Strength and weight of materials

In summary, the block with a cross section of 2"x2" has a tensile strength of 8x greater than the block with a cross section of 1"x1".
  • #1
Dotini
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I have a basic question concerning strength and weight of materials. Please forgive me if my question is extraordinarily naive, but I'm an elderly retiree and my education is woefully lacking in this area. Thank you for your patience and understanding.

Let us say we have a block of X material with dimensions 1 x 1 x 1. So it has a cross section of 1 and a volume of 1.

Now, from the same base material, we produce a block with dimensions 2 x 2 x 2. It has a cross section of 4 and a volume of 8.

Would it be correct to say block #2 has a tensile strength 4x greater than block #1, and a weight 8x greater than block #1?

Is there some general rule that states that as an object is scaled up, its weight rises more steeply than its strength?
 
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  • #2
No, strength doesn't change. It is a material property independent on geometry. Strength is measured as force per unit area. What changes when you increase the cross section is the force necessary to break the material, not its strength. Strength to force is like density to weight. When we say that certain material is heavy or light weight we mean its density, i.e. weight per unit volume, not just its weight.
 
  • #3
Let's say you have a piece of Aluminum 6061-T6, with cross section 1" x 1" (length does not matter). This alloy has a tensile (yield) strength of about 40,000 psi. This means you'd need to tie one end vertically to a rigid beam, and hang 40,000 pounds on the other end to barely deform this metal (yield strength is generally a +0.2% stretch point). If your cross section is 2" x 2", you would need 160,000 lbs. to do the same thing. The ultimate strength is always at or above the yield strength, and for this alloy is approx. 45,000 psi. This means you would need 45,000 pounds to actually break the 1"x1" bar. Note also that between applying the yield strength and the ultimate strength, the metal will neck down, reducing the effective area under stress, leading to a more rapid break.

http://www.matweb.com/search/DataSheet.aspx?MatGUID=1b8c06d0ca7c456694c7777d9e10be5b&ckck=1

Compression strengths are generally close to tensile strengths in metals (but very different in say, concrete, where compression strength is high, but tensile is very low (thats why we add rebar)), but the actual usable compression strengths are also based on the geometry (length, solid .vs. pipe or tube, etc.), as the piece can buckle at a lower force than if you used a very short piece of material.
 

1. What is the difference between strength and weight of materials?

Strength refers to the ability of a material to withstand stress and resist deformation or breaking. Weight, on the other hand, is the measure of how heavy an object is due to the gravitational force acting on it. In other words, strength is a measure of the internal properties of a material, while weight is an external force acting on the material.

2. How is the strength of a material measured?

The strength of a material is typically measured using various tests such as tension, compression, shear, and bending tests. These tests apply force or stress to a material and measure its response, such as how much it can stretch or deform before breaking. The results of these tests are used to determine the material's strength properties.

3. What factors affect the strength and weight of materials?

The strength and weight of materials are influenced by several factors, including the type and composition of the material, its manufacturing process, and any external factors, such as temperature or humidity. The shape and size of the material also play a role in its strength and weight.

4. Why is it important to consider the strength and weight of materials?

The strength and weight of materials are crucial factors to consider in engineering and construction. Choosing the right materials with the appropriate strength properties ensures that structures and products are safe and can withstand the forces and stresses they will experience. Additionally, considering the weight of materials can help optimize designs and reduce costs.

5. Can the strength and weight of materials be improved?

Yes, the strength and weight of materials can be improved through various methods such as changing the material's composition or using different manufacturing techniques. For example, adding reinforcing materials or altering the structure of a material can increase its strength while reducing its weight. Ongoing research and advancements in technology also contribute to the development of stronger and lighter materials.

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