a physical injury or wound produced by an external or internal force external force/s acting on internal tissue ability of tissue to resist a load internal resistance to an external load extent of deformation of tissue under loading change in shape of the tissue property that allows a tissue to return to normal following deformation deformation of tissues that exists after the load is romoved deformation of tissues that occurs with application of a constant load over time exceeding the ability to withstand stress and strain, causing tissue to break down can deform significantly before failing and consequently have a longer plastic area can deform very little before failure five type of tissue loading(stress) compression tension shearing bending torsion -produced by external loads applied toward one another on opposite surfaces in opposite directions -shortens and widens a structure -commonly causes arthritic changes in cartilage, fracture, and contusions -the force that pulls or streches tissue -generated in response to equal and opposite external loads that pull a structure apart -structure elongates -the structure elongates and tensile stress and strain result -muscle strains and ligament sprains both occur doe to increased tension -occurs when equal but not directly opposite loads are applied to opposing surfaces, forcing thouse surafaces to move in a parallel directions relative to one another. -injury occurs once shearing has exceeded the inherant strength of a tissue -occurs in three ways:
-the original axis is maintained while the convex side of the structure is elongated and subject to tension forces and the concave side is shortened and subject to compression forces -torsion loads caused by the twisting in opposite directions from opposite ends of a structure cause shear stress over the entire cross section of that structure -a stretch, tear, or rip in the muscle or its tendon -3 grades -some muscle fibers have been streched or actually torn -some tenderness and pain on active motion -movement is painful, but full range of motion is usually possible -a number of muscle fibers have been streched/actually torn -active contraction of the muscle is usually extremly painful -depression/divot may be felt in the muscle belly, where the tear is -decreased ROM, due to pain -complete rupture of a muscle in the area of the muscle belly at the point at which muscle becomes tendon or at the tendinous attachment to the bone -significant impairment or total loss of motion -intense pain, quickly diminishes because of nerve separation Where are Grade 3 muscle strains most common? -biceps tendon of the upper arm -in the Achilles heel cord -involuntary muscle contractions -occur most commonly in the calf, abdomen, or hamstrings muscle contraction in response to pain -involuntary muscle contraction characterized by alternate contraction and relaxation in rapid succession -type of muscle contraction characterized by constant contraction that lasts for a period of time -pain caused by overexertion in exercise -acute-onset muscle soreness -delayed-onset muscle soreness(DOMS) Acute-onset muscle soreness -accompanies fatigue --occurs during and immediatly after exercise Delayed-onset muscle soreness(DOMS) -most intense after 24-48 hours and then gradually subsides after 3 to 4 days -syndrome of a delayed muscle pain leading to increased muscle tension, swelling, stiffness, and resistance to stretching -very small tears in the muscle tissue
-disruption of teh connective tissue that holds muscle tendon fibers together -wavy, parallel, collagenous fibers that are organized into bundles surrounded by a gelatinous material that reduces friction The breaking point in a tendon occurs after ________ a 6-8% increase in the length
Mechanical Property Terms Credit: Ron Redwing As we can see in the above graphic, there are quite a few materials terms that are used when describing the properties of materials. In this lesson, we are going to define the above terms. It turns out that many of the above terms are related to the stress-strain curve of a material. What are stress and strain, and how are they related? Let us take a cylinder and stress it. To stress it, I would fix one end of the cylinder and pull from the other end as shown in the figure below.  Tensile Stress Credit: Callister According to Newton's third law, the cylinder will experience a force downward on the lower surface of the cylinder and an equal and opposite force on the upper surface of the cylinder. My cylinder has an original length of Io and surface area of Ao. As I pull on my material with the force F the cylinder will lengthen and the resulting length will be l. Stress, σ, is defined as the force divided by the initial surface area, σ=F/Ao. This pulling stress is called tensile stress. Strain is what results from this stress. Strain, ε, is defined as the change in length divided by the original length, ε=ΔI/Io. Before we proceed further with stress and strain, let's define some other types of stress. If instead of pulling on our material, we push or compress our cylinder we are introducing compressive stress. This is illustrated in the following figure: Compressive Stress Credit: Callister If instead of applying a force perpendicular to the surface, we apply parallel but opposite forces on the two surfaces we are applying a shear stress. This is illustrated in the following figure: Shear Stress Credit: Callister Stress related to shear is torsional stress. If we hold one end of our cylinder fixed and twist the other end as shown in the figure below, we are applying a torsional (or twisting) stress. Torsional Stress Credit: Callister |
What type of force is caused by twisting in opposite direction from the opposite ends of a structure?
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