Method and apparatus for determination of material residual stress

A device for the determination of residual stress in a material sample consisting of a sensor coil, adjacent to the material sample, whose resistance varies according to the amount of stress within the material sample, a mechanical push-pull machine for imparting a gradually increasing compressional and tensional force on the material sample, and an impedance gain/phase analyzer and personal computer (PC) for sending an input signal to and receiving an input signal from the sensor coil is presented. The PC will measure and record the change in resistance of the sensor coil and the corresponding amount of strain of the sample. The PC will then determine, from the measurements of change of resistance and corresponding strain of the sample, the point at which the resistance of the sensor coil is at a minimum and the corresponding value and type of strain of the sample at that minimum resistance point, thereby, enabling a calculation of the residual stress in the sample

Design of a scanning laser radar for spaceborne applications, phase 3

Design of scanning laser radar for spaceborne application

Construction and testing of a Scanning Laser Radar (SLR), phase 2

The scanning laser radar overall system is described. Block diagrams and photographs of the hardware are included with the system description. Detailed descriptions of all the subsystems that make up the scanning laser radar system are included. Block diagrams, photographs, and detailed optical and electronic schematics are used to help describe such subsystem hardware as the laser, beam steerer, receiver optics and detector, control and processing electronics, visual data displays, and the equipment used on the target. Tests were performed on the scanning laser radar to determine its acquisition and tracking performance and to determine its range and angle accuracies while tracking a moving target. The tests and test results are described

Evaluation of Brazed Joints Using Failure Assessment Diagram

Fitness-for service approach was used to perform structural analysis of the brazed joints consisting of several base metal / filler metal combinations. Failure Assessment Diagrams (FADs) based on tensile and shear stress ratios were constructed and experimentally validated. It was shown that such FADs can provide a conservative estimate of safe combinations of stresses in the brazed joints. Based on this approach, Margins of Safety (MS) of the brazed joints subjected to multi-axial loading conditions can be evaluated.

Failure Assessment of Stainless Steel and Titanium Brazed Joints

Following successful application of Coulomb-Mohr and interaction equations for evaluation of safety margins in Albemet 162 brazed joints, two additional base metal/filler metal systems were investigated. Specimens consisting of stainless steel brazed with silver-base filler metal and titanium brazed with 1100 Al alloy were tested to failure under combined action of tensile, shear, bending and torsion loads. Finite Element Analysis (FEA), hand calculations and digital image comparison (DIC) techniques were used to estimate failure stresses and construct Failure Assessment Diagrams (FAD). This study confirms that interaction equation R(sub sigma) + R(sub tau) = 1, where R(sub sigma) and R(sub t u) are normal and shear stress ratios, can be used as conservative lower bound estimate of the failure criterion in stainless steel and titanium brazed joints

There and Back Again: Perceived Long-Term Effects of a High School Immersion Abroad Experience

This qualitative phenomenological case study examined the perceptions of young adults regarding the effects of an approximately month-long immersion abroad experience in Cuernavaca, Morelos, Mexico, in which they participated when they were adolescents. School staff from Mexico who worked with these students were interviewed to help identify and articulate the context in which the adolescents studied and lived while in Mexico. Former sojourner participants recalled their memories of their attitudes and experiences before, during, immediately after, and long after the trip. Additionally, former sojourner participants were invited to share five photographic images they considered emblematic of the trip; their narrations of those images contributed to the data. Evidence indicated that school staff constructed a context heavily emphasizing the social environment in which students studied and lived. Evidence also indicated that former sojourner participants believe the trip, in conjunction with other experiences, contributed to their seeking other international experiences, pursuing international careers or careers that required intercultural skills, and establishing significant intercultural relationships

Failure Assessment of Brazed Structures

Despite the great advances in analytical methods available to structural engineers, designers of brazed structures have great difficulties in addressing fundamental questions related to the loadcarrying capabilities of brazed assemblies. In this chapter we will review why such common engineering tools as Finite Element Analysis (FEA) as well as many well-established theories (Tresca, von Mises, Highest Principal Stress, etc) don't work well for the brazed joints. This chapter will show how the classic approach of using interaction equations and the less known Coulomb-Mohr failure criterion can be employed to estimate Margins of Safety (MS) in brazed joints

Plyometrics

Plyometrics are a form of exercises in which an isometric-type overload, using the myotatic (stretch) reflex, is produced by means of an eccentric (lengthening) contraction, with the muscle being fully stretched immediately preceding the concentric (shortening) contraction. How fast the muscle switches from an eccentric to a concentric contraction will determine the athlete\u27s power. The goal behind plyometric exercise is to train the nervous system to react with maximum speed to the lengthening of muscle and to develop the muscle\u27s ability to shorten rapidly with maximal force. Plyometrics are first found in the literature in 1966 containing the work done by Veroshanski, a Soviet jump coach. In 1975, Fred Wilt, a United States track and field coach, introduced plyometrics to the United States. The theory of plyometrics is quite sound; however, very little has been done in terms of research. It is the intent of this paper to provide the reader with the history and physiology of plyometrics, examples of plyometric exercises, how to set up a program, and also present a research proposal to demonstrate the effectiveness of plyometric training in increasing an athlete\u27s vertical jump

Fracture toughness of SiC/Al metal matrix composite

An experimental study was conducted to evaluate fracture toughness of SiC/Al metal matrix composite (MMC). The material was a 12.7 mm thick extrusion of 6061-T6 aluminum alloy with 40 v/o SiC particulates. Specimen configuration and test procedure conformed to ASTM E399 Standard for compact specimens. It was found that special procedures were necessary to obtain fatigue cracks of controlled lengths in the preparation of precracked specimens for the MMC material. Fatigue loading with both minimum and maximum loads in compression was used to start the precrack. The initial precracking would stop by self-arrest. Afterwards, the precrack could be safely extended to the desired length by additional cyclic tensile loading. Test results met practically all the E399 criteria for the calculation of plane strain fracture toughness of the material. A valid K sub IC value of the SiC/Al composite was established as K sub IC = 8.9 MPa square root of m. The threshold stress intensity under which crack would cease to grow in the material was estimated as delta K sub th = 2MPa square root of m for R = 0.09 using the fatigue precracking data. Fractographic examinations show that failure occurred by the micromechanism involved with plastic deformation although the specimens broke by brittle fracture. The effect of precracking by cyclic loading in compression on fracture toughness is included in the discussion