Tensile testing of notched specimens

We now resume the example from page 121, using the stress-strain curve of AlSi 1 MgMn from figure 4.6. Taking the value of 7nss = 188.6 MPa and Young s modulus of = 66 200 MPa, we find from equation (4.5) 

These considerations show that the component does not fracture although it yields at the notch root. However, plastic deformation is confined to a small volume. The global deformation is thus small so that limited plastic flow in the notch root is also acceptable from this point of view. 

To summarise, it can be stated that in notched components the strongest material is not always the best choice since weaker materials have a larger ductility. This is even more important under cyclic loads, a fact to be discussed in chapter 10. 

In this section, we discuss the influence of a notch on a tensile test specimen. We compare an un-notched and a notched tensile specimen as shown in fig- 

We now discuss the differences between the two stress-strain curves  

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Besides crystallinity itself, the kind and amount of side chains is of importance for crazing. A schematic investigation of the influence of chain branches was performed in PE that were introduced via copolymerization [84], A long-chain branched low-density polyethylene (PE-LD) was compared to a linear low-density polyethylene (PE-LLD) with different short chains [85]. Type and concentration of the copolymers were chosen in order to attain the same density of 0.920 g/cm3 and melt flow rate of 25 g/10 min for all polymers. The ESC resistance was measured in a long-term tensile test of notched specimens at 50 °C in 10% Igepal solution. 

Tensile tests of notched specimens from plain and welded plate have been made to measure the notch sensitivity of aluminum-magnesium alloys at low temperatures. For the plain plate, specimens with four different notches, as shown in Fig. 2b were tested at room temperature and at -320 F. For the welded plate, Type I specimens from across the weld with the deep sharp notch machined in the center of the weld itself were tested at the same two temperatures. The results were compared with those obtained on standard 1/2 in. diameter tensile specimens (ASTM E8-57T). 

Stress crack resistance of PE materials is eharacterised by times-to-failure in long-term tensile tests on notched specimens not only in the above mentioned but also in many other technical papers. The phenome-... 

Elastic modulus and yield stress were measured by compression tests on 10x5x4 mm prisms cut out from hot pressed plates. The J-integral measurements (J-Aa curve) were performed from tensile tests on CT specimens of 48 x 40 x 4 mm size, with a closed loop controlled machine (Schenk-Trebel). The starting crack was made using a razor blade (notch radius < 50 pm) up to a depth ao of 10 mm. 

The presence of unintentional damage in short fiber reinforced compo.sitcs contributes to the relationship that appears to exist between the test results obtained with unnotched tensile tests and notched fracture toughness tests. A correlation is possible, since both these specimens fail in a similar manner where the failure is predominantly associated with the fiber-matrix interphase with little damage or yielding of the matrix beyond the... 

The notched tensile test specimens used in this investigation are shown in Fig. 1. For most tests, the notched specimens were used with a notch concentration factor of Kt — 6.3, as determined after Neuber [ ]. In one series of tests a of 15.0 was used. Each notched specimen was checked with a Jones Lamson optical comparator at 50 x. Only those specimens with notched dimensions within the specified tolerances were tested. 

From Figs. 2 and 3, it is clear that adjustment can be made to the alloy to obtain desired tensile properties and the NTS/UNTS ratios to satisfy the needs of a particular application. It is realized, of course, that the test result from a simple uniaxial tensile test of a notched specimen may not be completely valid for extending data to all applications ... 

There are several techniques to determine for a ceramic. The two main approaches are to use indentation or bending. In the bend test a notch is introduced, usually using a diamond-tipped copper cutting wheel, into the tensile side of the specimen as shown in Figure 16.13. In Figure I6.I3a the... 

Tensile and notch-tensile tests of AISI 304 were conducted at the four test temperatures listed above. In addition, two other variables, strain rate and thermal cycling, were introduced. The strain rates employed were those resulting from crosshead speeds of 0.005, 0.02 and 0.2 in. per min. at each test temperature. To determine the effect of thermal cycling on mechanical properties of AISI 304 in the absence of spontaneous martensitic transformation, one half of all the specimens were subjected to temperature cycling between 300° and 76°K (holding at 76°K) for a period of one year [2]. 

Table III. Results of Tensile Tests of Smooth and Notched Specimens... 

The NCTL test is a long-term tensile test on notched test specimens taken from a geomembrane sample. Small dumbbell specimens (Fig. 3.17) are punched from the geomembrane sample (along or crosswise to the direction of manufacture). Notching is carried out with a razor-blade. The depth of the notch is 20 % of specimen thickness. The stress-rupture curve is then determined in a long-term tensile test at (50 1) °C in a bath of... 

SEPB) test is thus a refinement of the SENB, to introduce a precrack. The specimen is held in a loading fixture which generates a Vickers indentation or a single notch at the eentre of the tensile surface of the specimen, which is then loaded in 4-point bend to failure, as in the SENB. The specimen must be made with accurately parallel faces and squared corners. 

Samples of type 301 stainless steel were obtained which had been cold-worked 42, 62, and 78. The chemical analyses of these steels are given in Table I. The chemistry was normal for AISI type 301, except that carbon was held to a maximum of 0.10 to minimize carbide precipitation during welding. Standard sheet specimens were prepared for tensile tests, while notched sheet specimens were used to determine notch tensile strength. A notch-acuity factor of about 6.3 was... 

ASTM F1473 describes test specimens from pipe and from the resiit This presentation will be focused on PENT testing of the resin from compression molded plaques. PENT is a sin e edge notch tensile test A representative specimen is shown in Figure 3. Other dimensions are given in the specification. In the specification a standard value of K = 0.468 MPa m has been established. This value was chosen to insure that all PE would fail by the mechanism of SCG at 80°C. If K is too high, the failure could occur by a complex combination of shear deformation and fiacture which is not the long time mode of failure that occurs under field conditions. The thickness of the compression... 

FIGURE 10.2 Mechanical failure tests (a) tensile test on dumbbell specimen (b) tensile test on ring specimen (c) notched crescent and trousers tear specimens (d) Izod impact test machine (Data from HaUinan, A. J., Jr., J. Qual. Tech., 25, 85, 1993) (e) motor-driven brittleness temperature tester. (Data from Book of Standards, ASTM, Baltimore, MD, 1958, 286,356.)... 

The concept of a ductile-to-brittle transition temperature in plastics is likewise well known in metals, notched metal products being more prone to brittle failure than unnotched specimens. Of course there are major differences, such as the short time moduli of many plastics compared with those in steel, that may be 30 x 106 psi (207 x 106 kPa). Although the ductile metals often undergo local necking during a tensile test, followed by failure in the neck, many ductile plastics exhibit the phenomenon called a propagating neck. Tliese different engineering characteristics also have important effects on certain aspects of impact resistance. 

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