space suit applications. The question arose as to what would occur if the electron beam from the Ukrainian Universal Hand Tool (UHT) designed for welding in space were to impinge upon a piece of Nextel AF-62 ceramic cloth designed to withstand temperatures up to 1427 C....

Topics: NASA Technical Reports Server (NTRS), OUTGASSING, ELECTRON BEAM WELDING, SPACE SUITS, COMBUSTION...

This report discusses a methodology that can be used to assess the effect of foreign body impacts on composite structural integrity. The described effort focuses on modeling the effect of a central impact on a 5 3/4 inch filament wound test article. The discussion will commence with details of the material modeling that was used to establish the input properties for the analytical model. This discussion is followed by an overview of the impact assessment methodology. The progress on this effort...

Topics: NASA Technical Reports Server (NTRS), COMPOSITE STRUCTURES, DAMAGE ASSESSMENT, IMPACT DAMAGE,...

NASAâ€™s Orbital Debris Engineering Model was designed to calculate orbital debris fluxes on spacecraft in order to assess collision risk. The newest of these models, ORDEM 3.0, has a number of features not present in previous models. One of the most important is that the populations and fluxes are now broken out into material density groups. Previous models concentrated on debris size alone, but a particleâ€™s mass and density also determine the amount of damage it can cause. ORDEM 3.0...

Topics: NASA Technical Reports Server (NTRS), SPACE DEBRIS, MATHEMATICAL MODELS, RISK, MATERIALS, DAMAGE...

A procedure is proposed for the assessment of the damage tolerance and collapse of stiffened composite panels using a single-stringer compression specimen. The dimensions of the specimen are determined such that the specimen s nonlinear response and collapse are representative of an equivalent multi-stringer panel in compression. Experimental tests are conducted on specimens with and without an embedded delamination. A shell-based finite element model with intralaminar and interlaminar damage...

Topics: NASA Technical Reports Server (NTRS), BUCKLING, COMPOSITE STRUCTURES, DAMAGE ASSESSMENT, CRACK...

Model-based prognostics approaches capture system knowledge in the form of physics-based models of components, and how they fail. These methods consist of a damage estimation phase, in which the health state of a component is estimated, and a prediction phase, in which the health state is projected forward in time to determine end of life. However, the damage estimation problem is often multi-dimensional and computationally intensive. We propose a model decomposition approach adapted from the...

Topics: NASA Technical Reports Server (NTRS), CENTRIFUGAL PUMPS, DECOMPOSITION, STRUCTURAL ENGINEERING,...

A simple model to study low velocity transverse impact of thin plates made of fiber-reinforced composite material, in particular T300/5208 graphite-epoxy was discussed. This model predicts the coefficient of restitution, which is a measure of the energy absorbed by the target during an impact event. The model is constructed on the assumption that the plate is inextensible in the fiber direction and that the material is incompressible in the z-direction. Such a plate essentially deforms by...

Topics: NASA Technical Reports Server (NTRS), DEFORMATION, ENERGY ABSORPTION, FIBER COMPOSITES,...

Spacecraft are susceptible to structural damage over their operating life from impact, environmental loads, and fatigue. Structural damage that is not detected and not corrected may potentially cause more damage and eventually catastrophic structural failure. NASA's current fleet of reusable spacecraft, namely the Space Shuttle, has been flown on several missions. In addition, configurations of future NASA space structures, e.g. Space Station Freedom, are larger and more complex than current...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FLEXIBLE SPACECRAFT, LARGE SPACE...

The need for monitoring the dynamic characteristics of large structural systems for purposes of assessing the potential degradation of structural properties was established. A theory for assessing the occurrence, location, and extent of potential damage was developed utilizing on-orbit response measurements. Feasibility of the method is demonstrated using a simple structural system as an example.

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, DEGRADATION, DYNAMIC STRUCTURAL ANALYSIS,...

The development of validated multidisciplinary Integrated Vehicle Health Management (IVHM) tools, technologies, and techniques to enable detection, diagnosis, prognosis, and mitigation in the presence of adverse conditions during flight will provide effective solutions to deal with safety related challenges facing next generation aircraft. The adverse conditions include loss of control caused by environmental factors, actuator and sensor faults or failures, and damage conditions. A major...

Topics: NASA Technical Reports Server (NTRS), CHARACTERIZATION, DAMAGE ASSESSMENT, STRUCTURAL HEALTH...

A mechanical test technique was developed to assist in quantifying the accumulation of damage in composite materials during thermomechanical fatigue (TMF) cycling. This was accomplished by incorporating definitive elastic mechanical property measurements into an ongoing load-controlled TMF test without disturbing the test specimen or significantly altering the test conditions. The technique allows two fundamental composite properties consisting of the isothermal elastic static moduli and the...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FATIGUE TESTS, METAL MATRIX COMPOSITES,...

A probabilistic model utilizing random material characteristics to predict damage evolution in textile laminates is presented. Model is based on a division of each ply into two sublaminas consisting of cells. The probability of cell failure is calculated using stochastic function theory and maximal strain failure criterion. Three modes of failure, i.e. fiber breakage, matrix failure in transverse direction, as well as matrix or interface shear cracking, are taken into account. Computed failure...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, LAMINATES, MATHEMATICAL MODELS, STOCHASTIC...

The concept of Life Extending Control (LEC) is introduced. Possible extensions to the cyclic damage prediction approach are presented based on the identification of a model from elementary forms. Several candidate elementary forms are presented. These extensions will result in a continuous or differential form of the damage prediction model. Two possible approaches to the LEC based on the existing cyclic damage prediction method, the measured variables LEC and the estimated variables LEC, are...

Topics: NASA Technical Reports Server (NTRS), COMPONENT RELIABILITY, DAMAGE ASSESSMENT, HYDRAULIC...

Solutions are developed for the two dimensional region containing unidirectional fibers with initial damage in the form of a notch, a rectangular cut out, and a circular hole. An ultimate stress failure criterion is used for both the fibers and the matrix, simple tension for the fibers, and shear failure for the matrix. Models which account for longitudinal matrix yielding and splitting as well as transverse matrix yielding and fiber breakage as a function of initial damage, material...

Topics: NASA Technical Reports Server (NTRS), CRACK PROPAGATION, FIBER COMPOSITES, FRACTURE MECHANICS,...

This rapid response computer program predicts Orbiter Wing Leading Edge (WLE) damage caused by ice or foam impact during a Space Shuttle launch (Program "IMPACT2"). The program was developed after the Columbia accident in order to assess quickly WLE damage due to ice, foam, or metal impact (if any) during a Shuttle launch. IMPACT2 simulates an impact event in a few minutes for foam impactors, and in seconds for ice and metal impactors. The damage criterion is derived from results...

Topics: NASA Technical Reports Server (NTRS), LEADING EDGES, WINGS, DAMAGE, MATHEMATICAL MODELS, STRUCTURAL...

An overview and data analyses pertaining to cavitation erosion size scale effects are presented. The exponents n in the power law relationship are found to vary from 1.7 to 4.9 for venturi and rotating disk devices supporting the values reported in the literature. Suggestions for future studies were made to arrive at further true scale effects.

Topics: NASA Technical Reports Server (NTRS), CAVITATION CORROSION, DESIGN ANALYSIS, SCALING LAWS, TURBINE...

This paper describes how damage propagation can be modeled within the modules of aircraft gas turbine engines. To that end, response surfaces of all sensors are generated via a thermo-dynamical simulation model for the engine as a function of variations of flow and efficiency of the modules of interest. An exponential rate of change for flow and efficiency loss was imposed for each data set, starting at a randomly chosen initial deterioration set point. The rate of change of the flow and...

Topics: NASA Technical Reports Server (NTRS), DAMAGE, SIMULATION, MATHEMATICAL MODELS, AIRCRAFT ENGINES,...

A high temperature, low cycle fatigue life prediction method was developed. This method, Cyclic Damage Accumulation (CDA), was developed for use in predicting the crack initiation lifetime of gas turbine engine materials, where initiation was defined as a 0.030 inch surface length crack. A principal engineering feature of the CDA method is the minimum data base required for implementation. Model constants can be evaluated through a few simple specimen tests such as monotonic loading and rapic...

Topics: NASA Technical Reports Server (NTRS), CRACK INITIATION, DAMAGE ASSESSMENT, HEAT RESISTANT ALLOYS,...

On-orbit testing of a large space structure will be required to complete the certification of any mathematical model for the structure dynamic response. The process of establishing a mathematical model that matches measured structure response is referred to as model correlation. Most model correlation approaches have an identification technique to determine structural characteristics from the measurements of the structure response. This problem is approached with one particular class of...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, DYNAMIC RESPONSE, LARGE SPACE STRUCTURES,...

The fracture behavior of a debonded zone of finite width with no longitudinal damage in the unidirectional ply is predicted and the solution is then extended to include longitudinal matrix yielding and splitting in the unidirectional ply at the crack tip. The shear-lag assumption is used to describe the shear transfer between fibers. The fracture behavior of the laminate is studied as a function of initial crack length, constraint ratio, and width of the debonded zone. Results indicate that...

Topics: NASA Technical Reports Server (NTRS), CRACK ARREST, DELAMINATING, FIBER COMPOSITES, FRACTURES...

Effective Total Fatigue Life and Crack Growth Scatter Models are proposed. The first of them is based on the power form of the Wohler curve, fatigue scatter dependence on mean life value, cycle stress ratio influence on fatigue scatter, and validated description of the mean stress influence on the mean fatigue life. The second uses in addition are fracture mechanics approach, assumption of initial damage existence, and Paris equation. Simple formulas are derived for configurations of models. A...

Topics: NASA Technical Reports Server (NTRS), CRACK PROPAGATION, DAMAGE ASSESSMENT, FATIGUE LIFE, FRACTURE...

Computational tools have been developed to estimate thermal and mechanical reentry loads experienced by the Space Shuttle Orbiter as the result of cavities in the Thermal Protection System (TPS). Such cavities can be caused by impact from ice or insulating foam debris shed from the External Tank (ET) on liftoff. The reentry loads depend on cavity geometry and certain Shuttle state variables, among other factors. Certain simplifying assumptions have been made in the tool development about the...

Topics: NASA Technical Reports Server (NTRS), THERMAL PROTECTION, DAMAGE ASSESSMENT, IMPACT, SPACE SHUTTLE...

This historical work couples model order reduction, damage detection, dynamic residual/mode shape expansion, and damage extent estimation to overcome the incomplete measurements problem by using an appropriate undamaged structural model. A contribution of this work is the development of a process to estimate the full dynamic residuals using the columns of a spring connectivity matrix obtained by disassembling the structural stiffness matrix. Another contribution is the extension of an...

Topics: NASA Technical Reports Server (NTRS), MATHEMATICAL MODELS, COUPLED MODES, MODAL RESPONSE,...

Independent of the modal identification techniques employed for damage detection, use of measured modal data limits the expectations for damage location. These limitations are examined using the distribution of modal strain energy and the sensitivity of the frequency and mode shapes to structural stiffness changes. For given measured modal information of specific accuracy, this examination reveals the following: (1) damage detection is feasible for members that contribute significantly to the...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, DETECTION, MATHEMATICAL MODELS, MODAL...

A constitutive theory for use in structural and durability analyses of high temperature isotropic alloys is presented. Constitutive equations based upon a potential function are determined from conditions of stability and physical considerations. The theory is self-consistent; terms are not added in an ad hoc manner. It extends a proven viscoplastic model by introducing the Kachanov-Rabotnov concept of net stress. Material degradation and inelastic deformation are unified; they evolve...

Topics: NASA Technical Reports Server (NTRS), CONSTITUTIVE EQUATIONS, DAMAGE ASSESSMENT, HEAT RESISTANT...

LS-DYNA simulations were conducted to study the influence of model complexity on the response of a typical Reinforced Carbon-Carbon (RCC) panel to a foam impact at a location approximately midway between the ribs. A structural model comprised of Panels 10, 11, and TSeal 11 was chosen as the baseline model for the study. A simulation was conducted with foam striking Panel 10 at Location 4 at an alpha angle of 10 degrees, with an impact velocity of 1000 ft/sec. A second simulation was conducted...

Topics: NASA Technical Reports Server (NTRS), FINITE ELEMENT METHOD, LEADING EDGES, PANELS, MATHEMATICAL...

Graphite/epoxy composites are extensively used in the aerospace and sporting goods industries due to their superior engineering properties compared to those of metals. However, graphite/epoxy is extremely susceptible to impact damage which can cause considerable and sometimes undetected reduction in strength. An inelastic impact model was developed to predict damage due to low-velocity impact. A transient dynamic finite element formulation was used in conjunction with the 3D Tsai-Wu failure...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FAILURE ANALYSIS, FILAMENT WINDING,...

An equivalent plate procedure is developed to provide a computationally efficient means of matching the stiffness and frequencies of flight vehicle wing structures for prescribed loading conditions. Several new approaches are proposed and studied to match the stiffness and first five natural frequencies of the two reference models with and without damage. One approach divides the candidate reference plate into multiple zones in which stiffness and mass can be varied using a variety of materials...

Topics: NASA Technical Reports Server (NTRS), FREQUENCY RESPONSE, WINGS, AIRCRAFT STRUCTURES, PLATES...

Progressive damage and fracture of composite structures subjected to monotonically increasing static, tension-tension cyclic, pressurization, and flexural cyclic loading are evaluated via computational simulation. Constituent material properties, stress and strain limits are scaled up to the structure level to evaluate the overall damage and fracture propagation for composites. Damage initiation, growth, accumulation, and propagation to fracture due to monotonically increasing static and cyclic...

Topics: NASA Technical Reports Server (NTRS), COMPOSITE STRUCTURES, FATIGUE (MATERIALS), COMPUTERIZED...

The results of an experimental/numerical campaign aimed to develop progressive damage analysis (PDA) tools for predicting the strength of a composite bonded joint under tensile loads are presented. The PDA is based on continuum damage mechanics (CDM) to account for intralaminar damage, and cohesive laws to account for interlaminar and adhesive damage. The adhesive response is characterized using standard fracture specimens and digital image correlation (DIC). The displacement fields measured by...

Topics: NASA Technical Reports Server (NTRS), BONDED JOINTS, DAMAGE ASSESSMENT, CONTINUUM MECHANICS,...

As gas turbine technology continues to advance, the need for advanced life prediction methods for hot section components is becoming more and more evident. The complex local strain and temperature histories at critical locations must be accurately interpreted to account for the effects of various damage mechanisms (such as fatigue, creep, and oxidation) and their possible interactions. As part of the overall NASA HOST effort, this program is designed to investigate these fundamental damage...

Topics: NASA Technical Reports Server (NTRS), AXIAL STRESS, CREEP PROPERTIES, FATIGUE LIFE, GAS TURBINE...

This document provides an overview of recent accomplishments and lessons learned in the development of general progressive damage analysis methods for predicting the residual strength and life of composite structures. These developments are described within their State-of-the-Art (SoA) context and the associated technology barriers. The emphasis of the authors is on developing these analysis tools for application at the structural level. Hence, modeling of damage progression is undertaken at...

Topics: NASA Technical Reports Server (NTRS), COMPOSITE STRUCTURES, AIRCRAFT STRUCTURES, DAMAGE ASSESSMENT,...

Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a...

Topics: NASA Technical Reports Server (NTRS), ALUMINUM ALLOYS, COPPER ALLOYS, CRACK PROPAGATION, CRACK...

The concept of life extending control is defined. A brief discussion of current fatigue life prediction methods is given and the need for an alternative life prediction model based on a continuous functional relationship is established. Two approaches to life extending control are considered: (1) the implicit approach which uses cyclic fatigue life prediction as a basis for control design; and (2) the continuous life prediction approach which requires a continuous damage law. Progress on an...

Topics: NASA Technical Reports Server (NTRS), FATIGUE LIFE, MATHEMATICAL MODELS, NONLINEAR PROGRAMMING,...

This paper describes a series of modal tests that were performed on a cantilevered truss structure. The goal of the tests was to assemble a large database of high quality modal test data for use in verification of proposed methods for on orbit model verification and damage detection in flexible truss structures. A description of the hardware is provided along with details of the experimental setup and procedures for 16 damage cases. Results from selected cases are presented and discussed....

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FLEXIBLE SPACECRAFT, GROUND TESTS, LARGE...

Constitutive and life prediction models are developed and verified for materials typically used in hot gas path components of reusable space propulsion systems over the range of relevant operating environments. The efforts were centered on the development of crack initiation life prediction methods, while the efforts of a counterpart group were centered on the development of cyclic crack propagation life prediction methods. The complexion of the active tasks are presented. A significant new...

Topics: NASA Technical Reports Server (NTRS), COMPUTER PROGRAMS, FATIGUE (MATERIALS), FRACTURE MECHANICS,...

The results of an experimental/numerical campaign aimed to develop progressive damage analysis (PDA) tools for predicting the strength of a composite bonded joint under tensile loads are presented. The PDA is based on continuum damage mechanics (CDM) to account for intralaminar damage, and cohesive laws to account for interlaminar and adhesive damage. The adhesive response is characterized using standard fracture specimens and digital image correlation (DIC). The displacement fields measured by...

Topics: NASA Technical Reports Server (NTRS), BONDED JOINTS, ADHESIVES, COHESION, CONTINUUM MECHANICS,...

The objective of this program is to establish a methodology to predict Thermal Barrier Coating (TBC) life on gas turbine engine components. The approach involves experimental life measurement coupled with analytical modeling of relevant degradation modes. The coating being studied is a flight qualified two layer system, designated PWA 264, consisting of a nominal ten mil layer of seven percent yttria partially stabilized zirconia plasma deposited over a nominal five mil layer of low pressure...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FAILURE ANALYSIS, MATHEMATICAL MODELS,...

In thin composite laminates, the first level of visible damage occurs in the back face and is called back face spalling. A plate-membrane coupling model, and a finite element model to analyze the large deformation behavior of eight-ply quasi-isotropic circular composite plates under impact type point loads are developed. The back face spalling phenomenon in thin composite plates is explained by using the plate-membrane coupling model and the finite element model in conjunction with the fracture...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FINITE ELEMENT METHOD, FRACTURE MECHANICS,...

The multiple mesh/single stage dynamics program is a gear tooth analysis program which determines detailed geometry, dynamic loads, stresses, and surface damage factors. The program can analyze a variety of both epicyclic and single mesh systems with spur or helical gear teeth including internal, external, and buttress tooth forms. The modifications refine the options for the flexible carrier and flexible ring gear rim and adds three options: a floating Sun gear option; a natural frequency...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, DYNAMIC LOADS, GEAR TEETH, MATHEMATICAL...

This report summarizes the development of two physics-based scaling laws for describing crater depths and diameters caused by normal incidence impacts into aluminum and TFE Teflon. The report then describes equations for perforations in aluminum and TFE Teflon for normal impacts. Lastly, this report also studies the effects of non-normal incidence on cratering and perforation.

Topics: NASA Technical Reports Server (NTRS), ALUMINUM, CRATERING, CRATERS, DAMAGE ASSESSMENT, DIMENSIONAL...

The excellent mechanical properties of carbon-nanotubes are driving research into the creation of new strong, tough nanocomposite systems. In this program, our initial work presented the first evidence of toughening mechanisms operating in carbon-nanotube- reinforced ceramic composites using a highly-ordered array of parallel multiwall carbon-nanotubes (CNTs) in an alumina matrix. Nanoindentation introduced controlled cracks and the damage was examined by SEM. These nanocomposites exhibit the...

Topics: NASA Technical Reports Server (NTRS), CERAMIC MATRIX COMPOSITES, CARBON NANOTUBES, DAMAGE...

Personnel in the Quality and Integrity Design Engineering Center (QIDEC) at the University of Utah are working under a two year grant from the FAA to better understand the role of fretting corrosion and fretting fatigue in aircraft rivet hole cracking. The current program follows a one year grant program which was completed in 1993. This paper provides a status report on the results of these grant programs. Recent effort has been focused on developing basic fretting fatigue models which...

Topics: NASA Technical Reports Server (NTRS), AIRCRAFT STRUCTURES, COEFFICIENT OF FRICTION, CRACK GEOMETRY,...

A unified constitutive model is searched for that is applicable for high temperature superalloys used in modern gas turbines. Two unified inelastic state variable constitutive models were evaluated for use with the damage parameter proposed by Kachanov. The first is a model (Bodner, Partom) in which hardening is modeled through the use of a single state variable that is similar to drag stress. The other (Ramaswamy) employs both a drag stress and back stress. The extension was successful for...

Topics: NASA Technical Reports Server (NTRS), CONSTITUTIVE EQUATIONS, DAMAGE ASSESSMENT, HEAT RESISTANT...

A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive...

Topics: NASA Technical Reports Server (NTRS), CRACK GEOMETRY, CRACK INITIATION, CRACK PROPAGATION, CRACKING...

The objective of the research reported herein is to develop a progressive damage methodology capable of predicting the residual strength of continuous fiber-reinforced, laminated, polymer matrix composites with through-penetration damage. The fracture behavior of center-notch tension panels with thin crack-like slits was studied. Since fibers are the major load-carrying constituent in polymer matrix composites, predicting the residual strength of a laminate requires a criterion for fiber...

Topics: NASA Technical Reports Server (NTRS), LAMINATES, DAMAGE, POLYMER MATRIX COMPOSITES, FRACTURE...

A NASTRAN model of a UH-1B tail boom that had been designed for another project was used to investigate the effect on structural integrity of simulated projectile damage. Elements representing skin, and sections of stringers, longerons and bulkheads were systematically deleted to represent projectile damage. The structure was loaded in a manner to represent the flight loads that would be imposed on the tail boom at a 130 knot cruise. The deflection of four points on the rear of the tail boom...

Topics: NASA Technical Reports Server (NTRS), DAMAGE ASSESSMENT, FINITE ELEMENT METHOD, IMPACT DAMAGE,...