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broken screw head
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<blockquote data-quote="ter01475" data-source="post: 146160" data-attributes="member: 7599"><p>The comparison of bending a wire vs the function of a screw is like comparing apples and oranges. The rules for and math involved for determining torque levels are not random. We do this all the time in the lab...why do you select the alloy that you use for bridge work?</p><p>One factor is strength or tensile strength, because we don't want the bridge to bend or fracture. We also use alloys that will flex but not fracture, and this is measured by modulus of elasticity...for instance a clasp. </p><p></p><p>To say they every time a load is applied to metal it deforms is not correct. We select alloys that can carry loads without deforming or fracturing. The same is true for most everything around us. Your deck in you home is built with lumber that has a tensile strength rating. The loads are once again figured out using math for the static load and the live load (people, furniture, and snow for some of us up north). Like screws we don't want the floor joists to bend or deform. What about your car...we you hit a bump in the road the car does not deform...hit a tree, which would be an overload for sure, it will bend and break. Your roof on your home...rigid and no deforming. There a huge difference in lumber for a home up north vs a home down south, due to snow loads.</p><p></p><p>There are ways to design screws that will bend, but won't fracture under a normal functional load. One design is what you see with the fastening screw for a Straumann Bone Level implant. There is the head with a bevel seat, then a long unthreaded shaft, and then the threaded portion. The bending movements are designed to happen in the unthreaded shaft. There is a point when the load exceeds the tensile strength of the alloy and it deforms. When that happens the unit has been stretched and it becomes loose. The worse outcome is it fractures. Most screws are designed to have a fracture point generally just below the head, so if there is an overload the broken portion can be removed and replaced.</p><p></p><p>For the subject of common sense....common sense told the citizens of Salem, Ma that there were some "ladies" in their town that should be burned at the stake...so what we might think as common sense is not always true. Take a look at a jumbo jet and watch them load it with freight... common sense tells me that there is no way that thing should be able to fly. How can a sailboat sail into the wind??</p><p></p><p>Well time to go out and get the boat clean for the weekend....I may re tighten all the screws and bolts the more I think about it, Have a great Memorial Day and HI to Chris...nice to see you here</p></blockquote><p></p>
[QUOTE="ter01475, post: 146160, member: 7599"] The comparison of bending a wire vs the function of a screw is like comparing apples and oranges. The rules for and math involved for determining torque levels are not random. We do this all the time in the lab...why do you select the alloy that you use for bridge work? One factor is strength or tensile strength, because we don't want the bridge to bend or fracture. We also use alloys that will flex but not fracture, and this is measured by modulus of elasticity...for instance a clasp. To say they every time a load is applied to metal it deforms is not correct. We select alloys that can carry loads without deforming or fracturing. The same is true for most everything around us. Your deck in you home is built with lumber that has a tensile strength rating. The loads are once again figured out using math for the static load and the live load (people, furniture, and snow for some of us up north). Like screws we don't want the floor joists to bend or deform. What about your car...we you hit a bump in the road the car does not deform...hit a tree, which would be an overload for sure, it will bend and break. Your roof on your home...rigid and no deforming. There a huge difference in lumber for a home up north vs a home down south, due to snow loads. There are ways to design screws that will bend, but won't fracture under a normal functional load. One design is what you see with the fastening screw for a Straumann Bone Level implant. There is the head with a bevel seat, then a long unthreaded shaft, and then the threaded portion. The bending movements are designed to happen in the unthreaded shaft. There is a point when the load exceeds the tensile strength of the alloy and it deforms. When that happens the unit has been stretched and it becomes loose. The worse outcome is it fractures. Most screws are designed to have a fracture point generally just below the head, so if there is an overload the broken portion can be removed and replaced. For the subject of common sense....common sense told the citizens of Salem, Ma that there were some "ladies" in their town that should be burned at the stake...so what we might think as common sense is not always true. Take a look at a jumbo jet and watch them load it with freight... common sense tells me that there is no way that thing should be able to fly. How can a sailboat sail into the wind?? Well time to go out and get the boat clean for the weekend....I may re tighten all the screws and bolts the more I think about it, Have a great Memorial Day and HI to Chris...nice to see you here [/QUOTE]
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