Stress–strain curve - Wikipedia
If you want to understand it in simple terms then,with the help of an example, If i pull a rubber band within its limits of elaticity then the amount of force in unit. Stress-strain Relationship. To measure the mechanical properties of any material , we find the relationship between the stress and strain by conducting a test. As a result, the differences between stress, strain and structures formed stress and strain and allows them to investigate relationships among stress, strain and deformational structures. Now, what are the 2 types of permanent deformation?.
The appearance of the yield point is associated with pinning of dislocations in the system. Specifically, solid solution interacts with dislocations and acts as pin and prevent dislocation from moving.
Therefore, the stress needed to initiate the movement will be large. As long as the dislocation escape from the pinning, stress needed to continue it is less. After the yield point, the curve typically decreases slightly because of dislocations escaping from Cottrell atmospheres. As deformation continues, the stress increases on account of strain hardening until it reaches the ultimate tensile stress. Until this point, the cross-sectional area decreases uniformly and randomly because of Poisson contractions.
The actual fracture point is in the same vertical line as the visual fracture point. However, beyond this point a neck forms where the local cross-sectional area becomes significantly smaller than the original.
If the specimen is subjected to progressively increasing tensile force it reaches the ultimate tensile stress and then necking and elongation occur rapidly until fracture.
If the specimen is subjected to progressively increasing length it is possible to observe the progressive necking and elongation, and to measure the decreasing tensile force in the specimen. The appearance of necking in ductile materials is associated with geometrical instability in the system.Concept of Stress - Stress and Strain - Strength of Materials
Due to the natural inhomogeneity of the material, it is common to find some regions with small inclusions or porosity within it or surface, where strain will concentrate, leading to a locally smaller area than other regions. For strain less than the ultimate tensile strain, the increase of work-hardening rate in this region will be greater than the area reduction rate, thereby make this region harder to be further deform than others, so that the instability will be removed, i.
However, as the strain become larger, the work hardening rate will decreases, so that for now the region with smaller area is weaker than other region, therefore reduction in area will concentrate in this region and the neck becomes more and more pronounced until fracture.
After the neck has formed in the materials, further plastic deformation is concentrated in the neck while the remainder of the material undergoes elastic contraction owing to the decrease in tensile force.
The stress-strain curve for a ductile material can be approximated using the Ramberg-Osgood equation.
No, it isn't currently changing shape. Does it have structure? Yes, there is a fold.
Analogs, however, are difficult to scale appropriately both in time and space to the gigantic scale on which geologic structures form. Students may still have difficulty understanding the tremendous scale of forces needed to bend or break rock and the long time scales involved to generate structures.
Make sure that you make it clear to your students that these pitfalls exist.
More detailed ideas for analogs are available at Teaching Structural Geology analog materials web page. Once students have mastered the connections among stress, strain and structure, I develop a 3 x 2 table of different structures that form under differing stress and strain conditions.
I then proceed to fill out the table with students' help. Let's look at what features are found under different stress conditions and with different styles of strain. We'll do this by making a table. What are the three types of stress?
Stress and Strain
Compression, tension, and shearing. Now, what are the 2 types of permanent deformation? Let's make a table that is three columns by two rows and fill it in with appropriate structures! When we are finished, we should have 6 kinds of deformation features. Different conditions lead to different deformation styles There are many factors that contribute to the style of the deformation in a rock, including pressure, temperature, rock composition, presence or absence of fluids, type of stress, rate of stress, and others.
However, the type of stress, the rate of stress and the temperature may be the most critical factors for most introductory students.
What controls how it will deform? Cold Silly Putty is easy to break, but warm Silly Putty is very plastic. If I pull it apart quickly it breaks, but if I pull it slowly, it stretches deforms plastically. Finally, pick a strong student, and have him or her try to break the silly putty using compressive stress. As you can see, this is almost impossible.
Now have a student try to break it using tension. This is much easier. Most materials are more easily broken or otherwise deformed in tension than in compression; we say that they are weaker in tension, or stronger in compression. Temperature, strain rate, and type of stress are also key factors in deformation within glaciers. This provides a an opportunity to revisit these concepts later in the term. Relating faults to stress - hanging walls, footwalls, and different types of faults One of the goals of structural geology is to relate the nature of deformation to the stress that caused it.
Therefore, it is important that students be able to distinguish between normal faults generated by tension and reverse faults generated by compression.
Wooden blocks are a valuable tool for teaching about normal and reverse faults. Using three blocks cut on an angle, horsts and grabens can be generated. Pull the blocks apart to create a graben; push them together to make a horst. The advantage of using 3 blocks is that students can see that it is not the orientation of the fault that matters, but the movement on the fault. Because they can see whether I am extending or compressing the blocks, they develop an intuitive sense of the difference between normal and reverse faults.
However, students typically still need to learn the difference between the hanging wall and footwall of a fault to be able to accurately determine whether a fault is normal or reverse and what kind of stress caused it.
Faults are places where rocks have been broken and offset. It is not uncommon for fluids to have flowed along the break during deformation, leaving valuable minerals along the fault. As a result, many mines are constructed along fault surfaces. Because of this, one side of the fault is called the hanging wall the surface from which a miner's lantern would be hung and one side is called the footwall the surface on which the miner would walk.
Here's another way to think of it: To see this, put a point on the fault and draw a vertical arrow pointing up. This arrow points into the hanging wall. An arrow pointing straight down points into the footwall.
Take a look at the slide that shows the fault and arrows indicating movement. Some students think the footwall looks like a foot. See how the hanging wall is resting, or hanging, on the footwall? Once students understand the difference between a hanging wall and a footwall, most of them have little trouble remembering that in a reverse fault the hanging wall moves up, indicating compression, and in a normal fault the hanging wall moves down, indicating extension. As your students can see from these block models, horizontal forces can cause rocks to move along faults that are at an angle to the rock layering.
Given that idea, your students can use some basic trigonometric functions to examine the relationship between horizontal strain the amount of stretching or shortening in a horizontal direction and displacement on a fault surface the amount of movement on the fault itself. Since this relationship is dependent on the angle of the fault from horizontal, the angle of the fault is a critical component of how faults accommodate shortening or extension.
The Seattle fault is a large reverse fault that cuts across and underneath the Seattle, Washington, metropolitan area and its nearly 2 million residents.