Size effects and energy disposition in impact-specimen testing of ASTM A 533 grade B steel

A series of impact-type specimens, ranging in thickness from 0.1 to 12 in., have been tested. The effects of size on the impact energy per unit volume of the plastically deformed material of the specimens tested are investigated using the laws of similitude. Complementary to this, a model illustrating the disposition of energy between shear lip and flat fracture is proposed and satisfactorily verified by the test results. It is shown that significant size effects on impact energy exist at all temperatures and, in particular, a size effect of around five exists even at upper-shelf temperature for 12-in.-thick impact specimens when compared to the energy from thinner specimens, say a Charpy impact specimen. This is to say that, on the upper shelf, the impact energy of a 12-in.-thick specimen is equivalent to between 25 and 30 ft-lb Charpy impact energy. To lend further support to the behavior thus defined, it is shown that the nil-ductility type behavior in 12-in. thicknesses is exhibited at around 145° F as compared to the similar behavior exhibited by regular drop-weight specimens at around 0° F. That is, the nil-ductility temperature, if redefined as a type of behavior and not confined to a given size specimen for 12-in.-thick plate, is about 145° F.     

Development of high-temperature biaxial-strain transducer for use to 1033°K (1400°F)

This study involved the development and evaluation of a high-temperature biaxial-strain transducer for measurement of strains up to 5 percent at temperatures approaching 1033°K (1400°F). The design requirements for transducer were established by specifications prepared by the Pressure Vessel Research Committee (PVRC) of the Welding Research Council. These specifications reflect the needs of the national laboratories and private industry as they relate to safety and structural-behavior studies of nuclear and advanced fossil-fuel systems, including piping, piping components, heat exchangers, and other pressure equipment. It was concluded, on the basis of the results from this study, that the transducer should perform satisfactorily at temperatures to at least 866°K (1100°F), and perhaps to 1033°K (1400°F). This paper should be of particular interest to those involved in high-temperature strain measurements or structural-behavior studies of energy systems (nuclear and fossil fuel) and components (piping, pumps, valves, heat exchangers, reactor components, etc).     

The application of strip strain gages for measuring residual surface stresses in beryllium

Evaluation and application of tiny, 0.031-in. gage length, constantan foil-strip strain gages for measuring residual surface stresses in beryllium parts are discussed. The strain gages were applied to one side of the beryllium parts at locations known to have high residual surface stresses. Small coupons were machined from the parts and the opposite side of the coupon was chemically milled with a 10 to 20-percent hydrochloric-acid solution. The strain-gage installation was protected with micro-crystalline wax. The etching process required approximately 20 hr at 75°F. Because of their high stability, glass-fiber-reinforced epoxyphenolic strain gages were used rather than the more readily available polyimide-backed strain gages. Details of the strain-gage installation are presented.     

Finite-element solutions for thermal stresses in steel-concrete composite bridges

The objective was to determine experimentally and analytically steady-state temperature distributions produced in the cross-sectional planes of steel-concrete composite simple-span bridges. The upper and lower surfaces were exposed to different temperatures. The research included the development of finite-element solutions for steady-state temperature distributions from known boundary conditions and the calculation of strains and stresses. Temperature and stress distributions were generally nonlinear with linear strains through the finite elements. Temperatures were predicted to ±1° F (±0.6° C). The experimental strains are linear through the composite section, with the computed finite-element strains generally giving slightly higher stresses. The concrete-slab stresses were overestimated for positive curvature and slightly underestimated for negative curvature. Concrete-slab stresses were relatively small when compared to their permissible stress. Temperature stresses in the steel beam were shown to be significantly large to warrant consideration in the design of these bridges. Stresses were calculated for short-term steady-state temperatures. Transient field conditions producing greater thermal stresses are now under investigation.     

Experimental analysis of perforated torispherical shells under external pressure

Load tests were conducted on torispherical shells at room temperature for the purpose of predicting mechanical behavior of a reactor-vessel head at 1200°F. These shells were models of a calandria-vessel head designed for use in the sodium-reactor experiment. Principles of dimensional analysis were used in designing the tests and relating experimental results to behavior of the full-scale structure. External pressure and point loads were imposed to simulate service conditions caused by submersion of the calandria in sodium and transient thermal contraction of process tubes. Deflections and strains were monitored at several locations throughout various loading sequences. The stability limit of one 36-in. diam shell was reached at a strain number of:

$$\frac{{p(external{\text{ }}pressure)}}{{E(modulus{\text{ }}of{\text{ }}elasticity)}} = 3.07 \times 10^{ - 6} $$     

A modified hole-drilling technique for determining residual stresses in thin plates

This paper presents a modified hole-drilling technique for measuring residual stresses in sheet and thin-plate materials. The primary advantage of the modification is that it eliminates the necessity for calibration of each experimental hole-gage assembly. The relaxation coefficients are calculated from theory, and the strain components which are extraneous to the true relaxation strains are determined and separated from the measured relaxation strains. Experiments were conducted on 0.050-in. (1.27-mm) and 0.125-in. (3.175-mm)-thickness aluminum-alloy specimens. Sources of extraneous strain components are analyzed and values for these strain components resulting from machining residual stresses and localized plastic yielding are determined. Finally, the recommended range of the nondimensional ratio of hole diameter to distance between hole center and strain-gage center is determined by the maximum permissible error in residual-stress estimates. The modified technique appears to be accurate within ±5 percent or better and is, therefore, comparable in precision with the X-ray technique.     

Balanced Biaxial Testing of Advanced High Strength Steels in Warm Conditions

The main purpose of the present work is to measure the stress–strain behavior under warm conditions (about 100 °C) of advanced high strength steel (AHSS) sheets up to large strains compared to uniaxial tension. The test equipment consists of two main parts, i.e., a hydraulic bulge tester and a heating device. A mechanical system is attached to the test equipment for measuring the membrane stress and thickness strain at the bulge pole. The stress–strain curves were measured for three kinds of AHSS sheets with the proposed test method for various initial temperatures (10, 50 and 100 °C). The proposed method does not provide isothermal stress–strain curves because the specimen temperature increases during the test due to the effect of deformation-induced heating. A numerical scheme using thermo-mechanical finite element (FE) simulations is suggested to deconvolute the isothermal stress–strain curves.     

Strain-gage installations for adverse environments

Seven projects in which resistance-type bonded strain gages were used in adverse environments are described. The projects involved: (1) force measurements in a 10^?10 torr vacuum, (2) load measurements over a temperature range of 75 to 300° F, (3) displacement measurements in a nonconductive fluid at 500° F, (4) dynamic displacement measurements in an electric field, (5) strain measurements in air at 600° F, (6) dynamic displacement and strain measurements to ?320°F, and (7) strain measurements in water at pressures up to 2500 psi and temperatures up to 300° F. This report provides detailed information about the gage installations, the transducers used and the performance obtained.     

Analysis of biaxial-fatigue damage at elevated temperatures

Two-level cumulative-damage fatigue tests were conducted on tubular 304 stainless-steel specimen under biaxial-strain conditions at elevated temperatures. Effects of temperature, biaxiality and sequence of straining were investigated. The experimental results are forwarted with a new approach that utilizes the Miner cumulative-damage rule. This approach has shown that fatigue damage at elevated temperatures of 538°C (1000°F) and 649°C (1200°F) accelerates and decelerates as a result of time of exposure to a given loading sequence. The effect of biaxiality is shown through the behavior of the material under axial and shear-strain components. The axial (tensile) strain component has shown to be the severest detrimental damaging component when compared to a shear-strain component. A damage mechanism emerges from the interaction of temperature and loading sequence. Its significance can be observed only when a certain life ratio has been exhausted.     

Residual stresses in evaporated AI-Si films

Residual stresses in vacuum evaporated thin Al-Si films were evaluated by measuring the deflection of a thin cantilevered substrate during removal of the film. Post-thermal treatment and thermal cyclings at temperatures between ?269° C and 560° C were also introduced to determine their effects on the residual stresses of the films.     

Evaluation of high-temperature strain gages for enrico fermi reactor vessel

Thermally induced strains in the Fermi reactor vessel will be measured with weldable strain gages during tests prior to criticality. Laboratory tests of these gages show that mechanical strains can be measured under static conditions at 900°F. Laboratory tests further show that the temperature coefficient of these gages becomes very small after about 170 hr of heating at 900°F, making it possible to measure strains resulting from temperature changes.     

Testing the space-shuttle thermal-protection coating

A light-weight insulation material and its protective glassy coating will protect thespace shuttle from temperatures as high as 1250°C (2300°F). The critical performance characteristics of the brittle coating are investigated using testing techniques developed to accommodate these extreme environments and the delicate material. These include an ultimate-strain test-specimen geometry which circumvents problems created by flawed edges, as well as a tension specimen preparation and loading system with which premature failures due to excessive bending moment are avoided. Additionally, an elevated-temperature mechanical strain transducer—useable at more than 870°C (1600°F)—is described. Potential alterations to this sensor are discussed which would make it functional at up to 1600°C (3000°F).     

A technique for cyclic-plastic notch-strain measurement

The interferometric strain/displacement gage was used to measure local strains of approximately ± 1 percent strain near a central notch in specimens undergoing completely reversed loading. Two notch geometries were tested: a circular hole and a keyhole slot with theoretical stress-concentration factors of 3.1 and 5.9 respectively. Measurements were made at both room and elevated temperatures (149° and 260°C) on three materials having different cyclic properties. This paper describes the experimental techniques for making the notch-strain measurements. The results of this series of tests are used in evaluating Neuber's cyclic rule.     

Photoelastic-coating analysis in thermal fields

If photoelastic-coating materials exhibited thermal conductivity and thermal expansion equal to that of structural materials, and if strain-optical sensitivity did not vary with temperature, photoelasticcoating analyses could be conducted in thermal fields exactly as in room-temperature test. Methods for circumventing problems associated with these material properties are presented. Corrections are introduced as analytically and empirically derived factors to account for birefringence resulting from differential thermal expansion of coating and workpiece. Surface strains induced by external loading and by thermal stresses can be performed in the temperature range of ?60° F to +350° F for tests of extended duration and to +500° F for brief periods.     

Evaluation of high-elongation foil strain gages for measuring cyclic plastic strains

The behavior of a certain type of high-elongation foil strain gages (l/32-in. gage length) was checked against the indications of a clip-on extensometer under conditions of cyclic plastic strain (strain range 0.5 percent to 2.8 percent). The gages exhibited limited capability of measuring cyclic plastic strains. Transverse and axial strain measurements by means of the gages enabled determination of Poisson's ratio for elastic and plastic conditions. Results are tabulated and discussed.     

A unique elevated-temperature tension-torsion fatigue test rig

A unique tension-torsion fatigue test set up is described that allows strain-controlled tests at temperatures exceeding 649°C. The machine uses a large die set as a load frame resulting in lower cost and superior parallel positioning of the crossheads. Disposable weld-on grips were found to be cost effective for elevated-temperature testing. A new extensometer using commercially available capacitance probes was developed which can operate at the elevated temperature without cooling. Capacitance ring probes were utilized in an attempt to measure through-thickness strains. The characteristic behavior of the ring probes is discussed. Design modifications needed to make a successful measurement of through-thickness strains at elevated temperatures are presented.