Thomas P. Rich

Case histories involving fatigue and fracture mechanics

Ever since the early days of research in fracture, numerous books and journals have been available to document the advances in the basic understanding of fracture and fatigue mechanisms and theory. The E-24 Committee on Fracture Testing of ASTM sponsored a Symposium on Case Histories Involving Fatigue and Fracture Mechanics in Charleston, South Carolina, on the 21st and 22nd of March, 1985. This book compiles the papers presented in that conference. The case history format was chosen for the meeting and the detailed examples of how fracture and fatigue concepts and data were applied to actual engineering components and systems. Sufficient information was sought to specify the geometrical, material, loading, environmental, and crack characterizations required to perform each case history investigation. Major areas of applications are pressure vessels, power generation equipment, structures, aircraft, manufacturing equipment, and bio-medical devices.

Fracture diagrams for cracked stiffened panels

Abstract A general equation is derived for the prediction of structural failure of two-dimen-sional cracked components in which the geometrical features of the component affect the stress intensity factor of the crack. The general equation is used to construct a new fracture diagram for a uniformly stressed sheet containing a crack which is constrained by two stiffening elements fastened to the sheet. By the use of an example it is shown that the shape of the fracture diagram, and hence the fracture behavior of the panel, depends on the spacing of the stiffening elements, rivet locations and the relative stiffness of the cracked sheet and the stiffeners. It is shown that there are stiffened panel diagrams which indicate that failure can occur at fracture toughness levels significantly higher than would be apparent from an unstiffened panel of similar material.

The effect of hot isostatic pressing on crack initiation, fatigue, and mechanical properties of two cast aluminum alloys

This article presents the results of an experimental materials testing program on the effect of hot isostatic pressing (HIP) on the crack initiation, fatigue, and mechanical properties of two cast aluminum alloys: AMS 4220 and 4225. These alloys are often used in castings for high temperature applications. Standard tensile and instrumented Charpy impact tests were performed at room and elevated temperatures. The resulting data quantify improvements in ultimate tensile strength, ductility, and Charpy impact toughness from the HIP process while indicating little change in yield strength for both alloys. In addition standard fracture mechanics fatigue tests along with a set of unique fatigue crack initiation tests were performed on the alloys. Hot isostatic pressing was shown to produce a significant increase in cycles to crack initiation for AMS 4225, while no change was evident in traditional da/dN fatigue crack growth. The data permits comparisons of the two alloys both with and without the HIP process.

A survey of fracture mechanics applications in the united states

Abstract Results are presented in graphical form based upon data collected in a survey of fracture mechanics applications in the United States, which was conducted during the first half of 1975. The participants numbered 235 designers, engineers and scientists from industry, government and university. The survey considered the field of fracture mechanics in its broadest sense, including all areas of design which involve the various aspects of fracture in solids. The questionnaire used in the survey is given in an Appendix. Continuing input is sought to the established data base on fracture in design, and completed questionnaires should be sent to T. P. Rich.

Specimen and automated test method development for investigation of fatigue crack initiation

Abstract An economical and effective test specimen has been developed for use in fatigue crack initiation studies. A dynamic materials-testing system was similarly developed for this purpose, consisting of a servohydraulic dynamic testing unit, high-resolution photomacrographic equipment, and computer control systems. The specimen and system permit fully-automated fatigue crack initiation testing, and crack lengths of approximately 0.001 inches have been detected with the peak load amplitude applied to the specimen. This paper presents the development of the specimen, the design constraints imposed by the system and the required test results, and the prototype test program and subsequent specimen modifications. Final specimen dimensions, the correlation between notch root stress and applied load, and recommendations for specimen use are also provided.

On the statistical nature of fracture

This paper explores the statistical nature of the mechanisms of fracture in structural materials and the loads that initiate them. The result of employing either a weak link or bundle model in the application of statistics to problems of fracture is examined. Experimental data is presented for the fracture of metal chains and the fracture of sheet aluminum containing machined cut-outs and cracks. The scatter in fracture loads for the chains and fracture toughness for the sheet specimens is statistically analyzed utilizing four statistical distributions: normal, lognormal, extreme value, and two-parameter Weibull functions. Based upon this work there appears to be no general a priori justification to utilize either the weak link or the bundle model in the statistical assessment of the fracture of typical engineering structural components.

Stress intensity factors for cracks emanating from pressurized semi-circular cylindrical cavities

Abstract Mode I stress intensity factors are given for the case of a crack emanating from the base of a semi-circular cylindrical cavity on one surface of a finite block. The cavity is under a uniform pressure and the block is restrained by a normal pressure on the surface of the block opposite to the cracked cavity. The solution was obtained by the modified mapping collocation technique. In addition to the stress intensity factor results, a comprehensive collocation accuracy control method is presented which utilizes computer graphics to provide added insight into the nature of the complex stress functions that represent the stress field solution. The geometries and loadings given provide a range of data potentially useful in the tool and die industry with particular application for metal forming and swaging dies.