DBT 209 METALS TESTING IMPACT TEST THE BEND

DBT 209 METALS TESTING IMPACT TEST

THE BEND TEST FOR BRITTLE MATERIALS Ø Ø Ø Bend test - Application of a force to the center of a bar that is supported on each end to determine the resistance of the material to a static or slowly applied load. Flexural strength or modulus of rupture -The stress required to fracture a specimen in a bend test. Flexural modulus - The modulus of elasticity calculated from the results of a bend test, giving the slope of the stress-deflection curve.

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 18 The stress-strain behavior of brittle materials compared with that of more ductile materials

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 19 (a) The bend test often used for measuring the strength of brittle materials, and (b) the deflection δ obtained by bending

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 20 Stressdeflection curve for Mg 0 obtained from a bend test

STRAIN RATE EFFECTS AND IMPACT BEHAVIOR Ø Impact test - Measures the ability of a material to absorb the sudden application of a load without breaking. Ø Impact energy - The energy required to fracture a standard specimen when the load is applied suddenly. Ø Impact toughness - Energy absorbed by a material, usually notched, during fracture, under the conditions of impact test. Ø Fracture toughness - The resistance of a material to failure in the presence of a flaw.

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 26 The impact test: (a) The Charpy and Izod tests, and (b) dimensions of typical specimens

Izod Charpy

PROPERTIES OBTAINED FROM THE IMPACT TEST Ø Ductile to brittle transition temperature (DBTT) - The temperature below which a material behaves in a brittle manner in an impact test. Ø Notch sensitivity - Measures the effect of a notch, scratch, or other imperfection on a material’s properties, such as toughness or fatigue life.

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 27 Results from a series of Izod impact tests for a super-tough nylon thermoplastic polymer

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 28 The Charpy V-notch properties for a BCC carbon steel and a FCC stainless steel. The FCC crystal structure typically leads top higher absorbed energies and no transition temperature

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 29 The area contained within the true stress-true strain curve is related to the tensile toughness. Although material B has a lower yield strength, it absorbs a greater energy than material A. The energies from these curves may not be the same as those obtained from impact test data

MICROSTRUCTURAL FEATURES OF FRACTURE IN METALLIC MATERIALS Ø Transgranular - Meaning across the grains (e. g. , a transgranular fracture would be fracture in which cracks would go through the grains). Ø Microvoids - Development of small holes in a material. Ø Intergranular - In between grains or along the grain boundaries. Ø Chevron pattern - A common fracture feature produced by separate crack fronts propagating at different levels in the material.

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 36 When a ductile material is pulled in a tensile test, necking begins and voids form – starting near the center of the bar – by nucleation at grain boundaries or inclusions. As deformation continues a 45° shear lip may form, producing a final cup and cone fracture

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 37 Dimples form during ductile fracture. Equiaxed dimples form in the center, where microvoids grow. Elongated dimples, pointing toward the origin of failure, form on the shear lip

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 38 Scanning electron micrographs of an annealed 1018 steel exhibiting ductile fracture in a tensile test. (a) Equiaxed dimples at the flat center of the cup and cone, and (b) elongated dimples at the shear lip (x 1250)

Figure 6. 39 Scanning electron micrograph of a brittle fracture surface of a quenched 1010 steel (x 5000). (Courtesy of C. W. Ramsay. )

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 40 The Chevron pattern in a 0. 5 -in. -diameter quenched 4340 steel. The steel failed in a brittle manner by an impact blow

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 41 The Chevron pattern forms as the crack propagates from the origin at different levels. The pattern points back to the origin

MICROSTRUCTURAL FEATURES OF FRACTURE IN CERAMICS, GLASSES, AND COMPOSITES Ø Ø Conchoidal fracture - Fracture surface containing a very smooth mirror zone near the origin of the fracture, with tear lines comprising the remainder of the surface. Delamination - The process by which different layers in a composite will begin to debond.

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 42 Scanning electron micrographs of fracture surfaces in ceramics. (a) The fracture surface Al 203, showing the cleavage faces (x 1250), and (b) the fracture surface of glass, showing the mirror zone (top) and tear lines characteristic of conchoidal fracture (x 300)

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 6. 43 Fiberreinforced composites can fail by several mechanisms. (a) Due to weak bonding between the matrix and fibers, fibers can pull out of the matrix, creating voids. (b) if the individual layers of the matrix are poorly bonded, the matrix may delaminate, creating voids