Mechanical testing definitions

The word lest is quite broad in its definition, and many of the inspection steps in the course of the compressor manufacturing cycle can appropriately be called tests. An example would be the material tests. The API mechanical equipment standards, however, attempt to narrow the test definition. This chapter will discuss testing within these narrowed definitions. The first test defined in most API mechanical equipment standards is the hydrostatic test, and it will, therefore, be the first test covered in the chapter. 

Mechanical Properties. The mechanical properties used for design shall be the minimum values allowed by the applicable material specification or shall be the minimum values determined by the manufacturer in accordance with the test procedures specified in ASTM A370 Methods and Definitions for Mechanical Testing of Steel Products, or by mill certification for mill products. The yield point shall be used in lieu of yield strength for those materials exhibiting a yield point. Yield strength shall be determined at 0.2% offset. 

GENERAL NOTE Titles of referenced standards not listed in the Specifications Index for Mandatory Appendix IX are as follows A 20, General Requirements for Steel Plates for Pressure Vessels, and A 370, Test Methods and Definitions for Mechanical Testing of Steel Products. 

ASTM E 6-88, Standard Definitions of Terms Relating to Methods of Mechanical Testing, Aimual Book of ASTM Standards (1989), Vol. 8.03, p. 672. 

Determination of the residual antioxidant content in polymers by HPLC and MAE is one way to determine the amoimt needed for reasonable stabilization of a material, and also to compare different antioxidants and their individual efficiencies. During ageing and oxidation of PE, carboxyhc acids, dicarboxylic acids, alcohols, ketones, aldehydes, n-alkanes and 1-alkenes are formed [86-89]. The carboxyhc acids are formed as a result of various reactions of alkoxy or peroxy radicals [90]. The oxidation of polyolefins is generally monitored by various analytical techniques. GC-MS analysis in combination with a selective extraction method is used to determine degradation products in plastics. ETIR enables the increase in carbonyls on a polymer chain, from carboxylic acids, dicarboxyhc acids, aldehydes, and ketones, to be monitored. It is regarded as one of the most definite spectroscopic methods for the quantification and identification of oxidation in materials, and it is used to quantify the oxidation of polymers [91-95]. Mechanical testing is a way to determine properties such as strength, stiffness and strain at break of polymeric materials. 

From this discussion, it is obvious that a definite decision on the suitability of a material with a special thermal treatment cannot be made from the results of spectroscopic measurements only. However, in combination with mechanical tests, spectroscopy in the far infrared is a quick guide to the sample morphology and its properties at low temperatures. 

Mechanical tests for advanced composite materials conform in many respects to the conventional test typology used for traditional isotropic materials. Despite the complication associated with the heterogeneity of composite systems, the interface between fiber and matrix, and the anisotropy at the micro- and macroscopic levels, the same characteristic property definitions generally used for conventional materials can be identified for these novel materials. In some cases additional constants are required and some differences in nomenclature are introduced especially when no isotropic counterpart exists. 

ASTM A370-1968, Methods and Definitions for Mechanical Testing and Steel Products, IBR approved for 1926.1001(f). 

This is a standard Charpy specimen as described in American Society of Testing and Materials A 370, Methods and Definitions for Mechanical Testing of Steel Products (available at each Regional Office of the Occupational Safety and Health Administration). The purpose of this requirement is to reduce the tendency of brittle fracture associated with dynamic loading, low temperature operation, and stress raisers which cannot be entirely avoided on welded structures. 

Mechanical testing procedures in common use involve other patterns of stress history than the simple creep and relaxation experiments on which the definitions of the transient viscoelastic functions are based, and the sinusoidally varying stress which is inherent in the definitions of the so-called dynamic properties. Certain relations between the behavior under coniplicated conditions and the basic viscoelastic functions are presented here together with some related problems. They are limited to linear viscoelastic systems and hence small strains, but in some cases could be extended to describe larger deformations, especially for simple extension. 

ASTM A370-10, Standard Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM International West Conshohocken, PA. 

Note, these definitions do not quantify the extent of degradation by any of the pathways they only indicate of the mechanism that is operating to promote degradation. While this is acceptable in a scientific sense to define a process or mechanism, the definitions do not meet or satisfy the requirement for environmentally acceptable degradable and biodegradable polymers, which, in the minds of legislators and lay people, is the key issue. To satisfy this very practical requirement, specifications for acceptability have to be set and monitored by standard testing protocols, based on the above definitions, which will be discussed later. 

The definition of crack initiation has been a contentious issue in the formation of the DCB test standards. In line with the mode I test published for fiber-reinforced polymer composites (ISO 2001), three different definitions of crack initiation have been established and are now embodied in the BS and ISO standards. The first relates to the instant when the load-displacement trace deviates from linearity. This definition is termed the nonlinear (NL) initiation point. The second relates to the point when the crack is seen to grow ahead of the initial precrack. This definition is termed the visual (VIS) initiation point. Third, in line with earlier fracture mechanics test standards, initiation has also been defined as corresponding to when the initial compliance of the test specimen has increased by 5%. This is termed the 5% offset value. To limit the potential magnitude of this value, it is a requirement that it precedes the point of maximum load. This initiation point is therefore called the Max/5% initiation point the value taken is the one occurring first (the max point or the 5% offset point). 

The mechanical properties of rigid foams vary considerably from those of flexible foams. The tests used to characterize these two classes of foams are, therefore, quite different, and the properties of interest from an application standpoint are also quite different. In this discussion the ASTM definition of rigid and flexible foams given earlier is used. 

Slow Strain-Rate Test In its present state of development, the results from slow strain-rate tests (SSRT) with electrochemical monitoring are not always completely definitive but, for a short-term test, they do provide considerable useful SCC information. Work in our laboratory shows that the SSRT with electrochemical monitoring and the U-bend tests are essentially equivalent in sensitivity in finding SCC. The SSRT is more versatile and faster, providing both mechanical and electrochemical feedback during testing. 

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