Sample sizes
According to ASTM A370, [12] the standard specimen size for Charpy impact testing is 10 mm × 10 mm × 55 mm. Subsize specimen sizes are: 10 mm × 7.5 mm × 55 mm, 10 mm × 6.7 mm × 55 mm, 10 mm × 5 mm × 55 mm, 10 mm × 3.3 mm × 55 mm, 10 mm × 2.5 mm × 55 mm. Details of specimens as per ASTM A370 (Standard Test Method and Definitions for Mechanical Testing of Steel Products).
According to EN 10045-1 (retired and replaced with ISO 148), [10] standard specimen sizes are 10 mm × 10 mm × 55 mm. Subsize specimens are: 10 mm × 7.5 mm × 55 mm and 10 mm × 5 mm × 55 mm.
According to ISO 148, [9] standard specimen sizes are 10 mm × 10 mm × 55 mm. Subsize specimens are: 10 mm × 7.5 mm × 55 mm, 10 mm × 5 mm × 55 mm and 10 mm × 2.5 mm × 55 mm.
According to MPIF Standard 40, [13] the standard unnotched specimen size is 10 mm (±0.125 mm) x 10 mm (±0.125 mm) x 55 mm (±2.5 mm).
Welding is a fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melt the parts together and allow them to cool, causing fusion. Common alternative methods include solvent welding using chemicals to melt materials being bonded without heat, and solid-state welding processes which bond without melting, such as pressure, cold welding, and diffusion bonding.
Ductility refers to the ability of a material to sustain significant plastic deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversible upon removing the stress. Ductility is a critical mechanical performance indicator, particularly in applications that require materials to bend, stretch, or deform in other ways without breaking. The extent of ductility can be quantitatively assessed using the percent elongation at break, given by the equation:
Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially, it is called a shear crack, slip band, or dislocation.
In mechanics, compressive strength is the capacity of a material or structure to withstand loads tending to reduce size. In other words, compressive strength resists compression, whereas tensile strength resists tension. In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing. Toughness is the strength with which the material opposes rupture. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. This measure of toughness is different from that used for fracture toughness, which describes the capacity of materials to resist fracture. Toughness requires a balance of strength and ductility.
A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a sharp snapping sound.
Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.
In materials science and solid mechanics, residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed. Residual stress may be desirable or undesirable. For example, laser peening imparts deep beneficial compressive residual stresses into metal components such as turbine engine fan blades, and it is used in toughened glass to allow for large, thin, crack- and scratch-resistant glass displays on smartphones. However, unintended residual stress in a designed structure may cause it to fail prematurely.
In mechanics, an impact is when two bodies collide. During this collision, both bodies decelerate. The deceleration causes a high force or shock, applied over a short time period. A high force, over a short duration, usually causes more damage to both bodies than a lower force applied over a proportionally longer duration.
In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest fracture toughness value which is a material property. The critical value of stress intensity factor in mode I loading measured under plane strain conditions is known as the plane strain fracture toughness, denoted . When a test fails to meet the thickness and other test requirements that are in place to ensure plane strain conditions, the fracture toughness value produced is given the designation . Fracture toughness is a quantitative way of expressing a material's resistance to crack propagation and standard values for a given material are generally available.
The Izod impact strength test is an ASTM standard method of determining the impact resistance of materials. A pivoting arm is raised to a specific height and then released. The arm swings down hitting a notched sample, breaking the specimen. The energy absorbed by the sample is calculated from the height the arm swings to after hitting the sample. A notched sample is generally used to determine impact energy and notch sensitivity.
Liquid metal embrittlement is a phenomenon of practical importance, where certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when exposed to specific liquid metals. Generally, tensile stress, either externally applied or internally present, is needed to induce embrittlement. Exceptions to this rule have been observed, as in the case of aluminium in the presence of liquid gallium. This phenomenon has been studied since the beginning of the 20th century. Many of its phenomenological characteristics are known and several mechanisms have been proposed to explain it. The practical significance of liquid metal embrittlement is revealed by the observation that several steels experience ductility losses and cracking during hot-dip galvanizing or during subsequent fabrication. Cracking can occur catastrophically and very high crack growth rates have been measured.
The three-point bending flexural test provides values for the modulus of elasticity in bending , flexural stress , flexural strain and the flexural stress–strain response of the material. This test is performed on a universal testing machine with a three-point or four-point bend fixture. The main advantage of a three-point flexural test is the ease of the specimen preparation and testing. However, this method has also some disadvantages: the results of the testing method are sensitive to specimen and loading geometry and strain rate.
George Rankin Irwin was an American scientist in the field of fracture mechanics and strength of materials. He was internationally known for his study of fracture of materials.
Embrittlement is a significant decrease of ductility of a material, which makes the material brittle. Embrittlement is used to describe any phenomena where the environment compromises a stressed material's mechanical performance, such as temperature or environmental composition. This is oftentimes undesirable as brittle fracture occurs quicker and can much more easily propagate than ductile fracture, leading to complete failure of the equipment. Various materials have different mechanisms of embrittlement, therefore it can manifest in a variety of ways, from slow crack growth to a reduction of tensile ductility and toughness.
Polymer characterization is the analytical branch of polymer science.
Slow strain rate testing (SSRT), also called constant extension rate tensile testing (CERT), is a popular test used by research scientists to study stress corrosion cracking. It involves a slow dynamic strain applied at a constant extension rate in the environment of interest. These test results are compared to those for similar tests in a, known to be inert, environment. A 50-year history of the SSRT has recently been published by its creator. The test has also been standardized and two ASTM symposia devoted to it.
The notch tensile strength (NTS) of a material is the value given by performing a standard tensile strength test on a notched specimen of the material. The ratio between the NTS and the tensile strength is called the notch strength ratio (NSR).
In mechanical engineering and materials science, a notch refers to a V-shaped, U-shaped, or semi-circular defect deliberately introduced into a planar material. In structural components, a notch causes a stress concentration which can result in the initiation and growth of fatigue cracks. Notches are used in materials characterization to determine fracture mechanics related properties such as fracture toughness and rates of fatigue crack growth.
