More D In addition, foundation soils are often compacted to improve their engineering properties. Laboratory compaction tests provide the basis for determining the percent compaction and molding water content needed to achieve the required engineering properties, and for controlling construction to assure that the required compaction and water contents are achieved. If the required degree of compaction is substantially less than the modified maximum dry unit weight using this test method, it may be practicable for testing to be performed using Test Method D and to specify the degree of compaction as a percentage of the standard maximum dry unit weight. Since more energy is applied for compaction using this test method, the soil particles are more closely packed than when D is used. The general overall result is a higher maximum dry unit weight, lower optimum moisture content, greater shear strength, greater stiffness, lower compressibility, lower air voids, and decreased permeability.
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More E Background information on the rationale for employing the fracture mechanics approach in the analyses of creep crack growth data is given in 11, 13, Attention must be given to the proper selection and control of temperature and environment in research studies and in generation of design data. Thus, the appropriate correlation will enable exchange and comparison of data obtained from a variety of specimen configurations and loading conditions.
Moreover, this feature enables creep crack growth data to be utilized in the design and evaluation of engineering structures operated at elevated temperatures where creep deformation is a concern. See It is therefore necessary to keep the component dimensions in mind when selecting specimen thickness, geometry and size for laboratory testing. For these reasons, the scope of this standard is restricted to the use of specimens shown in Annex A1 and the validation criteria for these specimens are specified in This transient region, especially in creep-brittle materials, can be present for a substantial fraction of the overall life Criteria are provided in this standard to quantify this region as an initial crack growth period see 1.
Localized damage in a small zone around the crack tip is permissible, but not in a zone that is comparable in size to the crack size or the remaining ligament size. Creep damage for the purposes here is defined by the presence of grain boundary cavitation. Creep crack growth is defined primarily by the growth of intergranular time-dependent cracks.
Crack tip branching and deviation of the crack growth directions can occur if the wrong choice of specimen size, side-grooving and geometry is made see 8. The criteria for geometry selection are discussed in 5. Scope 1. The solutions presented in this test method are validated for base material i.
The CCI time, t0. Two types of material behavior are generally observed during creep crack growth tests; creep-ductile and creep-brittle In creep-brittle materials, creep crack growth occurs at low creep ductility. Consequently, the time-dependent creep strains are comparable to or dominated by accompanying elastic strains local to the crack tip. Under such steady state creep-brittle conditions, Ct or K could be chosen as the correlating parameter The initial transient region where elastic strains dominate and creep damage develops and in the steady state region where crack grows proportionally to time.
Steady-state creep crack growth rate behavior is covered by this standard. In addition, specific recommendations are made in Such conditions are distinct from the conditions of small-scale creep and transition creep In the case of extensive creep, the region dominated by creep deformation is significant in size in comparison to both the crack length and the uncracked ligament sizes.
In small-scale-creep only a small region of the un-cracked ligament local to the crack tip experiences creep deformation. This distance is given as 0. It has been shown that this initial period which exists at the start of the test could be a substantial period of the test time. During this early period the crack tip undergoes damage development as well as redistribution of stresses prior reaching steady state.
Recommendation is made to correlate this initial crack growth period defined as t0. The clevis setup is shown in Fig. Additional geometries which are valid for testing in this procedure are shown in Fig.
In Fig. Recommended loading for the tension specimens is pin-loading. The configurations, size range are given in Table A1. Specimen selection will be discussed in 5. Specimen size, geometry, crack length, test duration and creep properties will affect the state-of-stress at the crack tip and are important factors in determining crack growth rate.
A recommended size range of test specimens and their side-grooving are given in Table A1. It has been shown that for this range the cracking rates do not vary for a range of materials and loading conditions Suggesting that the level of constraint, for the relatively short term test durations less than one year , does not vary within the range of normal data scatter observed in tests of these geometries.
However, it is recommended that, within the limitations imposed on the laboratory, that tests are performed on different geometries, specimen size, dimensions and crack size starters. In all cases a comparison of the data from the above should be made by testing the standard C T specimen where possible.
It is clear that increased confidence in the materials crack growth data can be produced by testing a wider range of specimen types and conditions as described above. In cases where residual stresses exist, the effect can be significant when test specimens are taken from material that characteristically embodies residual stress fields or the damaged material, or both.
For example, weldments, or thick cast, forged, extruded, components, plastically bent components and complex component shapes, or a combination thereof, where full stress relief is impractical. Specimens taken from such component that contain residual stresses may likewise contain residual stresses which may have altered in their extent and distribution due to specimen fabrication. Extraction of specimens in itself partially relieves and redistributes the residual stress pattern; however, the remaining magnitude could still cause significant effects in the ensuing test unless post-weld heat treatment PWHT is performed.
Otherwise residual stresses are superimposed on applied stress and results in crack-tip stress intensity that is different from that based solely on externally applied forces or displacements. This would produce conservative estimates for life assessment and non-conservative calculations for design purposes. It should also be noted that distortion during specimen machining can also indicate the presence of residual stresses.
No specific allowance is included in this standard for dealing with these variations. This is done by comparing data from recommended test configurations. Nevertheless, use of other geometries are applicable by this method provided data are compared to data obtained from standard specimens as identified in Table A1. The inch-pound units given in parentheses are for information only. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
More D These PTFE resins are homopolymers of tetrafluoroethylene, or, in some cases, modified homopolymers containing not more than one percent by weight of other fluoromonomers. The materials included herein do not include mixtures of PTFE resin with additives such as colorants, fillers or plasticizers; nor do they include reprocessed or reground resin or any fabricated articles. Included are specimen preparation, test methods and requirements for materials, melting characteristics, bulk density, particle size, water content, standard specific gravity, thermal instability index, and mechanical tensile properties. This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application.