crossings. The results of the service test series are statistically evaluated and presented as stress/life curves for SAE 5140 and for 2024 T 3 specimens. The corresponding stress/life curves, obtained in service duplication tests were not significantly different. However, the conventional eight-step program tests overestimate the fatigue life observed in service and service duplication tests by a factor which may be as high as five. The results of the test series were also compared to fatigue calculations. It was found that the application of a modified linear fatigue damage rule, which does not account for the sequence effect of load changes, yielded fatigue life data which are very much on the nonconservative side. This confirmed the now generally accepted fact that yield fatigue life prediction models must account for the sequence of individual peaks and troughs. Author N79-33498# Technische Hogeschool, Delft (Netherlands). PREDICTION METHODS FOR FATIGUE CRACK GROWTH IN AIRCRAFT MATERIAL J. Schijve Jun. 1979 44 p refs Presented at the 12th Natl. Symp. on Fracture Mech., 21-23 May. St. Louis; sponsored by ASTM (LR-282; ICAF-1100) Avail: NTIS HC A44/MF A01 A survey is given of relevant knowledge on fatigue crack growth and qualitative and quantitative understanding of predictions. Aspects of cycle-by-cycle predictions and characteristic K prediction methods are discussed. Prediction problems are covered including: (1) crack growth under flight-simulation loading with crack closure measurements; (2) predictions for flightsimulation loading based on a constant crack opening stress level; and (3) crack growth under pure random loading with different s sub rms-values, two irregularities, and two crest factors. Random load tests carried out to explore the usefulness of K sub rms are discussed. J.M.S. N79-33499*# National Aeronautics and Space Administration. The basic problem of how to simply represent a curved web of a spar in a finite element structural model was addressed. The ratio of flat web to curved web axial deformations and longitudinal rotations were calculated using NASTRAN models. Multiplying factors were developed from these calculations for various web thicknesses. These multiplying factors can be applied directly to the area and moment of inertia inputs of the finite element model. This allows the thermal stress relieving configurations of sine wave and circular arc webs to be simply accounted for in finite element structural models. Author N79-33500*# National Aeronautics and Space Administration. LOAD CONCENTRATION DUE TO MISSING MEMBERS IN A large space structure with members missing was investigated using a finite element analysis. The particular structural configuration was the tetrahedral truss, with attention restricted to one of its planar faces. Initially the finite element model of a complete face was verified by comparing it with known results for some basic loadings. Then an analysis was made of the structure with members near the center removed. Some calculations were made on the influence of the mesh size of a structure containing a hexagonal hole, and an analysis was also made of a structure with a rigid hexagonal insert. In general, load concentration effects in these trusses were significantly lower than classical stress concentration effects in an infinitely wide isotropic plate with a circular rigid inclusion, although larger effects were obtained when a hole extended over several rings of elements. Author COMPUTER TECHNIQUES FOR PLASTICITY H. Armen and A. Pifko Jun. 1979 50 p refs (AD-A070810; RM-688J) Avail: NTIS HC A03/MF A01 CSCL 20/11 Implicit in the development of any plasticity model are assumptions associated with the behavior of the actual material. Assumptions generally employed are listed with a discussion of their implications. Several models that incorporate these assumptions or attempt to overcome their restrictions are presented. Several alternative algorithms have evolved and are currently being used in finite element programs for plastic analysis. Each of these has computational advantages and liabilities so that the analyst is presented with choices among acceptable procedures. These procedures are reviewed in order to facilitate a rational selection among competing procedures that best suit the needs of a particular problem class. The contents of this memorandum will appear as a chapter in the ASME Pressure Vessel and Piping Division Vol. I Decade of Progress in Design and Analysis (1980). GRA . This final report covers the theoretical development of and experimental results for the stress analysis and strength characterization of thick composite laminates. Thick composite laminates (consisting of 38 plies or more) are being evaluated for use in future high performance anti-ballistic missiles and other aerospace applications. The theoretical development includes the derivation of a high-order theory of plate deformation which accounts for the effects of transverse shear deformation, transverse normal strain, and a non-linear distribution of the in-plane displacements with respect to the thickness coordinates. The theory is developed for both homogeneous and laminated plates. Further examination of this high-order plate theory via stress solutions which have been carried out to assess its accuracy is reported. This theory, in effect, enables close estimation of three-dimensional stress components from essentially twodimensional analysis. The effects of the three-dimensional state of stress on the strength of thick laminates are analysed with a 3-D failure criterion. The tensor polynomial method is extended with full account given to three-dimensional stress state effects and is presented together with experiment and evaluation of the coefficients. GRA Generalized derivatives of fractional order are used to construct stress-strain constitutive relations for viscoelastic materials, based on the observed sinusoidal behavior of the materials. The non-periodic behavior of one material is observed in the laboratory and compares favorably with the non-periodic behavior of the material predicted by its generalized derivative constitutive relation. Having established that the generalized derivative constitutive relation is an appropriate mathematical model for the general motion of at least one viscoelastic material. the tools for the analysis of structures of engineering interest are put forward. In particular, attention is focused on a finite element formulation of, and solutions to the equations of motion for structures containing elastic and viscoelastic components. Author (GRA) N79-33504# McDonnell Aircraft Co., St. Louis, Mo. ENVIRONMENT LOAD INTERACTION EFFECTS ON CRACK GROWTH Final Report, Jul. 1976 - Aug. 1978 H. D. Dill and C. R. Saff Nov. 1978 224 p refs The objective of this program was to systematically investigate chemical environment-load interaction effects on crack propagation. The program was focused by developing a set of design guidelines and criteria for a durability and damage tolerance control plan for landing gear. Current life prediction capability was assessed by comparison of prediction and test. A field survey was conducted to catalog the size, type, and locations of flaws in landing gear components. A crack growth prediction capability developed through analysis and test accounts for environment and load interaction effects. Materials studied are HP-9 Ni-4Co-30 and 300M steels, and 7075-T6 and 7049-T73 aluminums. A flight-by-flight test stress history was developed for a landing gear component, and crack growth predictions prepared. Subsequently, spectrum tests were performed. A Durability/ Damage Tolerance Control Plan for landing gear is outlined. A problem of interest to the Air Force is the design of acoustically sound aircraft structural components. This is because sonic fatigue failures have resulted in unacceptable maintenance and inspection burdens associated with the operation of the aircraft. In some instances, sonic fatigue failures have resulted in major redesign efforts of structural components. Currently, the sonic fatigue design methods are based upon a combination of experimental and analytical techniques. The analytical methods are based on the linear or small deflection theory (Sonic Fatigue Design Guide for Military Aircraft, AFFDL-TR-74-112, for example). But, on the contrary, the test structural panels respond nonlinearly with large deflections at high intensity acoustic pressure levels. This large amplitude geometrical nonlinearity is the major factor that causes disagreement between the computed and the measured random responses. To improve the analytical design methods, large deflection or nonlinear structure theory must be employed in the analysis. This report presents a review of existing analytical and numerical methods on random excitation on nonlinear multi-degree-of-freedom systems, and an evaluation of these methods based on some realistic considerations from the point of view of their application to complex panel configurations of aircraft structure. GRA The details of a study to experimentally determine the strain and deflection profile induced in a uniformly loaded, simply supported 1.1-m x 2.3-m aluminum-skin Kraft-paper-honeycombcore sandwich panel are documented. Twelve panels typical of the type used in military rigid wall tactical shelters were tested at loadings up to 70 kPa. The experimental procedure and apparatus, including a special vacuum chamber constructed to stress the large panels, are described as well as details of the various panels tested. The effects of loading arrangement, strain gage transverse sensitivity and adhesive joint location are addressed. Panel strain and deflection data and core shear data are presented. GRA In conventional approaches to finite element stress analysis, accuracy is obtained by fixing the degree p of the approximating polynomial and by allowing the maximum diameter h of elements in the triangulation of approach zero. An alternate approach is to fix the triangulation and to increase the degree of approximating polynomials in those elements where more accuracy is necessary to have a family of finite elements of arbitrary polynomial degree p with the property so that as much information as possible can be retained from the pth degree approximation when computing the (p/l) st degree approximation. Comparison of the optimal beam (a variable-section beam) with a reference beam (a constant-section beam) shows that the weight reduction depends strongly on the frequency parameter beta. This weight reduction is negligible for beta approaching O, is 11.3 per cent for beta 1, is 55.3 per cent for beta = 1.4, and approaches 100 per cent for beta approaching 90 degrees. GRA = A review is presented of B, C and K stress indexes used in the ASME Nuclear Power Plant Code for girth butt welds and girth fillet welds. Theoretical stresses are presented to aid in evaluating C-indexes. Fatigue test data are presented to aid in evaluating K-indexes and CK-products. A limit load theory is presented to aid in evaluating B-indexes. As a result of this review, recommendations are made for changes in the ASME Code. A major part of this consists of presenting definitions for girth welded joints and transitions and appropriate stress indexes for those joints. DOE Stress concentration is studied by means of structural calculations using the integral equation method. Problems related to the discontinuity of the stress vector are resolved by introducing double points, which also permits a coupling of the finite element method with the integral equation calculation method. The integral equation method, developed for the elasticity case, is extended to the elastoviscoplasticity case by means of a process of step by step linearization in time. The proposed method is valid for any constitutive law expressing the rate of viscoplastic strain in terms of the values of the viscoplastic strain, the stress, and one or more implicit parameters. A practical approximation method is developed that allows the time variation of the maximum stress at the bottom of the notch to be predicted in a simple manner. Some examples are given and the results are compared with those obtained by other methods of calculation (finite element method and exact analytic solutions) and by some experimental studies. Author (ESA) Various methods of concrete testing, including flexural strength from beam breaks, compressive strength and splitting tensile strength from cylinders, and penetration resistance from steel probes, were evaluated both under controlled laboratory and partially controlled field conditions. Laboratory results provided good correlation for all methods considered, while the results derived from partially controlled field tests deviated somewhat from confidence bands established on the basis of laboratory data. Penetration-resistance and splitting-tensile tests are recommended as an alternate to beam breaks for concretes with specific constituents for use in determining when forms can be removed from, or loads applied to concrete structures subject to bending stresses. GRA N79-33514# California Univ., Richmond. Earthquake Engineering Research Center. The model is constructed using system identification. The process consists of selecting a form for the model, and then using suitable mathematical techniques to adjust the numerical coefficients within it so that reproduces as closely as possible the results of experiments. The response of reinforced concrete members to large cyclic loads is nonlinear and inelastic and it changes throughout the history of the load. Because it is so complicated, the physical behavior of the material and mechanics which underlie it are investigated. A model form is then selected which divides the member into hypothetical layers. The material in each layer obeys an appropriate nonlinear constitutive law and the number forces are derived by integration across the cross section. GRA Information is given on earth photographs obtained by the Apollo astronauts during the Apollo Soyuz Test Project. The data are arranged in three sections. A map index shows the boundaries of each photograph and is used for a quick survey of the coverage for a given geographical area. A tabular index provides the following data: list of photographs by serial number, description of geographic location, latitude and longitude of the center point of the photograph, date when photograph was taken, ground elapsed time, revolution number of Apollo spacecraft, approximate spacecraft altitude, tilt, sun angle, camera, and lens. The photographic index provides same size black and white prints made from the original color negatives. A.W H. N79-33525*# Centre National d'Etudes Spatiales, Paris (France). SEA SURFACE TEMPERATURE OF THE COASTAL ZONES OF FRANCE P. Y. Deschamps (Lille Univ., France), M. Crepon (Museum National d'Histoire Naturelle, France), J. M. Monget (Ecole National Superieure des Mines de Paris), and F. Verger, Principal Investigators (Ecole Normale Superieure, France) Aug. 1979 39 p Sponsored by NASA Original contains imagery. Original photography may be purchased from the EROS Data Center, Sioux Falls, S. D. 57198 ERTS (E79-10293; NASA-CR-162324) HC A03/MF A01 CSCL 08J Avail: NTIS N79-33527*# (Contract NAS5-24316) (E79-10295; NASA-CR-162326; HC A02/MF A01 CSCL 08H 10 Oct. 1979 5 P There are no author-identified significant results in this report. The effects of vegetation canopy structure on thermal infrared sensor response must be understood before vegetation surface temperatures of canopies with low percent ground cover can be accurately inferred. The response of a sensor is a function of vegetation geometric structure, the vertical surface temperature distribution of the canopy components, and sensor view angle. Large deviations between the nadir sensor effective radiant temperature (ERT) and vegetation ERT for a soybean canopy were observed throughout the growing season. The nadir sensor ERT of a soybean canopy with 35 percent ground cover deviated from the vegetation ERT by as much as 11 C during the mid-day. These deviations were quantitatively explained as a function of canopy structure and soil temperature. Remote sensing techniques which determine the vegetation canopy temperature(s) from the sensor response need to be studied. A.R.H. N79-33531*# National Aeronautics and Space Administration. Goddard Space Flight Center, Greenbelt, Md. AN IMPROVED SCHEME FOR THE REMOTE SENSING OF SEA SURFACE TEMPERATURE G. Dalu (CNR, Ist. di Fisica della Atmosfera, Rome). C. Prabhakara, R. C. Lo (Computer Sci. Corp., Silver Spring, Md.), and M. J. Mack (Computer Sci. Corp., Silver Spring, Md.) Jul. 1979 29 p refs (NASA-TM-80332) Avail: NTIS HC A03/MF A01 CSCL 08J A radiometer which possesses two channels in the 11 to 13 micrometer window region is discussed. The radiometer is used to estimate the sea surface temperature within an accuracy of 1 C. A mathematical model is presented to show that the accuracy is improved to within 0.3 C with an independent estimate of total precipitable water vapor. A broadband channel in the 18 micrometer water vapor band is introduced in addition to the two former channels to remotely sense the total precipitable water vapor. The effect of the surface emissivity is taken into account in the scheme. A.W.H. N79-33532# Purdue Univ., Lafayette, Ind. School of Electrical Engineering. (AD-A071793; ARO-13444.2) Avail: NTIS HC A09/MF A01 CSCL 02/6 A thermal canopy signature model (TCSM) was developed to approximate the thermal behavior of a vegetation canopy by a mathematical abstraction of three horizontal layers of vegetation. Canopy geometry within each layer is quantitatively described by the foliage and branch orientation distributions. Canopy geometry, solar irradiance, air temperature. horizontal wind velocity, relative humidity, and ground temperature are used to calculate the energy budgets of average leaves within each layer The resulting system of conservation equations is solved for the average layer temperature. This information, together with the angular distributions of radiating elements, is then used to calculate the thermal existance as a function of view angle above the canopy. Optical diffraction techniques were developed and employed to measure canopy geometry. Solar radiation absorption with the vegetation terrain elements is calculated using a modification of a Monte Carlo model (SRVC) developed for the reflective energy regime. The models were applied to a lodgepole pine (Pinus contorta) canopy and the results for a diurnal cycle are validated with radiometric measurements. Simulated versus measured radiometric average temperatures of Layer 2 correspond approximately within two degrees centigrade. Simulated results suggest that canopy geometry can significantly influence the effective radiant temperature recorded by a sensor above the canopy as a function of view angle. GRA N79-33534# Army Cold Regions Research and Engineering Lab., Hanover, N. H. SNOWPACK OPTICAL PROPERTIES IN THE INFRARED Roger H. Berger May 1979 16 p refs (DA Proj. 4A7-62730-AT-42) (AD-A071004; CRREL-79-11) Avail: NTIS HC A02/MF A01 CSCL 08/12 A theory of the optical properties of snow in the 2-20 microns region of the infrared has been developed. Using this theory it is possible to predict the absorption and scattering coefficients and the emissivity of snow, as a function of the snow parameters of grain size and density, for densities between 0.17 and 0.4 g/cu. cm. The absorption and scattering coefficients are linearly related to the density and inversely related to the average grain size. The emissivity is independent of grain size and exhibits only a weak dependence upon density. GRA |