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Simple calculations for determining estimated extremes in fatigue life of metals with or without accounting for cycle dependent hardening, softening and mean stress relaxation in fatigue analysis, are presented. These calculations aid in assessing the importance of cyclic deformation properties in cumulative damage procedures. An SAE 1045 quenched and tempered steel is considered for illustration. In general cycle dependent deformation phenomena may be important only in intermediate and long life situations. The sensitivity of predicted life to cyclic hardening or softening depends on the degree of hardening or softening a material exhibits, whereas in the case of mean stress relaxation it depends on the shape of the cyclic stress-strain curve or the strain hardening exponent. However the need for a proper accounting of cyclic history, recognized as the 'cycle counting problem' in fatigue literature, is the most important requisite of a cumulative damage analysis. Two alternative approaches of dealing with the cycle counting problem are discussed.

Nemo Model 2000 acrylic plastic pressure hull assembly is described and represents the latest addition to the Nemo hull series represented by Nemo Model 600 and 1000 hull assemblies. The 66 inch OD x 58 inch ID spherical acrylic hull with aluminum hatches has successfully withstood 24 hour long external hydrostatic pressurizations to 450, 900, 1340 and 1800 psi. Pressure cycling and short term destructive testing of 15 inch OD x 13 inch ID scale models has shown that the crackfree fatigue life is in excess of 1000 pressure cycles at depths to 3000 feet and the short term implosion pressure is in the range of 10,000 to 11,000 feet. Stress wave emissions have been found to be a good indicator of incipient failure.

A laboratory fatigue test was performed on an E-2 fuselage to determine if it could sustain the effects of 3000 arrested landings and 4000 catapult launches. The right-hand keel beam failed after 4556 catapult test cycles. Using a test scatter factor of 2, this is equivalent to 2278 service catapult launches. The keel beam was repaired and modified and testing was continued until a total of 8000 catapult test cycles had been applied.

Adhesively bonded joints were failed statically and in fatigue to test the validity of a fatigue life assessment model. The results of the tests were in agreement with both the assumptions and the predictions of the model. In particular, the failure mode was constant for all tests and the observed static strength and fatigue lives were adequately modeled by the Weibull family of distributions with constant, but different, shape parameters over the range of test conditions considered. The predicted relationship between the shape parameters as a function of an experimentally determined material property was observed. The predicted distribution of residual strength as a function of time in the fatigue environment was verified and agreement between prediction and observation for an accelerated fatigue test was obtained., GIDEP-347.40.00.00-G7-05.

S-N curves are derived for aluminum wing and tail structures by fitting various regression models to 246 full-scale constant-amplitude fatigue test results from twelve types of aircraft structures. The derived curves were tested by comparing the predicted lives with actual test results of various aircraft structures fatigue tested to variable-amplitude loads spectra. More reliable predictions resulted from these derived S-N curves than from existing S-N curves., ISSN 0077-5541.

The objective of this research program was to investigate the influence of various parameters on the fatigue life of wire rope through well controlled and statistically planned laboratory bend-over-sheave fatigue experiments. Parameters studied included three operating loads for ropes subjected to both simple single-sheave bending and two-sheave reverse bending. A total of 288 rope specimens were cycled to failure, and the results were analyzed statistically to determine which parameters had a significant influence on rope life.

The objectives of this program were to study the effects of aluminum and zinc metal substrates with a passive overcoat on the corrosion fatigue life of HY 130 in a marine environment and to develop a shipboard repair process for hydrofoil strut and foil external coatings. Conclusions were reached about the effectiveness of the active metal substrates in protecting HY 130. A repair material and procedure were recommended. (Author), HYSTU Plan Number 303.

A reliability analysis for predicting the statistical distribution of time to fatigue crack initiation for aircraft structures in service is presented. The present analysis uses the statistical data of the specimen fatigue tests, the full-scale structure tests, and the statistical dispersion of aircraft service loads. The statistical distribution of the fatigue performance of the full-scale structure under laboratory loading spectrum is assumed to be Weibull. The service loads for gust turbulences are modeled as Poisson processes for transport-type aircraft while the maneuver loads are modeled as compound Poisson processes for fighter and training aircrafts.

This report describes an approach for obtaining ultimate tensile design allowables which should result in satisfactory fatigue performance. Thus, fatigue considerations can be included in the original design rather than being checked as an afterthought after the design has been set. This can avoid costly redesigns to obtain structural integrity in fatigue., See also volume 1, AD/A-003 649 and volume 3, AD/A-003 651.

This paper reviews recently developed methods for metal lifetime prediction at elevated temperatures. These methods can be categorized as either (a) Parametric, (b) Damage Summation, (c) Strainrange Partitioning, or (d) Frequency Modification. The capabilities and limitations of these various approaches are discussed and the problem of extrapolation beyond laboratory experience is considered., Pub. in AGARD Conference Proceedings No. 155. Specialists Meeting on Low Cycle High Temperature Fatigue. Meeting of the Structures and Materials Panel (38th), Washington, D.C., 21-26 Apr 74, p6-1 - 6-16 1974.

The Hysteresis fatigue Analysis (HFA) method uses a cyclic stress-strain curve in conjunction with a Neuber analyses to describe a notch stress-strain history. The notch stresses are then used in a damage theory which employs an equivalent stress. The HFA does not incorporate a model of cyclic stress relaxation. The purpose of the current effort is to ascertain if, without such a model, the HFA is capable of predicting a series of test results for 7075-T6 aluminum performed by J. Schijve and F. P. Jacobs. This is accomplished by comparing the predictions from the HFA to test results. The HFA predictions are then compared to predictions of the same test lives using the Sequence Accountable Fatigue Program (SAF) developed by Potter. Potter's program employs a decay function which relaxes residual stresses as a function of cycles. To ascertain if the differences in the two fatigue life prediction methods could possibly be attributed to relaxation, a parametric study was made. This paper describes the results of that study.

The analytical characterization of a multilayer fiber composite plate (without hole) was accomplished for both static and dynamic loading conditions using the finite difference technique. Thornel 300/5208 composites with and without holes were subjected to static and tensile fatigue testing. Five fiber orientations were submitted to test. Tensile fatigue testing also included three loading conditions and two frequencies. The low-cycle test specimens demonstrated a shorter tensile fatigue life than the high-cycle test specimens. Failure surfaces demonstrated effect of testing conditions. Secondary failure mechanisms, such as: delamination, fiber breakage, and edge fiber delamination were present in (01/+ or -45/0) sub s and (0/+ or -60/0) sub s specimens. Longitudinal delamination between plies also occurred in these specimens. (MM)

The fatigue crack initiation lives of annealed Ti-6Al-4V alloys were determined at low (+ or - 0.006 in/in) and high (+ or - 0.012 in/in) shear strain amplitudes. The initiation life was separated from the propagation life by determining when extensive axial elongation of the specimen occurred. At 0.006 and 0.012 strain amplitudes the a-b annealed (alpha beta A) and mill annealed (MA) specimens have similar lives to crack initiation followed by recrystallized anneal (RA) and beta annealed (beta A) specimens. Analysis of the beta A specimens showed that structure related fatigue fracture was occurring and this was not observed with the other anneals. 'Cyclic creep' tests were conducted on each anneal treatment and the RA material exhibited the best dimensional stability and the beta A material the worst. These results are in accordance with the expected phase stability of each alloy; the RA material should be the closest to an equilibrium microstructure; the Beta A material the farthest from an equilibrium microstructure. The greatest increase in fatigue lives occurred for specimens quenched from a solution temperature of 1650 F, which is about 100 F below the beta transus. Reduction of solution temperature to 1550 F, or increases to 1750 F and 1950 F resulted in lower lives than the 1650 F solution temperature. The fracture surface of the material quenched from 1950 F had brittle type fatigue striations, also the region of fast fracture had evidence of microstructure effects. (Author)

Rolling contact fatigue studies were conducted comparing hot-pressed silicon nitride and consumable vacuum melted M-50 steel. Test results showed that: (a) Silicon nitride is superior to M-50 steel by at least an order of magnitude. (b) Surface finishing process significantly effects the fatigue life of silicon nitride. (c) Silicon nitride run in contact with M-50 steel may have a detrimental effect on the fatigue life of M-50 steel. (d) Skidding may be detrimental to the surface durability of silicon nitride. (Author), See also report dated Oct 73, AD-771 393.

Fatigue crack initiation (Stage 1) and Fatigue crack propagation (Stage 11) periods in a given fatigue life can be determined by an indirect testing method. This method is based on a series of two level strain tests in which each axial specimen is strain cycled at an initial high strain amplitude for a specified number of cycles followed by low strain amplitude cycling to failure. The resulting behavior termed 'Initially Overstrained Long Life Behaviour', can be analysed to estimate the durations of Stage 1 and Stage 11 crack growth periods. A preliminary study of surface damage associated with this overstrained long life behaviour is also included. (Author)

Low-cycle flexural fatigue tests were conducted on 1-inch-thick 5086-H116 and 5456-H117 aluminum alloy plates to provide engineering data for use in the hull design of high performance surface ships. The results indicate that fatigue life is similar for both alloys despite strength differences, slightly reduced by the presence of sea water; appreciably reduced due to welding; significantly improved by grinding, but only if the ground surfaces are free of porosity; and unaffected by either mechanical peening or a postweld remelt treatment. (Modified author abstract)

Cyclic inelastic deformation response and fatigue notch factor are presented and discussed for two metals of contrasting stress-strain behaviour (an aluminum alloy 2024-T351 and a mild steel SAE 1015). Thin circular or elliptical notched plates fabricated from these metals were subjected to cyclic straining in a servo-controlled testing machine. Results of these tests are discussed in terms of cyclic stress and strain concentration factors and related to notch plate deformation through a parameter derived fron Neuber's rule. The results indicate that the deformation analysis employed, rather than a material 'size effect' is responsible for values of K sub f less that K sub t. (Author)

As the stress changes in an aircraft (or any other) structure, changes also occur in the material of the structure. Some stress changes or cycles are large enough to cause some amount of fatigue damage, even though this damage is not ordinarily discernible. There are three main problem areas in designing aircraft structures so that the accumulation of fatigue damage does not threaten safety--evaluation of cumulative damage; predicting and describing the fatigue-producing stress variations that will be experienced; and accounting for the wide scatter in fatigue life that is observed for seemingly identical test specimens and structures. The first, cumulative damage, arises because stress cycles in aircraft structures vary so greatly in size, number, and order that it is a practical impossibility to make enough tests to cover all variations. Therefore, fatigue damage caused by the many different stress cycles must be evaluated by adding up the effects of individual cycles. If we understood well enough the physical processes going on in a material during each stress cycle, this addition, or determination of cumulative effects, would be no problem. Lacking this understanding, evaluation of cumulative damage rests on theoretical methods, related in varying degree to the physical process of fatigue and to experiment. This Memorandum presents an investigation of the basic concepts of cumulative damage and of several current cumulative-fatigue-damage theories.

The report evaluates the effects of strength level, Charpy V-notch energy, prestraining, prestraining and stress relieving, and austenitizing temperature on the fatigue life of a fully quenched HY-80 steel composition. The fatigue data developed indicate that the designer would have to be cautious when going to higher strength steel when using a safety factor which is considered satisfactory for lower strength steels, i.e., if higher strength steels are to be used, larger safety factors are necessary to obtain a comparable fatigue life. The limited data presented on experimental HY-150 steels indicate that caution will have to be exercised in evaluating large specimen fatigue data.

Axial-stress fatigue tests were conducted on 1 unnotched and 2 notched types of extruded Mg alloy ZK60A-T5 under various conditions of mean and alternating axial stresses. The results are presented as stress-number-of-cycles (S-N) curves. The S-N curves for unnotched specimens were flat with an abrupt knee at 10 to the 5th power C; beyond this, the curves were almost horizontal, indicating a definite endurance level, although the effect was not so marked for mild-notched and sharp-notched specimens. The fatigue life of the Mg alloys was more sensitive to alternative than to means stress, particularly for notched specimens whose curves for 10 to the 5th power and 10 to the 7th power c were flat. The fatigue strength-reduction factor varied with the stress ratio and stress magnitude., Report on Fatigue Properties of Structural Materials.

Partial Contents: A Simplified Nonlinear Method for Estimating the Fatigue Life of Acoustically Excited Panels, Studies on the Dynamic Impact of Jet Engine Blades; Natural Frequencies and Damping of Full-Scale Hydrofoils by 'Pluck Test' Methods, Ground Tests of an Active Vibration Isolation System for a Full-Scale Helicopter, Shock Mitigation System Subjected to Thirteen Feet of Ground Motion - Cannikin Event, Viscoelastic Epoxy Shear Damping Characteristics, and Influence of an Absorber on Machine Tool Vibration., Presented at the Symposium on Shock and Vibration (43rd) Held at Pacific Grove, CA on 5-7 Dec 1972. See also Part 1, ADA112527 and Supplement 1, AD923949, Supplement 2, AD532167 and Supplement 3, AD532171.

The application of cathodic protection extends the fatigue life of HY-80 in salt water, and this would be expected to be the more marked the lower the cycle rate. The intrusion of a hydrogen embrittlement phenomenon, however, precludes retention of air fatigue life in salt water by cathodic protection if the cycle rate is slow.

Specimens were tested in a vibrating beam machine at 1800 cycles per minute dynamic load, and measured by electrical strain gage bridge and static tension tests in testing machine. S-N curves at range ratio of 0.2 were obtained for each value of rivet pitch as used in single row lap joint. Families of constant rivet pitch curves were developed, which define fatigue life for specimens. Curves showing variation of effective stress concentration factor in fatigue with rivet pitch and maximum load per rivet are established.

Results of an analysis to determine the effect of overload operations on wing fatigue life are presented. The investigation was confined to one transport-type airplane, which was assumed to operate at cruising power and with overload up to 50 percent of design gross weight. Overload weight concentrated in the fuselage was found to adversely affect the fatigue life, but overload weight distributed proportionally to the design gross weight had negligible effect on the fatigue life. The fatigue life, furthermore, was adversely affected by overload to a smaller degree than the single-gust life. As in the case of single-gust life, the wing-weight ratio was a main factor in determining the relative reduction of fatigue life by overload.

Observations have been made on the microstructure of metals subjected to fatigue stresses. The changes observed include the appearance of deformation bands and crystallites in the original grains. A modification of the fatigue process occurs at high stresses where the rapid formation of crystallites causes a widespread disturbance of the grains.

The fatigue of 10 per cent cold worked and aged (1500 F) Eaynes Stellite Co., R-235 nickel base alloy spot weld lap and fusion weld butt Joints was determined at room temperature and 1500 F with a 4/9 test u1timate strength maximum fatigue load. Spot welds were tested in thickness combinations of 0.020" to 0.020", 0.020" to 0.040" and 0.040" to 0.063", and fusion weld thickness combinations were 0.016" to 0.016", 0.040" to 0.040" and 0.063" to 0.063". Fatigue life data are given.

The Dynamic Test Method was successfully applied for obtaining core fatigue in shear by reversed bending of a double cantilever beam sandwich specimen containing heavy tip-end masses. The testing approach consists of applying forced vibrations at resonant frequency with an electromagnetic shaker for each stress level desired. Reliable and reproducible S-N fatigue curves were produced on adhesive-bonded aluminum alloy and brazed stainless steel specimens containing representative shear test areas. The uniformity of the core cell geometry and quality of the interface bond were found to have a significant effect on the fatigue life of the sandwich construction. Problems associated with specimen support, shear and bending stresses, symmetrical balancing, stress concentrations, and transmissibility response were overcome through refinement of specimen configuration and test procedure.

The effect of hardness, surface finish and grain size upon the compressive rolling contact fatigue strength of M-50 bearing steel has been studied. Considerable testing on the RC Rig and statistical treatment methods have been included. A mathematical expression relating these variables to life expectancy is presented and the optimization of these variables is discussed. It is shown that bearing fatigue of M50 increases by increasing hardness, decreasing surface, and increasing grain size. The optimum life identified occurs at Rc 64 hardness, 1.5 RMS surface finish, and a grain size of ASTM 2

Though fiber ropes belong to the oldest man made products, little is known about their mechanical behaviour and about factors influencing this. Rope manufacturing and the use of rope in various fields is heavily based on accumulated experience, which was inherited and improved during many centuries of rope use. However, its general use did not involve rigorous scientific and engineering analysis until fairly recently. With the introduction of synthetic fibers and new rope constructions within the last 30 years and numerous new applications of ropes in engineered systems, scientific methods are required more and more to describe and predict the mechanical behaviour of ropes in general and synthetic fiber ropes, in particular. This Handbook will give up to date information on the work which has been done to establish what may be called rope physics or rope mechanics. The goal is to turn fiber ropes into engineering tools with predictable mechanical response to applied forces and strains and to environmental conditions. The Handbook starts with an introduction into the basic characteristics of ropes, explaining them as mechanical models and as textile structures. The mechanical properties of rope such as strength, weight, breaking length, are explained next, giving special attention to the fact that fiber ropes stretch considerably under applied loads and thus absorb mechanical energy. Reaction of ropes to loading and stretching in use is covered next.

The object of the evaluation was to determine the fatigue life of a 1 1/4 inch diameter 6 x 19 IWRC wire rope when subjected to repeated cycles of operation over a 50 inch pitch diameter sheave while under a tensile load of 12,000 pounds. This wire rope was to be subjected to test until either 3 million cycles of operation had been completed, or until failure of the wire rope was noted. Failure was considered to occur when the first outer armor wire break was noted. It should be noted that current state of the art precludes the determination of inner armor wire breaks, while under use conditions.