Tham khảo tài liệu 'metal_foams episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Characterization methods 29 between 5 and 30 of the mean while that in the compressive strength is typically between 5 and 15 . Data for the compressive strength of metallic foams are presented in Chapter 4. Uniaxial tension testing Uniaxial tension tests can be performed on either waisted cylinder or dogbone specimens. The specimens should be machined to the shape specified in ASTM E8-96a to avoid failure of the specimen in the neck region or at the grips. The minimum dimension of the specimen the diameter of the cylinder or the thickness of the dogbone should be at least seven times the cell size to avoid specimen cell size effects. Gripping is achieved by using conventional grips with sandpaper to increase friction or better by adhesive bonding. Displacement is best measured using an extensometer attached to the waisted region of the specimen. A typical tensile stress-strain curve for an aluminum foam is shown in Figure . Young s modulus is measured from the unloading portion of the stress-strain curve as in uniaxial compression testing. The tensile strength is taken as the maximum stress. Tensile failure strains are low for aluminum foams in the range of . The standard deviation in the tensile strengths of aluminum foams like that of the compressive strength is between 5 and 15 of the mean. Typical data for the tensile strength of metallic foams are given in Chapter 4. Figure Stress-strain curve from a uniaxial tension test on a dogbone specimen of a closed-cell aluminum foam 8 dense Alporas from Andrews et al. 1999a 30 Metal Foams A Design Guide Shear testing The shear modulus of metallic foams is most easily measured by torsion tests on waisted cylindrical specimens. The specimens should be machined to the shape of ASTM E8-96a to avoid failure of the specimen in the neck region or at the grips. The minimum dimension of the specimen the diameter of the cylinder should be at least seven times the cell size to avoid specimen cell size .
