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NASA NTRS1987

Large-scale Advanced Prop-fan (LAP) static rotor test report

Discussed is Static Rotor Testing of the SR-7L Large Scale Advanced Prop-Fan (LAP). The LAP is an advanced 9 foot diameter, 8 bladed propeller designed and built by Hamilton Standard under contract to the NASA Lewis Research Center. The Prop-Fan employs thin swept blades to provide efficient propulsion at flight speeds up to Mach .85. Static Testing was conducted on a 10,000 HP whirl rig at Wright Patterson Air Force Base. The test objectives were to investigate the Prop-Fan static aerodynamic and structural dynamic performance, determine the blade steady state stressers and deflections and to measure steady and unsteady pressures on the SR-7L blade surface. The measured performance of the LAP correlated well with analytical predictions at blade pitch angles below 30 deg. A stall buffet phenomenon was observed at blade pitch angles above 30 deg. This phenomenon manifested itself by elevated blade vibratory stress levels and lower than expected thrust produced and power absorbed by the Prop-Fan for a given speed and blade angle.

Degeorge, Charles L.↗

NASA NTRS1991

Measurements of fuselage skin strains and displacements near a longitudinal lap joint in a pressurized aircraft

Strains and displacements in a small area near a longitudinal lap joint in the fuselage skin of a B737 aircraft were measured during a pressurization cycle to a differential pressure of 6.2 psi while the aircraft was on the ground. It was found that hoop strains were higher than longitudinal strains at each location; membrane strains in the unreinforced skin were higher than in the joint; membrane strains in the hoop direction, as well as radial displacements, tended to be highest at the mid-bay location between skin reinforcements; significant bending in the hoop direction occurred in the joint and in the skin near the joint, and the bending was unsymmetrically distributed about the stringer at the middle of the joint; and radial displacements were unsymmetrically distributed across the lap joint. The interpretation of the strain gage data for locations on the bonded and riveted lap joint assumed that the joint did not contain disbonded areas.

Phillips, Edward P.↗

NASA NTRS1991

Preliminary results on the fracture analysis of multi-site cracking of lap joints in aircraft skins

This paper presents results of a fracture mechanics analysis relevant to fatigue crack growth at rivets in lap joints of aircraft skins are presented. Multi-site damage (MSD) is receiving increased attention within the context of problems of aging aircraft. Fracture analyses previously carried out include small-scale modeling of rivet/skin interactions, larger-scale two-dimensional models of lap joints similar to that developed here, and full scale three-dimensional models of large portions of the aircraft fuselage. Fatigue testing efforts have included flat coupon specimens, two-dimensional lap joint tests, and full scale tests on specimens designed to closely duplicate aircraft sections. Most of this work is documented in the proceedings of previous symposia on the aging aircraft problem. The effect MSD has on the ability of skin stiffeners to arrest the growth of long skin cracks is a particularly important topic that remains to be addressed. One of the most striking features of MSD observed in joints of some test sections and in the joints of some of the older aircraft fuselages is the relative uniformity of the fatigue cracks from rivet to rivet along an extended row of rivets. This regularity suggests that nucleation of the cracks must not be overly difficult. Moreover, it indicates that there is some mechanism which keeps longer cracks from running away from shorter ones, or, equivalently, a mechanism for shorter cracks to catch-up with longer cracks. This basic mechanism has not been identified, and one of the objectives of the work is to see to what extent the mechanism is revealed by a fracture analysis of the MSD cracks. Another related aim is to present accurate stress intensity factor variations with crack length which can be used to estimate fatigue crack growth lifetimes once cracks have been initiated. Results are presented which illustrate the influence of load shedding from rivets with long cracks to neighboring rivets with shorter cracks. Results will also be included for the effect of residual stress due to the riveting process itself. All the results presented in this paper should be regarded as preliminary in the sense that further work by ourselves and others will be required to validate them and to establish their sensitivity to more embellished modelling assumptions.

Aging Aircraft↗

NASA NTRS1998

Methodology for Predicting the Onset of Widespread Fatigue Damage in Lap-Splice Joints

NASA has conducted an Airframe Structural Integrity Program to develop the methodology to predict the onset of widespread fatigue damage to lap-splice joints of fuselage structures. Several stress analysis codes have been developed or enhanced to analyze the lap-splice-joint configuration. Fatigue lives in lap-splice-joint specimens and fatigue-crack growth in a structural fatigue test article agreed well with calculations from small-crack theory and fatigue-crack growth analyses with the FASTRAN code. Residual-strength analyses of laboratory specimens and wide stiffened panels were predicted quite well from the critical crack-tip-opening angle (CTOA) fracture criterion and elastic-plastic finite-element analyses (two- or three-dimensional codes and the STAGS shell code).

Newman, J. C., Jr.↗

NASA NTRS2000

Residual Strength Analyses of Riveted Lap-Splice Joints

The objective of this paper was to analyze the crack-linkup behavior in riveted-stiffened lap-splice joint panels with small multiple-site damage (MSD) cracks at several adjacent rivet holes. Analyses are based on the STAGS (STructural Analysis of General Shells) code with the critical crack-tip-opening angle (CTOA) fracture criterion. To account for high constraint around a crack front, the "plane strain core" option in STAGS was used. The importance of modeling rivet flexibility with fastener elements that accurately model load transfer across the joint is discussed. Fastener holes are not modeled but rivet connectivity is accounted for by attaching rivets to the sheet on one side of the cracks that simulated both the rivet diameter and MSD cracks. Residual strength analyses made on 2024-T3 alloy (1.6-mm thick) riveted-lap-splice joints with a lead crack and various size MSD cracks were compared with test data from Boeing Airplane Company. Analyses were conducted for both restrained and unrestrained buckling conditions. Comparison of results from these analyses and results from lap-splice-joint test panels, which were partially restrained against buckling indicate that the test results were bounded by the failure loads predicted by the analyses with restrained and unrestrained conditions.

Seshadri, B. R.↗

NASA NTRS2004

Petrography of Lunar Meteorite LAP 02205, a New Low-Ti Basalt Possibly Launch Paired with NWA 032

Lunar meteorite LAP 02205 is a 1.23 kg basalt collected during the 2002 field season in the La- Paz ice field, Antarctica [1]. We present a petrographic description including mineral modes and compositions, and the major-element composition of the bulk meteorite. LAP 02205 is an Fe-rich, moderately low-Ti mare basalt that is similar in composition, mineralogy, and mineral chemistry to the NWA 032 basaltic lunar meteorite. LAP 02205 is yet another of the moderately low- Ti basaltic meteorites that are underrepresented among Apollo and Luna samples but that appear from remote sensing to be the most common basalt type on the Moon.

Jolliff, B. L.↗

NASA NTRS2004

Global-Local Finite Element Analysis of Bonded Single-Lap Joints

Adhesively bonded lap joints involve dissimilar material junctions and sharp changes in geometry, possibly leading to premature failure. Although the finite element method is well suited to model the bonded lap joints, traditional finite elements are incapable of correctly resolving the stress state at junctions of dissimilar materials because of the unbounded nature of the stresses. In order to facilitate the use of bonded lap joints in future structures, this study presents a finite element technique utilizing a global (special) element coupled with traditional elements. The global element includes the singular behavior at the junction of dissimilar materials with or without traction-free surfaces.

Kilic, Bahattin↗

NASA NTRS2012

Nonlinear Analysis of Bonded Composite Tubular Lap Joints

The present study describes a semi-analytical solution method for predicting the geometrically nonlinear response of a bonded composite tubular single-lap joint subjected to general loading conditions. The transverse shear and normal stresses in the adhesive as well as membrane stress resultants and bending moments in the adherends are determined using this method. The method utilizes the principle of virtual work in conjunction with nonlinear thin-shell theory to model the adherends and a cylindrical shear lag model to represent the kinematics of the thin adhesive layer between the adherends. The kinematic boundary conditions are imposed by employing the Lagrange multiplier method. In the solution procedure, the displacement components for the tubular joint are approximated in terms of non-periodic and periodic B-Spline functions in the longitudinal and circumferential directions, respectively. The approach presented herein represents a rapid-solution alternative to the finite element method. The solution method was validated by comparison against a previously considered tubular single-lap joint. The steep variation of both peeling and shearing stresses near the adhesive edges was successfully captured. The applicability of the present method was also demonstrated by considering tubular bonded lap-joints subjected to pure bending and torsion.

E. Oterkus↗

NASA NTRS1972

A fracture mechanics analysis of adhesive failure in a single lap shear joint.

Discussion of adhesive fracture of single lap shear joints in terms of a maximum stress criterion and an energy balance. The Goland and Reissner (1944) analysis is used to determine the stress distribution in the adhesive assembly, and the results obtained are introduced into an energy balance to determine the initiation of adhesive fracture. In the stress analysis the loads at the edges of the joint are first determined. This is a problem in which the deformation of the joint sheets must be taken into account and is solved by using the finite-deflection theory of cylindrically bent plates. Then the stress in the joint due to applied loads is determined. This problem is formulated as one in plane strain consisting of two rectangular sheets of equal thickness and unit width. With the aid of this stress analysis and the stresses obtained from the conditions of equilibrium the contributions to the energy change with crack length are calculated. The analysis performed is then compared with a maximum stress criterion for a lap joint.

Devries, K. L.↗

NASA NTRS1978

Determination of bulk diffusion lengths for angle-lapped semiconductor material via the scanning electron microscope: A theoretical analysis

A standard procedure for the determination of the minority carrier diffusion length by means of a scanning electron microscope (SEM) consists in scanning across an angle-lapped surface of a P-N junction and measuring the resultant short circuit current I sub sc as a function of beam position. A detailed analysis of the I sub sc originating from this configuration is presented. It is found that, for a point source excitation, the I sub sc depends very simply on x, the variable distance between the surface and the junction edge. The expression for the I sub sc of a planar junction device is well known. If d, the constant distance between the plane of the surface of the semiconductor and the junction edge in the expression for the I of a planar junction is merely replaced by x, the variable distance of the corresponding angle-lapped junction, an expression results which is correct to within a small fraction of a percent as long as the angle between the surfaces, 2 theta sub 1, is smaller than 10 deg.

Vonroos, O.↗

NASA NTRS1979

A critical examination of stresses in an elastic single lap joint

The results of an approximate nonlinear finite-element analysis of a single lap joint are presented and compared with the results of a linear finite-element analysis, and the geometric nonlinear effects caused by the load-path eccentricity on the adhesive stress distributions are determined. The results from finite-element, Goland-Reissner, and photoelastic analyses show that for a single lap joint the effect of the geometric nonlinear behavior of the joint has a sizable effect on the stresses in the adhesive. The Goland-Reissner analysis is sufficiently accurate in the prediction of stresses along the midsurface of the adhesive bond to be used for qualitative evaluation of the influence of geometric or material parametric variations. Detailed stress distributions in both the adherend and adhesive obtained from the finite-element analysis are presented to provide a basis for comparison with other solution techniques.

Cooper, P. A.↗

NASA NTRS1979

An analysis of interface crack in adhesively bonded lap shear joints

This paper presents an analytical study of interface crack problems in adhesively bonded lap shear joints. A convenient and accurate method of analysis is developed on the basis of conservation laws in elasticity and of the fundamental relationships in fracture mechanics of interface crack problems. The problem is eventually reduced to a system of linear algebraic equations of mixed-mode stress intensity factor solutions. One of the salient features of the present approach is that the interface crack-tip stress intensity solutions can be determined accurately and directly by the information extracted from the far field. Solutions of the interface crack problems in lap shear joints have been obtained for the cases of various adhesive/adherend material systems and geometric configurations of the crack and the joint. Of particular interest is the evaluation of the mixed-mode stress intensity factors and the associated energy release rates. They are determined explicitly to illustrate the fundamental nature of the joint fracture problem.

Wang, S. S.↗

NASA NTRS1980

Analysis and test of bonded single lap joints with preformed adherends

A theoretical and experimental study has been conducted to investigate the load transfer of a single lap joint where the adherends have been preformed so that the angle between the line of action of the applied in-plane force and the bond line is reduced. The preforming of the adherend reduces the moment resultant in the adherend at the edge of the overlap region which reduces both the maximum peel and shear stresses in the adhesive, and gives a more uniform shear distribution in the adhesive. An increase in static load transfer of up to 120 percent has been shown, and several orders of magnitude increase in fatigue life have been achieved with modest preform angles. Thus, sizeable benefits can be obtained in the fatigue life or additional load capacity of bonded single lap joints by preforming the adherends.

Sawyer, J. W.↗

NASA NTRS1981

Analysis of interface cracks in adhesively bonded lap shear joints, part 4

Conservation laws of elasticity for nonhomogeneous materials were developed and were used to study the crack behavior in adhesively bonded lap shear joints. By using these laws and the fundamental relationships in fracture mechanics of interface cracks, the problem is reduced to a pair of linear algebraic equations, and stress intensity solutions can be determined directly by information extracted from the far field. The numerical results obtained show that: (1) in the lap-shear joint with a given adherend, the opening-mode stress intensity factor, (K sub 1) is always larger than that of the shearing-mode (K sub 2); (2) (K sub 1) is not sensitive to adherent thickness abut (K sub 2) increases rapidly with increasing thickness; and (3) (K sub 1) and (K sub 2) increase simultaneously as the interfacial crack length increases.

Wang, S. S.↗

NASA NTRS1982

Interface cracks in adhesively bounded lap-shear joints

A study on the elastic behavior of interface cracks in adhesively bonded lap-shear joints is presented. The problem is investigated by using a recently developed method of analysis based on conservation laws in elasticity for nonhomogeneous solids and fundamental relationships in fracture mechanics of dissimilar materials. The formulation leads to a pair of linear algebraic equations in mixed-mode stress intensity factors. Singular crack-tip stress intensity solutions are determined directly by information extracted from the far field. Stress intensity factors and associated energy release rates are obtained for various cases of interest. Fundamental nature of the interfacial flaw behavior in lap-shear adhesive joints is examined in detail.

Wang, S. S.↗

NASA NTRS1983

Material characterization of structural adhesives in the lap shear mode

A general method for characterizing structual adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semiempirical and theoretical approaches are used. The semiempirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Two different model adhesives are used in the single lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.

Sancaktar, E.↗

NASA NTRS1983

Material characterization of structural adhesives in the lap shear mode

A general method for characterizing structural adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semi-empirical and theoretical approaches are used. The semi-empirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Three different model adhesives are used in the simple lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.

Schenck, S. C.↗

NASA NTRS1985

Large-scale Advanced Propfan (LAP) program

The propfan is an advanced propeller concept which maintains the high efficiencies traditionally associated with conventional propellers at the higher aircraft cruise speeds associated with jet transports. The large-scale advanced propfan (LAP) program extends the research done on 2 ft diameter propfan models to a 9 ft diameter article. The program includes design, fabrication, and testing of both an eight bladed, 9 ft diameter propfan, designated SR-7L, and a 2 ft diameter aeroelastically scaled model, SR-7A. The LAP program is complemented by the propfan test assessment (PTA) program, which takes the large-scale propfan and mates it with a gas generator and gearbox to form a propfan propulsion system and then flight tests this system on the wing of a Gulfstream 2 testbed aircraft.

Sagerser, D. A.↗