Tensile testing, wood

The principal type of shear test specimen used in the industry, the lap shear specimen, is 2.54 cm wide and has a 3.23-cm overlap bonded by the adhesive. Adherends are chosen according to the industry aluminum for aerospace, steel for automotive, and wood for constmction appHcations. Adhesive joints made in this fashion are tested to failure in a tensile testing machine. The temperature of test, as weU as the rate of extension, are specified. Results are presented in units of pressure, where the area of the adhesive bond is considered to be the area over which the force is appHed. Although the 3.23-cm ... 

Even plastics with fairly linear stress-strain curves to failure, for example short-fiber reinforced TSs (RPs), usually display moduli of rupture values that are higher than the tensile strength obtained in uniaxial tests wood behaves much the same. Qualitatively, this can be explained from statistically considering flaws and fractures and the fracture energy available in flexural samples under a constant rate of deflection as compared to tensile samples under the same load conditions. These differences become less as the... 

To determine the quantitative effects of this consolidation procedure, fabric disks cut from the extracted degraded fabric were used as substrates. These fabrics were torn on an Instron tensile testing machine as described earlier and patched with six applications of either the 0.1% dyed wood pulp or the 0.05% dyed Cellunier P slurry. The samples were then torn again on the Instron tester. The average breaking strengths and add-ons of the samples after six passes with slurry are reported in Table IV. A typical tom fabric and a patched fabric are shown in Figures 6 and 7. 

ASTM D-1344 describes a cross-lap specimen of the type shown in Fig. 2d for determining tensile properties of adhesive bonds. Wood, glass, sandwich, and honeycomb materials have been tested as samples in this general configuration. Even under the best of circumstances, one would not anticipate the stress distribution in such a case to be very uniform. The exact stress distribution is highly dependent on the relative flexibilities of both the cross beams and the adhesive. Certainly, caution must be exercised when comparing tensile strength from this test with data obtained from other tensile tests. Probably for these reasons, this test is scheduled by ASTM for discontinuation. 

Zimmermann et al. [134] have used cellulose fibrils obtained from sulphite wood pulp to reinforce water soluble polymers such as polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC). The mechanical properties of these nanocomposites were measured by tensile tests showing that the addition of fibrils increase the modulus of elasticity (E) up to three times and the tensile strength up to five times compared to the raw polymer. Zimmermann et al. [135] have determined the E values and the hardness of cellulose/HPC nanocomposites using nanoindentation technique. The results showed that the E values measured by nanoindentation were from two to three times higher than the E values measured by means of tensile tests. Stauss et al. [136] have explained that differences between tensile test and indentation results are due to the fact that they do not test the same material volumes and regions. The large volume used in tensile test includes defects such as pores, cracks and impurities. 

It has been mentioned earlier that Soden and McLeish employed the classical tensor calculus to compute the effects of axis rotation and thereby to deduce the shear strength of balsa wood from the results of off-axis tensile tests. 

A very popular tensile test is the pi-tensile test, described in ASTM D897-78. This test can be used for wood-to-wood or metal-to-metal bonds. 

Figure 2. The pi-tensile test specimen for (a) wood-to-wood and (b) metal-to-metal bonds.

The tensile test is the experimental stress-strain test method most widely employed to characterize the mechanical properties of materials like plastics, metals, and wood. From any complete test record one can obtain important information concerning a material s elastic properties, the character and extent of its plastic deformation, and its yield and tensile strengths and toughness. That so much information can be obtained from one test of a material justifies its extensive use. To provide a framework for the varied responses to tensile loading in load-bearing materials that occur, several stress-strain plots, reflecting different deformation characteristics, will be examined. 

Plastics such as short-fiber reinforced plastics with fairly linear stress-strain curves to failure usually display moduli of rupture values that are higher than the tensile strength obtained in uniaxial tests wood... 

Note Plate of 13 nun (0.5 in.) thickness was heat treated as indicated. Tensile testing after exposure was performed without removal of suifoce oxidation. Source V Petersen, J. Guernsey, and R. Buehl, Manufacturing Procedures for a New High-Strength Beta Titamum AUoy Having Superior Formahility, AFML-TR-69-171,1969 R Wood, reported in Titanium Alloys, MClC-72-11,1972,p 153... 

Although shear testing may be more commonly used, stressing perpendicular to the glueline may be called for at times. The following two general-purpose tensile test standards can be used with various substrates, including metal, wood, and plastics ... 

ASTM list two specifications for the tensile testing of butt joints. The first, ASTM D 897-78 uses short, stubby, circular specimens of metal (or wood) with a cross-sectional area of 1 in, while the second (ASTM D 2095-72) allows for longer specimens of metal or reinforced plastics. For the latter test, specimens (round or square) should be prepared according to ASTM D 2094-69 which designates alignment tolerances and fixtures to minimize misalignment problems. 

ISO 5893 2002 Rubber and plastics test equipment - Tensile, flexural and compression types (constant rate of traverse) - Specification ISO 6237 2003 Adhesives - Wood-to-wood adhesive bonds - Determination of shear strength by tensile loading... 

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