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Jun 17, 2019 · Fracture strength, also known as breaking strength, is the stress at which a specimen fails via fracture. This is usually determined for a given specimen by a tensile test, which charts the stress-strain curve.
Fracture strength is the ability of a material to resist failure and is designated specifically according to the mode of applied loading, such as tensile, compressive, or bending.
- Overview
- Stress Concentrations Around Cracks
- Modes of Loading
- Stress Intensity Factor
- Fracture Toughness
- Initial Crack Size
- Plastic Zone Size
- Ductile vs. Brittle Fracture
- Static Fracture Analysis Methods
- Fatigue Crack Growth
Fracture mechanics is a methodology that is used to predict and diagnose failure of a part with an existing crack or flaw. The presence of a crack in a part magnifies the stress in the vicinity of the crack and may result in failure prior to that predicted using traditional strength-of-materials methods. The traditional approach to the design and a...
Cracks act as stress risers and cause the stress in the part to spike near the tip of the crack. As a simple example, consider the case of an elliptical crack in the center of an infinite plate: The theoretical value of stress at the tip of the ellipse is given by: where σ is the nominal stress and ρ is the radius of curvature of the ellipse, ρ = b...
There are three primary modes that define the orientation of a crack relative to the loading. A crack can be loaded in one mode exclusively, or it can be loaded in some combination of modes. The figure above shows the three primary modes of crack loading. Mode I is called the opening mode and involves a tensile stress pulling the crack faces apart....
The stress intensity factor is a useful concept for characterizing the stress field near the crack tip. For Mode I loading, the linear-elastic stresses in the direction of applied loading near an ideally sharp crack tip can be calculated as a function of the location with respect to the crack tip expressed in polar coordinates: A term K, called the...
A material can resist applied stress intensity up to a certain critical value above which the crack will grow in an unstable manner and failure will occur. This critical stress intensity is the fracture toughnessof the material. The fracture toughness of a material is dependent on many factors including environmental temperature, environmental comp...
Cracks and crack-like flaws are common in engineering materials. Cracks will typically form around pre-existing flaws which act as stress concentrations and which, upon high stress or fatigue, develop into full-fledged cracks. Many flaws are serious enough that they should be treated as cracks, and these include deep scratches, inclusions of foreig...
Plane-Stress vs. Plane-Strain
The size of the plastic zone is dependent on whether the part is considered to be in a plane-stress or a plane-strain condition. In plane-stress, the section is thin enough that the stresses through the thickness of the section are approximately constant. In plane-strain, stresses develop through the thickness of the section to resist contraction of the material and to keep the strain throughout the thickness approximately constant. The part can be considered to be in plane-strain if the thic...
Plastic Zone Size for Plane-Stress
Due to the sharp nature of the crack, there will always be a plastic zone just ahead of the crack tip. We can use the elastic stress field equations (discussed in a previous section) to solve for the theoretical distance from the crack tip at which the stresses are equal to the material's yield strength. The elastic stress field equation is: Setting the stress equal to the material's yield strength and solving for r gives the theoretical size of the plastic zone, rt: where Kapp is the stress...
Plastic Zone Size for Plane-Strain
The plastic zone size estimates described in the previous section apply to the plane-stress condition where the section is thin enough that the stresses through the thickness of the section are approximately constant. If the section is thick enough to be considered in plane-strain (i.e., stresses develop through the thickness of the section to resist contraction of the material and to keep the strain throughout the thickness approximately constant), then the size of the plastic zone is reduce...
There are two frames of reference when discussing ductile fracture versus brittle fracture. These frames of reference are the fracture mechanism and the fracture mode. When materials scientists talk about brittle fracture and ductile fracture, they are typically referring to the fracture mechanism, which describes the fracture event at a microscopi...
Static fracture analysis should be performed considering the peak load that the part is expected to see during its lifetime. In the static analysis methods, the load is steady and does not vary with time. On the other hand, fatigue crack growth analysiscan be used to consider crack growth due to a time-varying load. The loads over the entire servic...
This page on fracture mechanics covered the analysis of cracked parts under static load conditions (i.e., conditions with steady loads that do not vary with time). For the case where the load does vary with time, the stress intensity at the crack tip will also vary. The crack will grow in the case that the variance in stress intensity exceeds the m...
Fracture Strength. Fracture strength is the ability of a material to resist failure and is designated specifically according to the mode of applied loading, such as tensile, compressive, or bending. From: Orthodontic Applications of Biomaterials, 2017
Fig.1.1 Strength of uncracked and cracked plates. The thickness of each plate is the same. The forces required to break the four samples can be arranged in the following order: F4 < F3 < F1 < F2. Clearly the sizes of the defects at F3 and F4 are crucial to the strength of the structure.
Ultimate tensile strengths vary from 50 MPa for aluminum to as high as 3000 MPa for very high-strength steel. Fracture point: The fracture point is the point of strain where the material physically separates. At this point, the strain reaches its maximum value, and the material fractures, even though the corresponding stress may be less than ...
Feb 21, 2014 · A bone fracture or an osteotomy is a complete or incomplete break in the anatomic continuity of bone, which leads to mechanical instability of the bone. A fracture is accompanied by various degrees of injury to the surrounding soft tissues, including blood supply, and in most instances results in compromised function of the locomotor system.
