Showing papers in "ASTM special technical publications in 1991"
TL;DR: In this article, the applicability of the J-integral test procedure to test short crack specimens in the temperature region below the initiation of ductile tearing where J 1 c cannot be measured was investigated.
Abstract: This study investigates the applicability of the J-integral test procedure to test short crack specimens in the temperature region below the initiation of ductile tearing where J 1 c cannot be measured. The current J-integral test procedure is restricted to determining the initiation of ductile tearing and requires that no specimen demonstrates brittle cleavage fracture. The J 1 c test specimen is also limited to crack-depth to specimen-width ratios (a/W) between 0.50 and 0.75. In contrast, the crack tip opening displacement (CTOD) test procedure can be used for testing throughout the entire temperature-toughness transition region from brittle to fully ductile behavior. Also, extensive research is being conducted to extend the CTOD test procedure to the testing of short crack specimens (alW ratios of approximately 0.15). The CTOD and J-integral fracture parameters are compared both analytically and experimentally using square (cross-section) three-point bend specimens of A36 steel with a/W ratios of 0.50 (deep crack) and 0.15 (short crack). Three-dimensional elastic-plastic finite element analyses are conducted on both the deep crack and the short crack specimens. The measured J-integral and CTOD results are compared at various levels of linear-elastic and elastic-plastic behavior. Experimental testing is conducted throughout the lower shelf and lower transition regions where stable crack growth does not occur. Very good agreement exists between the analytical and experimental results for both the short crack and deep crack specimens. Results of this study show that both the J-integral and the CTOD fracture parameters work well for testing in the lower shelf and lower transition regions where stable crack growth does not occur. A linear relationship is shown to exist between J-integral and CTOD throughout these regions for both the short and the deep crack specimens. These observations support the consideration to extend the J-integral test procedure into the temperature region of brittle fracture rather than limiting it to J 1 c at the initiation of ductile tearing. Also, analyzing short crack three-point bend specimen (a/W < 0.15) records using the load versus load-line displacement (LLD) record has great potential as an experimental technique. The problems of accurately measuring the CMOD of short crack specimens in the laboratory without affecting the crack tip behavior may be eliminated using the J-integral test procedure.
427 citations
TL;DR: A low-energy ion beam is a well-suited probe for such investigations because of the strong interaction between the ions in the considered energy regime and the surface atoms as mentioned in this paper.
Abstract: Surface characterization by ion scattering spectroscopy means the determination of the atomic masses and their geometric arrangement on a solid surface. A low-energy ion beam is a well-suited probe for such investigations because of the strong interaction between the ions in the considered energy regime and the surface atoms. “Low-energy” here refers to a range from a few hundred electron volts up to several keV. There are some essential features of ion scattering spectroscopy (ISS) or low-energy ion scattering (LEIS) which define its usefulness as a surface analytical method.
31 citations
TL;DR: In this article, a functional form was proposed to fit this material deformation pattern, which was used along with the load versus displacement records to evaluate J-R curves for many materials.
Abstract: The method of normalization has been used to develop J-R curves for metallic materials based only on analysis of load and displacement pairs in a ductile fracture test record. This method eliminates the need for crack length monitoring equipment. It not only provides a method for more easily conducting and evaluating J-R curve tests; but it could be useful for tests conducted under special conditions such as under dynamic loading. in restructive facilities such as a hot cell, or even in a facility with limited instrumentation. The method uses a normalized deformation curve which has a functional relationship resembling a power law in the beginning and a straight line later. A functional form is proposed to fit this material deformation pattern. This form was used along with the load versus displacement records to evaluate J-R curves for many materials. The results showed that the new method was a more accurate and versatile one for the assessment of the J-R curve. Compared with previous application of this method, the accuracy is remarkably improved in the beginning stages of the J-R curve where a J 1 c point is determined. The J 1 c point was analyzed on more than 60 specimens and found to be consistent with methods used in the ASTM test standards.
19 citations
TL;DR: The direct-current electric potential (d-c EP) method is receiving increasing attention as an alternative to the unloading compliance method for monitoring crack initiation and growth during fracture toughness testing of ductile metals.
Abstract: The direct-current electric potential (d-c EP) method is receiving increasing attention as an alternative to the unloading compliance method for monitoring crack initiation and growth during fracture toughness testing of ductile metals. Advantages of the d-c EP method include uninterrupted tests, continuous monitoring of crack extension, ability to accurately measure relatively large amounts of crack growth, and ability to be used at high displacement rates in many materials. The principal shortcoming of the d-c EP method (as with most other methods) is the uncertainty in defining the point of crack initiation in some tests. This paper describes Battelle's experience in using the d-c EP method to monitor crack initiation and growth in compact (tension) specimens machined from various pipes used in cooling systems of nuclear reactors. Among the materials investigated are carbon steel pipes (base metal and weld metal) and extremely ductile austenitic stainless steel pipes (base metal and weld metal). Discussed in the paper are: (1) estimation of the crack-initiation point from d-c EP data, (2) ability of the d-c EP method to accurately predict large amounts of crack growth in highly ductile metals. (3) modification of the Johnson equation to improve the accuracy of the d-c EP method for large crack growth, and (4) use of the d-c EP method at high displacement rates.
13 citations
TL;DR: In this article, a randomized intervention study among Dutch downhill skiers of 18 years and older was conducted to find an effective method to convince skiers that they have to adjust their ski bindings adequately.
Abstract: This article presents the results of a randomized intervention study among Dutch downhill skiers of 18 years and older. The objective of the study was to find an effective method to convince skiers that they have to adjust their ski bindings adequately. Literature study revealed that adequate adjustment of bindings (that is, by an expert and by means of a test device) is the most important behavior that can be manipulated to decrease the occurrence of ski injuries. Three conditions were varied: when (the 'moment') information materials were sent to skiers (one week versus three weeks before departure on a ski vacation), the medium (cassette versus leaflet), and the approach (fear-arousing versus neutral information). In this way, eight experimental groups were composed. In addition, a control group was formed that did not receive any information. The effects of the three conditions on the following factors were measured: attention, comprehension, intention, and behavior. The cassette received a higher degree of attention than the leaflet, irrespective of time or degree of fear. The level of comprehension was higher in all experimental groups than in the control group. The information sent long before departure and with a high degree of fear produced the most effect on the level of comprehension.
12 citations
11 citations
TL;DR: In this paper, a step-by-step procedure is given describing η factor calibration for an arbitrary specimen geometry based on a series of blunt notched specimens, which can be used to determine the η factors for any new test specimen geometry which might be added to existing test standards.
Abstract: A method for experimentally determining the eta (η) factor based on separation constants has been recently proposed. This method has two important implications for elastic-plastic fracture toughness testing. First, the method can be used to determine the η factors for any new test specimen geometry which might be added to existing test standards. Such specimens as disk compact, arc bend, and arc tension are used in the K 1 c test standard. They can be added to the J based standards if the specimen calibrations are known, one being the η factor calibration. In this paper a step by step procedure is given describing η factor calibration for an arbitrary specimen geometry based on a series of blunt notched specimens. The procedure proposed in this paper was then applied to existing blunt notch data for the traditional test specimen geometries, the compact, and single edge notched bend specimens. The results of the study show different values for η from these in the existing standards both in magnitude and trend with a/W. In addition they show a slight material sensitivity. The consequences of having incorrect h factors in the test standards are explored in a sensitivity study. These results are used to evaluate the importance of having correct η factors and recommendations are made.
11 citations
TL;DR: The empirical basis for behavioral risk factors other than those mentioned above is still rather weak and thus a restrictive policy with respect to health education for downhill skiers would seem appropriate.
Abstract: A problem analysis dealing with the importance of behavioral risk factors for ski injuries is based on the results of a case-control study conducted among Dutch skiers. In this study, cases (N = 572) were a sample of those who filed insurance claims for medical costs incurred as the result of a ski injury that prevented them from skiing for more than one day. Controls (N = 576) were a sample of uninjured skiers who filed insurance claims for nonmedical reasons. Not taking ski lessons appeared to be a risk factor among beginners (odds ratio [OR] = 2.5; etiologic fraction [EF] = 12%). Failure of bindings to release is associated with a higher risk (OR = 3.2) for lower extremity injury, indicating that optimal binding adjustment can have a substantial preventive effect. Surprisingly, binding adjustment in the Netherlands more often involved the use of a test device compared to the ski resorts involved. In the latter case, the injury risk was higher (OR = 1.6; EF = 17%). From our data and the available literature, it can be concluded that alcohol consumption is probably not an important risk factor for ski injury. Several findings from our study seem to indicate that risk underestimation may be a risk factor for ski injury, but further study is necessary on this point. Taken together, the empirical basis for behavioral risk factors other than those mentioned above is still rather weak and thus a restrictive policy with respect to health education for downhill skiers would seem appropriate.
10 citations
10 citations
9 citations
TL;DR: In this paper, the effects of side grooves, ligament depths, and the relationship between critical initiation J and G values are examined for a series of rubber-toughened polymers to determine the generality of the method for polymeric materials.
Abstract: The multispecimen J-integral technique ASTM Test Method for J 1 c , a Measure of Fracture Toughness (E 813-87) has been applied to a series of rubber-toughened polymers to determine the generality of the method for polymeric materials. The experimental procedures produce results that are similar in form with those found in the metals and ceramics literature. However, many of the procedures involving data analysis require reexamination. In this study, the effects of side grooves, ligament depths, and the relationship between critical initiation J and G values are examined. The use of side-grooved specimens for J testing is a viable way of experimentally verifying plane strain conditions. The ASTM E 813-87 recommendation for the allowable range of ligament depths appears to be inappropriate for toughened polymers. However, the recommendation of W/B = 2 as an experimental starting point is sensible. Finally, the J 1 c to G c relationship was explored. In separate, nonstandard K tests involving large specimens, the initiation point, G c , was defined at 2.5% crack growth. J 1 c , as calculated by the ASTM E 813-87 construction, was as much as 50% lower than this G c value. However. when comparing critical J and G values for specific crack growths, good agreement between the two tests was obtained, provided the crack growth was small. Although the current J 1 c construction provides a conservative estimate of the G c value, it is an open question whether the J 1 c value is appropriate for polymer design.
TL;DR: Sato et al. as discussed by the authors used a gravimetric technique to distinguish between vapor-phase and liquid-phase combustion, and found that the phase of combustion was erratic and inconsistent with the Glassman criterion which indicates that aluminum should burn in the vapor phase.
Abstract: The current view is that metallic materials burn in either the liquid or vapor phase. Evidence for this has been offered experimentally by the visual behavior of the combustion process and theoretically by the criterion proposed by Glassman, which is based on the boiling points and combustion temperatures of metallic materials and their oxides. However, results reported by Sato, et al. with aluminum, and recent tests at the NASA White Sands Test Facility with titanium and aluminum, suggest that metallic materials may undergo transitions and burn in both phases. These results have important implications on how we view the overall combustion mechanism of metallic materials, and are important in the development of burn-resistant alloys. An apparatus that monitos the sample weight change during combustion was used to study the burning phase of metallic materials. Materials that burn in the liquid phase were expected to gain weight while the molten, burning droplets were attached to the samples, whereas metals that burn in the vapor phase were expected to lose weight. Experiments were conducted with titanium and aluminum in oxygen at pressures ringing from 0,07 to 0.55 MPa (10 to SO psia). The titanium sample burned quiescently and there was a consistent increase in the test sample weight during the growth of the burning droplet, indicating that it burns in the liquid phase. These data are consistent with the Glassman criterion. For aluminum, however, the sample alternated between quiescent and turbulent burning, and the sample weight sometimes increased, sometimes decreased, and sometimes remained constant. This indicate that the phase of combustion was erratic and inconsistent with the Glassman criterion, which indicates that aluminum should burn in the vapor phase. Visual techniques are not sufficient to distinguish between vapor-phase and liquid-phase combustion. The gravimetric technique used in this work provides an important additional means of making this distinction.
TL;DR: In this paper, three models have been applied to very rapid compression of oxygen in a dead-ended tube, leading to peak temperatures of 1400 K are predicted These temperatures are well in excess of the autoignition temperature (750 K) of teflon, a frequently used material for lining hoses employed in oxygen service.
Abstract: Three models have been applied to very rapid compression of oxygen in a dead-ended tube Pressures as high as 41 MPa (6000 psi) leading to peak temperatures of 1400 K are predicted These temperatures are well in excess of the autoignition temperature (750 K) of teflon, a frequently used material for lining hoses employed in oxygen service These findings are in accord with experiments that have resulted in ignition and combustion of the teflon, leading to the combustion of the stainless steel braiding and catastrophic failure The system analyzed was representative of a capped off-high-pressure oxygen line, which could be part of a larger system Pressurization of the larger system would lead to compression in the dead-end line, and possible ignition of the teflon liner The model consists of a large plenum containing oxygen at the desired pressure (500 to 6000 psi) The plenum is connected via a fast acting valve to a stainless steel tube 2 cm inside diameter Opening times are on the order of 15 ms Downstream of the valve is an orifice sized to increase filling times to around 100 ms The total length from the valve to the dead-end is 150 cm The distance from the valve to the orifice is 95 cm The models describe the fluid mechanics and thermodynamics of the flow, and do not include any combustion phenomena A purely thermodynamic model assumes filling to be complete upstream of the orifice before any gas passes through the orifice This simplification is reasonable based on experiment and computer modeling Results show that peak temperatures as high as 4800 K can result from recompression of the gas after expanding through the orifice An approximate transient model without an orifice was developed assuming an isentropic compression process An analytical solution was obtained Results indicated that fill times can be considerably shorter than valve opening times The third model was a finite difference, 1-D transient compressible flow model Results from the code show the recompression effect but predict much lower peak temperatures than the thermodynamic model
TL;DR: A cooperative test program to assess the oxygen compatibility of aluminum-lithium alloys with NASA White Sands Test Facility (WSTF), NASA Marshall Space Flight Center (MSFC), and the National Institute of Standards and Technology (NIST) led to the assessment of the mechanical impact test by NIST as mentioned in this paper.
Abstract: A cooperative test program to assess the oxygen compatibility of aluminum-lithium alloys with NASA White Sands Test Facility (WSTF), NASA Marshall Space Flight Center (MSFC), and the National Institute of Standards and Technology (NIST) led to the assessment of the mechanical impact test by NIST. There were substantially different variations in test parameters between the test laboratories; some of these led to significant variability in the actual energy absorbed by the specimens. Therefore, test results varied widely. To reduce the large disparities in interlaboratory test results, a number of changes are recommended in the current ASTM test standards.
TL;DR: In this paper, the fracture toughness of polyvinylidine difluoride, medium and high density polyethylene is characterized using the J-integral method, and the results are compared with the results obtained from the multiple specimen method, which is often used for polymers.
Abstract: The fracture toughness of several polymes is characterized using the J-integral method. The single specimen method has been applied, and the tests were conducted on three-point bend specimens of polyvinylidine difluoride,medium and high density polyethylene. The results are compared with the J-R curves obtained from the multiple specimen method, which is often used for polymers and has proved to be successful. This has enabled a good degree of confidence be attached to the single specimen method. For each type of polymer, the J-R curves obtained from both methods are in good agreement. Hysteresis loops are observed during unloading and reloading because of the viscoelastic nature of the polymers, and the shape of the loops was affected by the friction at the support rollers. The distinction of J 1 c values determined according to the ASTM Standards E 813-81 and E 813-87 is shown. The E 813-87 procedure predicts a more consistent J 1 c value than the E 813-81, but the adoption of the 0.2 mm offset blunting line does not reflect the actual initiation point and the advantages and drawbacks of each method are discussed. The blunting line suggested in the E 813 protocols is found to be inappropriate for describing the blunting mechanisms of polymers. Some tests were performed at different loading rates to determine the rate sensitivity of both the J 1 c values and J-R curves. It is suggested that the maximum allowable crack extension recommended for the J controlled growth condition is too conservative for polymers, and it is noted that the crack growth is difficult to measure accurately. A maximum allowable crack extension of 10% of the uncracked ligament is considered to be appropriate.
TL;DR: In this article, an experimental program was performed to determine the oxygen compatibility of selected metals under the high surface area-to-volume ratios and adiabatic conditions encountered in commercial use.
Abstract: High-surface-area metallic structured packings are finding increasing use in the cryogenic distillation of air An experimental program was performed to determine the oxygen compatibility of selected metals under the high-surface-area-to-volume ratios and adiabatic conditions encountered in commercial use Under some conditions brass packing unexpectedly had a higher relative flammability than aluminum, which is contrary to reported test results using metal rods and strips This is due, we believe, to the specific geometric and adiabatic configuration of the packing material which appears to enhance the propagation of combustion in brass Aluminum flammability in gaseous oxygen has been shown to be very dependent upon argon dilution and, in the presence of liquid oxygen, strong energy releases have been observed, similar to those experienced with aluminum powder and liquid oxygen Copper was found to be nonpropagating in all tested oxygen purities These findings suggest that results from oxygen compatibility tests on rods and strips cannot be used reliably for ranking the suitability of materials in high-surface-area-to-volume ratio and adiabatic configurations
TL;DR: In this article, the combustion of cylindrical rods 3.81- to 11.43-cm long, with diameters of 0.10, 0.20, and 0.32 cm, in normal gravity and microgravity was investigated.
Abstract: The combustion of iron at high oxygen pressure in normal gravity and microgravity was investigated. Cylindrical rods 3.81- to 11.43-cm long, with diameters of 0.10, 0.20, and 0.32 cm, were burned in 100% gaseous oxygen, in normal gravity and microgravity, and the results were compared and contrasted. Two types of tests were conducted: 1) gravitational gradient tests and 2) microgravity combustion tests. The gravitational gradient test results showed that burning iron rods do not extinguish with a reduction in the gravity level, and may, in view of an observed increase in the consumption rate of the rod, have combustion enhanced in microgravity environments. The microgravity tests showed that the same dependency exists between rod diameter, oxygen pressure, and regression of the melting interface in normal gravity as in the microgravity combustion of iron rods: as the oxygen pressure is decreased, or the rod diameter increased, the regression of the melting interface decreased. The dominant processes in the combustion of metal rods are circulation of the metal, oxygen, and combustion products in the molten ball, and heat transfer to the solid rod. This circulation in the molten ball is not controlled by buoyancy, but is believed to be produced primarily due to differences in surface tension.
TL;DR: Three flame types can result when an ignition source is applied to a tube of a combustible material through which an oxidizer flows if the oxygen concentration inside the tube is greater than the tube material's limitingoxygen index (LOI).
Abstract: Three flame types can result when an ignition source is applied to a tube of a combustible material through which an oxidizer flows If the oxygen concentration inside the tube is greater than the tube material's limitingoxygen index (LOI), an opposed flow flame can spread along the inner surface of the tube (primary intraluminal flame) This flame, which requires a forced flow, consumes the supplied oxygen (fully or in part) and produces combustible, toxic gases which emerge from the free end (and ignition hole where applicable) These gases can then react with the oxygen in the ambient environment and thereby support the second flame type (secondary jet diffusion flame) If the LOI is exceeded outside the tube, an extraluminal flame (the third flame type) can occur, and be supported by natural convection
TL;DR: In this article, the upward burn propagation behavior of wire meshes was studied and the results showed that wire meshes with 3.2-mm (0.125-in) diameter were the least flammable alloys.
Abstract: The upward burn propagation behavior of rolled wire meshes was studied. Samples made from carbon steel, Copper 100, Monel 400, Nickel 200, 304 stainless steel, and 316 stainless steel were tested in oxygen at up to 0.77 MPa (100 psig). The samples were mounted vertically and ignited at the bottom using an aluminum-palladium igniter wire. Nickel 200 did not burn at any pressure. Copper 100 and Monel 400 burned completely at 0.33 MPa (35 psig) and 0.085 MPa (0 psig) respectively. Monel 400 burned consistently at pressures ranging from 0.60 to 0.085 MPa (75 to 0 psig), but did not burn at 0.77 MPa (100 psig). 304 stainless steel, 316 stainless steel, and carbon steel burned completely at 0.085 MPa (0 psig). The consumption rates of the wire mesh samples increased as pressure increased. The rankings of the alloys based on the minimum oxygen pressure required to support self-sustained combustion and the average consumption rates for wire meshes and 3.2-mm (0.125-in.) diameter samples were compared. The overall ranking based on data obtained using the two test sample configurations, from the least to most flammable, was: Nickel 200, Copper 100, Monel 400, 304 and 316 stainless steels (same ranking), carbon steel.
TL;DR: In this paper, it was suggested that the J-integral at 2% crack growth may be a better parameter to characterize fracture than J at initiation, which corresponded well with values of K 1 c in the literature.
Abstract: Fracture tests have been conducted on polycarbonate in the elasto-plastic and fully plastic regimes. The fracture behavior was well characterized by the J-integral. The value of the J-integral at the initiation of crack growth, corresponding to J 1 c , was 2.1 kN/m (12.2 psi-in.) for the 1981 ASTM Test Method for J 1 c , a Measure of Fracture Toughness (E 813-81), and 3.3 kN/m (19 psi-in.) for the 1987 ASTM (E 813-87). It was found that the value of the J-integral at 2% crack growth, 4.4 kN/m (25 psi-in.), corresponded well with values of K 1 c in the literature. It is suggested that the value of J at 2% crack growth may be a better parameter to characterize fracture than J at initiation. The value of the J-integral at popin or unstable fracture, 7.3 kN/m (41 psi-in.), was consistent for all the experiments. No effect of crack length or thickness was observed for any of these values of J. Two difficulties with the use of the 1987 standard were found. The first was that the data did not coincide with the blunting line. More crack growth was measured than predicted by the blunting line. The second was that a valid data point between the 1 and 1.5-mm offset lines could not be experimentally obtained because of the nature of crack growth in polycarbonate.
TL;DR: In this paper, additional data was presented on the promoted ignition-combustion behavior of various Hastelloy® type materials, which are significant engineering alloys that may be encountered in or considered for gaseous oxygen applications in severe environments.
Abstract: Promoted ignition and more recently promoted combustion are terms which have been used to describe a situation where a substance with low oxygen compatibility ignites and supports the combustion of a more ignition resistant material. Previous papers by Union Carbide have reported on the investigation of this phenomenon as it related to carbon steel, 316L stainless steel, aluminum-bronze, Carpenter® 20 Cb-3, Incoloy® 65, Inconel® 625 and Haynes® 25. In this paper, additional data will be presented on the promoted ignition-combustion behavior of various Hastelloy® type materials, which are significant engineering alloys that may be encountered in or considered for gaseous oxygen applications in severe environments. In this investigation, alloys have been evaluated via both flowing and static (fixed volume) approaches using the rod configuration used in the joint ASTM-CGA-NASA program. Static tests have been conducted in a vessel of the same volume as the apparatus used by NASA in the joint ASTM-CGA-NASA test program conducted at WSTF and also in a larger 6.0 liter vessel. Oxygen-nitrogen gas mixtures with purities ranging from approximately 40% to 99.7% at pressures of 3.55 MPa to 34.6 MPa were used in the comparative studies of five Hastelloy® compositions. As an adjunct to this investigation, neural network techniques were utilized in the analysis of the data. Neural network analysis is an artificial intelligence technique which mimics the human brain. The data generated in this investigation and other work was incorporated into a predictive tool.
TL;DR: These devices exposed to CO 2, Nd:YAG, and KTP laser energy in various oxygen-nitrogen and oxygen-helium atmospheres showed that some tubes were ignition resistant under some conditions, and the Sheridan and Xomed tubes burned under most test conditions.
Abstract: The risk of an oxygen enriched airway fire during oropharyngeal surgery with a laser is supposedly minimized by the use of a laser-ignition-resistant endotracheal tube such as those made by Bivona, Mallinckrodt, Baxter Norton, Sheridan, or Xomed; or Merocel, a tube wrap marketed as laser resistant; or 3M copper, 3M aluminum, or Radio Shack sensing metallic tapes which are commonly used to protect standard tubes. We exposed these devices to CO 2 , Nd:YAG, and KTP laser energy in various oxygen-nitrogen and oxygen-helium atmospheres. Only the Baxter Norton tube and the 3M copper taped tubes did not burn under any test conditions. Other tubes were ignition resistant under some conditions, and the Sheridan and Xomed tubes burned under most test conditions.
TL;DR: In this article, the main test methods implemented at "L'AIR LIQUIDE - Centre de Technologie et d'Expertise" i.e., the bomb test, the gaseous oxygen pneumatic impact test (adiabatic compression test) and the liquid oxygen mechanical impact test will be presented first.
Abstract: In spite of their easier ignition capability compared to metals and ceramics, non-metallic materials are often used in oxygen atmospheres because of their specific properties and, consequently, miscellaneous methods have been developped to evaluate their ignition risks which depend on their service conditions. The main test methods implemented at "L'AIR LIQUIDE - Centre de Technologie et d'Expertise" i.e., the "bomb test" (determination of autogenous ignition temperature at high oxygen pressure), the gaseous oxygen pneumatic impact test (adiabatic compression test) and the liquid oxygen mechanical impact test will be presented first. Then, we will give our interpretation of the results which show that : . for use with high-pressure oxygen gas (up to 24 MPa), it is best to use materials with spontaneous ignition temperature at 12 MPa greater than or equal to 400°C ; however, this may not be a sufficient limit if extreme ignition sources can be expected ; on the other hand, it may not be possible to respect this limit if a compromise is required between the qualities of the product for which it is used and its resistance to ignition ; the following precautions must be taken in either of these cases : the equipment must be well-designed (small quantities of organic materials, protected wherever possible from the impact of the gas stream and in integral contact with their metal support), additional tests must be made on this equipment (such as adiabatic compression tests), a precise analysis of hazards must be made and types of use for which no incidents have been reported should be considered ; . for use with liquid oxygen, the materials must at least successfully pass the impact drop test at an energy level of 100 Joules.
TL;DR: In this article, an independent analysis using theoretical calculations with nominal test chamber configuration geometries was performed to evaluate the effects of small and large variations in test apparatus chamber configurations, test chamber test pressures, and in preset initial striker pin positions.
Abstract: An independent analysis using theoretical calculations with nominal test chamber configuration geometries was performed to evaluate the effects of small and large variations in test apparatus chamber configurations, test chamber test pressures [446KPa to 69.07 MPa], and in preset initial striker pin positions [striker pin transmits mechanical impact energy from the test apparatus drop plummet to material test samples within the test chamber]. The effects evaluated were the total energy losses between the drop plummet energy impartation to striker pin and the striker pin energy impartation to the test sample of different given test apparatuses. These total energy loss effects directly determine whether or not a sufficient percentage of the drop plummet energy is in fact transmitted to the test sample during mechanical impact tests.
TL;DR: In this paper, a modified pneumatic impact test was developed and evaluated which addressed the problems of the test currently used by NASA, and the test system modifications included a view-ported specimen chamber to view ignition, larger volume between the impact valve and the specimen, ability to adjust pressurization time and a modified specimen size.
Abstract: The gaseous oxygen pneumatic impact test has been used by NASA to evaluate the suitability of nonmetallic materials in high-pressure oxygen systems. Several studies have been conducted in the past few years to evaluate the repeatability and applicability of the test. These studies showed that the test has an unacceptable degree of variability. It was recommended that new methods be developed for evaluating the suitability of materials for use in high-pressure oxygen systems. A modified pneumatic impact test was developed and evaluated which addresses the problems of the test currently used by NASA. The test system modifications included a view-ported specimen chamber to view ignition, larger volume between the impact valve and the specimen, ability to adjust pressurization time, and a modified specimen size. Test procedure modifications included subjecting the specimen to a single impact (the current NASA test method required 5 impacts per specimen). The ignition properties appeared to be controlled by the autogenous ignition temperatures of the specimen materials. The modified test allowed the prediction of ignitions that have occurred in component tests and in field incidents that the method currently used by NASA would not have predicted. It is recommended that pneumatic impact ignition tests be performed on components in their use configuration, and that thermochemical methods be used for batch/lot qualification of materials.
TL;DR: In this paper, simple and non-incremental formulas for J D, J M, and crack extension, based on the single-specimen key-curve method using blunt U-notched specimens are proposed.
Abstract: A method to calculate the deformation theory J, J D , which takes into account the influence of crack growth on J, and a modified version of the J-integral, J M , to allow a large relaxation of restrictions on the amount ofcrack extension and specimen configuration were proposed by Ernst et al. In this work, simple and nonincremental formulas for J D , J M , and crack extension, based on the single-specimen key-curve method using blunt U-notched specimens are proposed. The methods are applied to the determination of J-R curve for three-point bend type and compact tension type specimens. The accuracy of the methods in the determination of the J-R curves is discussed, emphasizing the differences between J-R curves for J D and J M .
TL;DR: In this article, the authors used Weibull statistics, available energy analysis, and a constraint correction procedure to analyze the ductile-to-brittle transition region toughness data.
Abstract: Fracture toughness testing of steels in the ductile-to-brittle transition region is complicated by a high degree of data scatter. Variations in the amount of ductile tearing prior to cleavage initiation often accompany the data scatter. Dynamic toughness testing is shown to be experimentally successful at reducing the incidence of prior ductile tearing. For the displacement rates tested, dynamic toughness values are at or above the lower-bound static toughness. Analysis of transition region toughness data using Weibull statistics, available energy analysis, and a constraint correction procedure is discussed.