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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Investigation of the fracture mechanics of boride composites

Processing studies designed to produce boride composites with metal additives to lower fabrication temperatures and increase the impact strength are reported. Hot pressing experiments were performed with ZrB2 and Fe, Ti, and Zr employed singly as additives. Data for the characterization, impact tests, slow bend tests, and fracture strength are presented.

Kaufman, L. A.↗
NASA NTRS1972

A case study in technology utilization: Fracture mechanics

This review of NASA contributions to the technology of fracture mechanics illustrates a fundamental role of the Space Agency in a single technical area. While primarily pursuing its goal of minimizing the weight of flight hardware, NASA engineers have generated innovations having broad impact in nonaerospace communities. A review is given of how these specific NASA innovations are communicated to the technical community outside the Space Agency, and current application areas are outlined.

Source record↗
NASA NTRS1972

Correlation of stress-wave-emission characteristics with fracture aluminum alloys

A study to correlate stress wave emission characteristics with fracture in welded and unwelded aluminum alloys tested at room and cryogenic temperature is reported. The stress wave emission characteristics investigated were those which serve to presage crack instability; viz., a marked increase in:(1) signal amplitude; (2) signal repetition rate; and (3) the slope of cumulative count plotted versus load. The alloys were 7075-T73, 2219-T87 and 2014-T651, welded with MIG and TIG using 2319 and 4043 filler wire. The testing was done with both unnotched and part-through-crack (PTC) tension specimens and with 18-in.-dia subscale pressure vessels. In the latter testing, a real time, acoustic emission, triangulation system was used to locate the source of each stress wave emission. With such a system, multiple emissions from a given location were correlated with defects found by conventional nondestructive inspection.

Hartbower, C. E.↗
NASA NTRS1972

Determination of design allowable properties. Fracture of 2219-T87 aluminum alloy

A literature survey was conducted to provide a comprehensive report of available valid data on tensile properties, fracture toughness, fatigue crack propagation, and sustained load behavior of 2219-T87 aluminum alloy base metal and weldments, as applicable to manned spacecraft tankage. Most of the data found were from tests conducted at room temperature, -320 F and -423 F. Data are presented in graphical and tabular form, and areas in which data are lacking are established.

Engstrom, W. L.↗
NASA NTRS1972

Experimental investigation of fracture in an advanced fiber composite.

Pilot tests were run to determine the applicability of the concepts of linear elastic fracture mechanics (LEFM) to the description of the mechanical behavior of initially cracked specimens of advanced fiber composite laminates. It was found that the failure mechanisms in such specimens were largely crack-dominated and that LEFM procedures were applicable even when the apparent failure mechanism was not explicitly dominated by a starter crack.

Konish, H. J., Jr.↗
NASA NTRS1974

Probability of stress-corrosion fracture under random loading

Mathematical formulation is based on cumulative-damage hypothesis and experimentally-determined stress-corrosion characteristics. Under both stationary random loadings, mean value and variance of cumulative damage are obtained. Probability of stress-corrosion fracture is then evaluated, using principle of maximum entropy.

Yang, J. N.↗
NASA NTRS1972

Major crustal fractures in the Baltic Shield

The author has identified the following significant results. Initial analysis of the bands for images 1039-09322, 1039-09315, and 1040-09371 provide a detailed picture of a zone extending 500 km north-northeast from the northern coast of the Gulf of Bothnia. Highways (on bands 0.5-0.6 and 0.6-0.7), rivers (bands 0.7-0.8, 0.8-1.1) and bare fell tops are visible. Schist belts, as known from ground surveys, can be discerned from areas occupied by their basement rocks or major plutons. A number of sharp lineaments, apparently faults, are visible. Some major fracture zones, up to 50 km wide, that form distinct lineaments in weather satellite pictures and belong to the main objects of this study, are rather indistinct in the images but can be traced.

Tuominen, H. V.↗
NASA NTRS1972

Investigation of the plastic fracture of high strength steels

An investigation of the plastic fracture process to improve tensile strength in high strength steels is presented. Two generic types of steels are considered: a quenched and tempered grade and a maraging grade, in order to compare two different matrix microstructures. Each type of steel was studied in commercial grade purity and in special melted high purity form, low in residual and impurity elements. The specific alloys dealt with include AISI 4340 and 18 Ni, 200 grade maraging steel, both heat treated to the same yield strength level of approximately 200 ksi.

Cox, T. B.↗
NASA NTRS1973

Mineral exploration and fracture trends in Utah and Nevada, by ERTS-1 imagery

The author has identified the following significant results. Major structural trends have been compiled on five separate maps, at a scale of 1:1,000,000, of Utah and Nevada from ERTS-1 imagery. An arbitrary length of ten kilometers has been chosen as a minimum length of the trends. The selection is based upon: (1) obvious displacement of structures; (2) continuity or persistence of trends across structures; (3) line-up of outcrop patterns, drainage, erosional features or vegetation; and (4) near-linear trends. Several recognizable trend directions have noted, viz., N 10-15 deg W, N 35 deg W, N 80 deg W, N 30 deg E, and E-W. More than 1500 structural trends have been identified, some of which are mineralized and extend into pediment or shallow alluvial cover. Those fracture trends that exhibit mineralization in exposed bedrock will be assayed for mercury content with a soil-gas analyzer and similar collection will be done over alluvial posture blankets by the same technique with the hope of discovering blind mineralized zones that are not exposed on the surface.

Jensen, M. L.↗
NASA NTRS1973

Study of application of ERTS-A imagery to fracture-related mine safety hazards in the coal mining industry

The author has identified the following significant results. The Kings Station Mine in Gibson County, Indiana has experienced considerable roof fall problems. Detailed fracture mapping of the mine area was done with ERTS-1 and aircraft imagery, and a prediction map of roof problem areas was produced in advance of a visit. The visit to the mine and discussions with the operator indicated that of four zones mapped as potential problem areas, three coincided with areas of excessive roof fall. This positive correlation of 75% lends confidence to the validity of the technique being applied in the investigation. The mine officials expressed an interest in the project and are anxious to see the final product maps which are forthcoming.

Wier, C. E.↗