Mechanical Properties
The mechanical properties of a material are tho properties that involve a reaction to an applied load. The mechanical properties of metals determine the range of ufulness of a material and establish the rvice life that can be expected. Mechanical properties are also ud to help classify and identify material. The most common properties considered are strength, ductility, hardness, impact resistance, and fracture toughness.
Most structural materials are anisotropic, which means that their material properties vary with orientation. The variation in properties can be due to directionality in the microstructure (texture) from forming or cold working operation, the controlled alignment of fiber reinforcement and a variety of other caus. Mechanical properties are generally specific to product form such as sheet, plate, extrusion, casting, forging, and etc. Additionally, it is common to e mechanical property listed by the directional grain structure of the material. In products such as sheet and plate, the rolling direction is called the longitudinal direction, the width of the product is called the transver direction,
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and the thickness is called the short transver direction. The grain orientations in standard wrought forms of metallic products are shown the image.
The mechanical properties of a material are not constants and often change as a function of temperature, rate of loading, and other conditions. For example, temperatures below room temperature generally cau an increa in strength properties of metallic alloys; while ductility, fracture toughness, and elongation usually decrea. Temperatures above room temperature usually cau a decrea in the strength properties of metallic alloys. Ductility may increa or decrea with increasing temperature depending on the same variablesevent是什么意思
quicksimIt should also be noted that there is often significant variability in the values obtained when measuring mechanical properties. Seemingly identical test specimen from the same lot of material will often produce considerable different results. Therefore, multiple tests are commonly conducted to determine mechanical properties and values reported can be an average value or calculated statistical minimum value. Also, a range of values are sometimes reported in order to show variability.
Loading
The application of a force to an object is known as loading. Materials can be subjected to many different loading scenarios and a material’s performance is dependant on the loading conditions. There are five fundamental loading conditions; tension, compression, bending, shear, and torsion. Tension is the type of loading in which the two ctions of material on either side of a plane tend to be pulled apart or elongated. Compression is the rever of tensile loading and involves pressing the material together. Loading by bending involves applying a load in a manner that caus a material to curve and results i
n compressing the material on one side and stretching it on the other. Shear involves applying a load parallel to a plane which caud the material on one side of the plane to want to slide across the material on the other side of the plane. Torsion is the application of a force that caus twisting in a material. jourdan
motorbikeIf a material is subjected to a constant force, it is called static loading. If the loading of the material is not constant but instead fluctuates, it is called dynamic or cyclic loading. The way a material is loaded greatly affects its mechanical properties and largely determines how, or if, a component will fail; and whether it will show warning signs before failure actually occurs.
Stress全美音乐奖2010
The term stress (s) is ud to express the loading in terms of force applied to a certain cross-ctional area of an object. From the perspective of loading, stress is the applied force or system of forces that tends to deform a body. From the perspective of what is happening within a material, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. The stress distribution may or may not be uniform, depending on the nature of the loading condition. For example, a bar loaded in pure tension will esntially have a uniform tensile stress distribution. However, a bar loa
noblesded in bending will have a stress distribution that changes with distance perpendicular to the normal axis.
Strain
Strain is the respon of a system to an applied stress. When a material is loaded with a force, it produces a stress, which then caus a material to deform. Engineering strain is defined as the amount of deformation in the direction of the applied force divided by the initial length of the material. This results in a unitless number, although it is often left in the unsimplified form, such as inches per inch or meters per meter. For example, the strain in a bar that is being stretched in tension is the amount of elongation or change in length divided by its original length. As in the ca of stress, the strain distribution may or may not be uniform in a complex structural element, depending on the nature of the loading condition.
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cheryl coleIf the stress is small, the material may only strain a small amount and the material will return to its original size after the stress is relead. This is called elastic deformation, becau like elastic it returns to its unstresd state. Elastic deformation only occurs in a material when stress are lower than a critical stress called the yield strength. If a material is loaded beyond it elastic limit, the material will remain in a deformed condition after the load is removed. This is called plastic deformation.
