bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Shock: A Contributing Factor to Laser Damage in Optical Thin Films Used for High Power Continuous Wave Laser Optics
Authors: Palmer JR 
Published: February 2009

The direction of this paper is to provide a theoretical model and supporting empirical data for evaluation of laser damage to optical thin films subjected to high power Continuous Wave laser irradiation. Basically, there has been a seeming anomaly in the maximum temperature that optical thin films can withstand before they fail to perform their function. On the one hand, a paper was presented to the Laser Boulder Damage Symposium that clearly provided empirical data that a number of oxide coating materials could reach 59°C to 680°C before failure set ia On the other hand, many investigators have found that coatings have failed at temperatures of 200°C to 300°C.
In this paper we set out to demonstrate that both conditions could be correct, rather than just one or the other. The equations for the absorption and subsequent temperature rise in the multilayer stacks are provided. The temperature rise of the substrate is evaluated and the equations for the actual thermal shock resulting from the conditions in the optical thin films, the substrate, and sensitivity of both to the materials that comprise the optical thin films and the substrates combination. Several coating chemistry combinations and three diverse substrate materials are evaluated and plotted based on measurements made and reported some years ago.
Reverse Thermal Wave Approximation for Temperature Transients in Optical Thin Films and Substrates — Reflective Optics for High Power Repetitive Pulsed Lasers
Authors: Palmer JR 
Published: February 2009

This is the companion paper to the Reverse Thermal Wave Approximations for High Power Continuous Wave Lasers. The purpose of this paper is to provide equations that will allow the optical designer to evaluate the temperature gradient in optical thin films and substrates under transient conditions. The semi-infinite plate models have been described rather extensively in other publications. However, the problem that is treated in this paper is that set of boundary conditions that do not satisfy the semi-infinite plate condition.
It is not uncommon to have coated reflective optics that have very thin substrates. For those conditions it is necessary to evaluate the temperature transient much differently than one would if the substrates were of sufficient thickness to satisfy the semi-infinite plate boundary. One finds that the temperature rise and gradients are substantially different for very thin substrate conditions. The Reverse Thermal Wave Modelwill provide the ability to evaluate the temperature gradients during the transient with closed form approximations.
The repetitive pulsed case has a substantially different characteristic temperature profile from that of the continuous wave and in this paper the equations and figures are provided to reflect the unique character of the temperature gradients in the optical thin films and substrates as a function of the hertz rate and pulse width. It becomes clear that the duel cycle of heating and cooling coupled with the thermal shock play important roles in the damage thresholds of many optical components in high power laser systems.
Effect of Elevated Temperatures on the Low Cycle Fatigue of 2.25Cr-1Mo Steel—Part I: Constant Amplitude Straining
Authors: Polák J , Helešic J , Klesnil M 
Published: February 2009

A 2.25Cr-1Mo steel was subjected to constant amplitude straining in the temperature interval 22 to 550°C. The conventional low-cycle fatigue properties at 22, 350, 450, and 550°C at constant diametral strain rate ˙ϵd = 5 × 10−3 s−1 were measured. The fatigue hardening-softening curves, cyclic stress-strain curves, and Manson-Coffin curves were obtained at each temperature. A detailed study of the cyclic stress-strain response was performed on a computer-controlled electrohydraulic machine. The temperature dependence of the cyclic yield stress was measured using a multiple step test procedure. The stress-dip procedure in cyclic straining was adopted in order to separate the effective and internal component of the cyclic stress. The dependence of both components on temperature and during fatigue life was measured.The effective stress component was found to be relatively high in this material and drops only mildly with temperature. The typical temperature dependence of the cyclic stress is due to the internal stress that drops quickly above 450°C and at 550°C is considerably lower than the effective stress. With continued cycling, the decrease of both components contributes to cyclic softening.Both the cyclic stress-strain response and fatigue life were affected by the strain rate and hold periods within the cycle. The time-dependent effects were studied in detail at 550°C. The frequency dependence of fatigue life at different strain amplitudes was measured. In addition to continuous straining, three basic types of hold times within the cycle with strain or stress relaxations were applied. The experimental data were analyzed, and a set of parameters to correlate the low-cycle fatigue life of the material with various straining conditions was evaluated.
Low Cycle Fatigue of Some Aluminum Alloys
Authors: Chung YS , Abel A 
Published: February 2009

Axial strain-controlled tests were performed on five aluminum alloys to provide information on their cyclic behavior. The alloys chosen for this investigation represent a complete survey of the strengthening mechanisms associated with commercial aluminum products. The strengthening microstructures ranged from subgrain and dislocation strengthening in the 1200 alloy, solid solution strengthening by magnesium in the 5083, and the high density of GP zones and finely dispersed precipitates in the case of the 7005, 6351, and 6061 alloys. The five alloys were plant-fabricated with commercial tempers.
One important aspect of the tests was the detailed measurement of the hysteresis loop shape change during cycling and its possible correlation with the fatigue performance. The fatigue results show the effect of microstructure and confirm the presence of a break in the Coffin-Manson plot.
Very Low Cycle Fatigue Life Influenced by Tensile or Compressive Prestrain
Authors: Iida K 
Published: February 2009

The effects of excessive prestrain in tension or in compression upon very low-cycle fatigue life were investigated for two mild steels and two high strength steels as an aid in the analysis of a ship failure in service, in which the bow structure was broken off due to local buckling and by low-cycle fatigue in extremely heavy sea conditions. The test series in the present investigation was: (1) uni-directional tension test after prestraining, (2) completely reversed strain cycling tests of non-prestrained material with several strain ranges, (3) tensile or compressive straining directly followed by completely reversed strain cycling, and (4) completely reversed strain cycling tests of specimens which were machined out of previously prestrained large diameter specimens.
The residual static fracture ductility decreases as a function of the amount of prestrain, showing much more loss of ductility in the case of compressive prestrain. Fairly good agreements on strain range and fatigue life were found between experimental data and estimated values calculated after Manson's and Iida's formulae. The failure life of a specimen subjected to prestrain showed a remarkable decrease from the failure life of the original material depending on three parameters: amount of prestrain, direction of prestrain, and specimen surface conditions. The worst case in the range of the present tests is that of tensile prestraining directly followed by strain cycling. In this case the low-cycle fatigue failure life of a prestrained specimen is, as an example, reduced by 93% of the failure life of the original material, when the amount of the tensile prestrain is 60% of the original static fracture ductility based on area reduction to failure.
Effects of Compression and Compressive Overloads on the Fatigue Behavior of a 2024-T351 Aluminum Alloy and a SAE 1045 Steel
Authors: DuQuesnay DL , Pompetzki MA , Topper TH , Yu MT 
Published: February 2009

Smooth cylindrical specimens of 2024-T351 aluminum alloy and SAE 1045 steel were tested under constant amplitude cycling to study the effect of compressive stress on fatigue life. The results show a reduction in the fatigue life at constant maximum stress as the compressive portion of the stress cycle is increased.
Tests performed to study the effect of a periodic compressive overload on the order of the yield strength show an increasing reduction in fatigue life at constant maximum stress as the frequency of application of the overloads is increased. The compressive overload cycle significantly increases the damage done by subsequent smaller cycles, including those far below the constant amplitude fatigue limit. The results indicate that the present techniques used for damage summation for variable amplitude service histories may give grossly unconservative fatigue life predictions, especially for histories containing large compressive load cycles accompanied by a relatively large number of small cycles. It is suggested that conservative life predictions for such histories can be made using the stress-life curve from constant amplitude tests with compression on the order of the yield stress accompanying every cycle.
A Model for Predicting Low Cycle Fatigue Life under Creep-Fatigue Interaction
Authors: Rie K-T , Schmidt R-M , Ilschner B , Nam SW 
Published: February 2009

An attempt is made to predict fatigue life under high-temperature low-cycle fatigue conditions with superimposed hold times. It is well recognized that a reduction in life in this region is caused by the nucleation and growth of cavities along grain boundaries. The cavities can be formed by vacancy clustering, dislocation pileup, and grain boundary sliding. The subsequent growth leads to grain boundary cracking and intergranular fracture.
The possibility of unstable crack advance is given if the crack tip opening displacement becomes equal to a critical cavity configuration. To describe this configuration we postulate a power function for cavity growth.
Experimental data and the predicted values show excellent agreement, indicating the important role of creep cavitation for creep-fatigue life prediction.
Influence of Temperature and Environment on the Fatigue Mechanisms of Single-Crystal and Polycrystal 316L
Authors: Driver JH , Gorlier C , Belrami C , Violan P , Amzallag C 
Published: February 2009

Single-crystal and polycrystal 316L specimens were fatigued at constant plastic strain amplitudes in the range 10−4 to 2 × 10−2 in air and in vacuum (about 3 × 10−4 to 10−3 Pa) at 20, 300, and 600°C. The temperature and strain dependencies of the single-crystal cyclic stress-strain response are qualitatively similar to those of the polycrystalline material.
In air, the fatigue lives of both polycrystals and single crystals decrease by about an order of magnitude at 600°C compared with the results at 20 and 300°C. The fatigue lives of polycrystal specimens were prolonged in vacuum (compared with air) by factors of ∼2 or 3 at room temperature, to ∼20 at elevated temperatures and low plastic strains. The crack initiation mechanism of polycrystals tends to become partially intergranular at 600°C, but this change is not thought to significantly affect fatigue life. The reduction in fatigue resistance in air of both single and polycrystals at 600°C is attributed to oxidation—enhanced Stage I crack initiation.
An Integrated Approach to Creep-Fatigue Life Prediction
Authors: Agatonovic P , Heidenreich R 
Published: February 2009

There has been special interest recently in developing new, reliable analytical design methods for components under higher temperature conditions. However, at present, the use of material properties is still limited to arrays of single characteristics which do not interact with each other. In this work, several creep fatigue experiments on smooth specimens of IN 800 H have been carried out at 830°C. In some tests, these have also been combined with inside hysteresis loops to investigate the different effects on deformation and damage behavior which originate in a creep and fatigue environment. As a result of these tests, it has been found that the material behavior under creep-fatigue conditions can be significantly changed compared to the material behavior under simple load conditions. Therefore there is a need for life analysis methods to be expanded to include possible variations in properties; for greater accuracy, the material properties must be treated as a complex interacting system of parameters. The examination has been extended to a typical component used under high-temperature conditions. The results of the numerical analysis show that the stress-strain history in the critical area of that component is not simply strain controlled, as it is in the typical laboratory creep-fatigue interaction life test containing a tensile or compressive dwell at constant peak strain level. At high temperatures, the conditions in the component are more severe, causing the life to be reduced compared with the typical laboratory test. In this paper, these conditions are successfully simulated with the help of a generalized Neuber law: σ · εp = constant. Based on this ratio, the engineering method for evaluating component geometry and loading conditions and their effects on material behavior can be established.
On the basis of the results of this study, it follows that a very large amount of information on material behavior and on its component dependence is needed when the material properties are time-dependent, as in the design of hot components. For that reason, the satisfactory solution to designing components for high-temperature conditions requires an integrated approach, with full consideration of different interaction effects from the various influences in the main areas of the material deformation and damage behavior, and of the component effects. The results of this study may apply to the standard methodology of life prediction in high-temperature areas, which shall be developed in the future.
Oxidation-Fatigue Interactions in a Single-Crystal Superalloy
Authors: Wright PK 
Published: February 2009

This research was conducted to identify, understand, and model the interactions of oxidation and low cycle fatigue (LCF) in a single crystal nickel-base superalloy, René N4. The LCF testing was conducted at 1093°C (2000°F) in three test environments: purified helium (&lt;1 ppm oxygen), laboratory air, and enriched oxygen (80% oxygen at 2 atm pressure). Two cycle frequencies, 20 and ½ cpm, were investigated.The fatigue life and behavior of René N4 at 1093°C was found to depend on both oxygen concentration and cyclic frequency. These parameters influenced the portions of fatigue life required for crack initiation and crack propagation to different extents, although both portions were decreased under conditions which were environmentally more severe. A relatively small oxygen pressure dependence of fatigue life was seen (Nfα PO2−0.23). The fatigue process in René N4 showed a mixed time and cycle dependency leading to reduced fatigue life for longer cycles. Crack initiation was distinctly more time dependent than crack propagation and varied from ½ to 1/10 or less of the total fatigue life over the conditions investigated.Crack initiation in René N4 occurred by fatigue assisted cracking and spalling of oxide products to produce a roughened and pitted surface. This process also accelerated the observed oxidation rate. With further cycling, these pits developed into oxide spikes and then into sharp fatigue cracks. A modification of an oxidation-fatigue model by Antolovich was satisfactory in describing this process. The crack propagation process was also influenced by oxidation. However, the precise mechanism could not be clearly defined.
Thermal-Mechanical Cyclic Stress-Strain Responses of Cast B-1900+Hf
Authors: Marchand N , L'Espérance G , Pelloux RM 
Published: February 2009

A study was undertaken to develop an understanding of the fatigue response of superalloy B-1900+Hf under combined thermal and mechanical strain cycling in air. Comparative evaluations were made with existing thermal-mechanical data of B-1900+Hf and with results of a comprehensive study of the fatigue behavior of the same alloy under isothermal conditions. The thermal-mechanical fatigue (TMF) response was investigated for constant amplitude, fully reversed, mechanically strained cycling of uniaxially loaded specimens in the temperature range from 400 to 925°C. Experiments were conducted both with maximum strain in-phase with maximum temperature and out-of-phase with maximum temperature.
The TMF cycling was observed to cause more cyclic hardening than in isothermal fatigue experiments at the maximum and minimum temperatures. In terms of mean stress or plastic strain range, out-of-phase cycling was shown to be more deleterious than in-phase or isothermal cycling. However, few differences were observed in terms of the stabilized stress ranges. The asymmetric cyclic hardening/softening behavior is explained in terms of coarsening of the γ′ and associated strain field. For TMF cycling, the high temperature flow stress depends on the density of the misfit dislocations, whereas the low temperature flow stress is controlled by the magnitude and sign of the applied stress. The TMF cracking modes are discussed. The results show that the fracture criterion under TMF cycling is stress based.
Thermal Fatigue Testing of Coated Monocrystalline Superalloys
Authors: Holmes JW , McClintock FA , O'Hara KS , Conners ME 
Published: February 2009

Induction heating of stepped-disk specimens to study thermal fatigue of coated superalloys is well suited for studying anisotropic alloys and is easily adaptable for corrosive or inert atmosphere testing. Details of the experimental apparatus and results of a thermoelastic finite element analysis to find the stress-strain history are given.
To illustrate the technique, the effect of cyclic thermal strains on the durability of an aluminide coating applied to a typical monocrystalline nickel-base superalloy was studied in air. Results show that both the compressive strain encountered on specimen heatup and the tensile strain encountered on cooldown critically affect the aluminide coating degradation. After 6000 cycles of heating from 520 to 1080°C in 5 s, followed by 30 s cooling, 80% coating penetration by scalloping was observed. A similar treatment with 6 s cooling resulted in alumina-filled “cracks” extending into the substrate.
Influence of Nitrogen Solutes and Precipitates on Low Cycle Fatigue of 316L Stainless Steels
Authors: S Degallaix , G Degallaix , J Foct 
Published: February 2009

Improvement of monotonic and cyclic mechanical properties of 316 steels by nitrogen is studied for different nitrogen contents between 0.03 and 0.25 wt% at 20 and 600°C. At 20°C, yield and ultimate tensile stress increase almost linearly with nitrogen content to the detriment of ductility. Low-cycle fatigue (LCF) life also increases linearly with nitrogen solutes until 0.12 wt% nitrogen where a saturation of this effect occurs. This improvement is attributed to a more homogeneous distribution and to a better reversibility of plastic strain.
The influence of aging treatment at 600°C is studied on tensile and LCF properties at 20 and 600°C. An LCF life decrease with aging is more noticeable when nitrogen content is high. Furthermore, the higher the strain range, the more marked is the decrease in life at room temperature; this tendency is inverted at 600°C.
At 20°C, stress evolution during the hardening-softening stage is virtually independent of aging time but strongly dependent on nitrogen content. For high strain ranges at 600°C and high nitrogen content, the stress increases continuously until rupture, due to significant intergranular precipitation and embrittlement.
Quantification of Slip Lines in Fatigue
Authors: WG Fricke 
Published: February 2009

Although fatigue, even low-cycle fatigue, can occur at stresses below the engineering yield strength of a material, plasticity is involved because slip lines may appear on the surface of a test material. These slip lines increase in number in the early stages of fatigue and are indeed the precursors of ultimate failure. In a cyclic stress test, the initial rapid increase in number of slip lines produces slip saturation, after which other phenomena such as crack initiation become predominant. New slip lines are added at a decreasing rate.
Quantitative measurements have been made of slip lines in fatigue specimens and compared with the number in a tensile test of the same material. In fatigue, the equation describing the rate of addition of new slip lines requires that the stress be described in terms of how much the test stress exceeded a quantity, characteristic of the material, which can be thought of as a “yield strength” in fatigue. This quantity corresponded closely to the measured endurance limit of the material.
A comparison is made with similar measurements in a tensile test.
Effect of Elevated Temperatures on the Low Cycle Fatigue of 2.25Cr-1Mo Steel—Part II: Variable Amplitude Straining
Authors: J Polák , A Vašek , M Klesnil 
Published: February 2009

A 2.25Cr-1Mo steel was subjected to variable amplitude block straining at test temperatures of 22, 350, 450, and 550°C. A loading block having 500 strain peaks with an exponential probability density distribution and a constant diametral strain rate was generated. The loading block was analyzed by the rain flow procedure, closed hysteresis loops were identified, and peaks forming a cycle with stress amplitude smaller than half of the fatigue limit were deleted. The strain block characterized by the maximum strain amplitude was applied to a set of cyclindrical specimens in a computer-controlled electrohydraulic testing system.
Stress amplitudes of all closed hysteresis loops versus the number of blocks (i.e., the variable amplitude cyclic hardening-softening curves) were plotted. Similar hardening-softening behavior as in constant amplitude straining was observed. A plot of stress amplitudes versus plastic strain amplitudes in a block at the half-life (i.e., the service stress-strain curve) was obtained. The parameters of the service stress-strain curves were evaluated in dependence on the maximum strain amplitude and on the temperature. They were compared with the basic cyclic stress-strain curves.
The fatigue life in variable amplitude block loading (i.e., the number of blocks to failure) was plotted versus maximum strain amplitude. The experimental results were compared with the predictions using a linear cumulative rule combined with a rain flow counting procedure and the Manson-Coffin fatigue life curve. The actual to predicted life ratio was 0.4. The observed discrepancy was discussed in terms of the mechanism of fatigue damage under spectrum loading.