Strength is one of the most important mechanical properties of a material and determines its ability to absorb energy before failure. It plays a key role in many technical solutions: from the manufacture of car bodies to the development of medical implants. This article examines in detail the concept of strength, its measurement methods, and practical applications.
Definition of flexibility
Strength is the amount of energy a material can absorb before breaking. It is measured in joules per cubic meter (J/m³) or megajoules per cubic meter (MJ/m³).
Key concepts:
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A measure of a material’s resistance to destruction.
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Combination of strength and flexibility
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Area under the stress-strain curve up to the point of failure
Calculation formula:
Stiffness = ∫ σ dε (strain from zero to failure)
a kind of stubbornness
1. Tensile strength
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Energy absorbed in tensile test
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Suitable for handling materials.
2. Impact resistance
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Energy absorption in impact tests
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Measured using the Charpy or Izod method
3. Fracture toughness
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Resistance to crack growth
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Determined by the parameter K₁₋.
Factors that influence sustainability
1. Structure of matter
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FCC metals generally have greater durability.
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Materials with HCP structure have lower stiffness.
2. Temperature
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Lowering the temperature usually reduces the hardness.
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Ductile-brittle transition temperature (DBTT) of some metals
3. Download speed
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Rapid loading usually reduces stiffness.
4. Microstructure
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granules
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Current status
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Precipitation distribution
Comparison of the hardness of different materials
Metal:
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Mild steel: 50–200 MJ/m³
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Aluminum 6061: 20-50 MJ/m³
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Pure titanium: 70-120 MJ/m³
Polymer:
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Polycarbonate: 30-80 MJ/m³
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Nylon 6: 50-150 MJ/m³
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Natural rubber: 100-500 MJ/m³
Composite materials:
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Carbon fiber/ epoxy resin : 50-150 MJ/m³
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Kevlar fibers: 30-100 MJ/m³
How to measure hardness
1. Tensile test
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Calculate the area under the stress-strain curve.
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ASTM E8 standard
2. Charpy impact test
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Measurement of the energy absorbed during a fault
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ASTM E23 standard
3. Fracture toughness test
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Determine K₁₋ in different ways
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ASTM E399 standard
The importance of flexibility in design
1. Security design
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Prediction of material behavior under dynamic loading
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Prevent sudden outages
2. Material selection
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Commitment to working conditions
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Improving profitability
3. Quality control
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Confirm the material specifications
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Detection of microstructural changes
4. Assessment of productive life
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Prediction of fatigue resistance
Relationship between hardness and other properties
1. Power
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High-strength materials typically have low stiffness.
2. Expansion
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Higher elongation usually results in higher stiffness.
3. Hardness
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Feedback relationships in many materials
4. Modulus of elasticity
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Materials with a high modulus of elasticity generally have lower stiffness.
Industrial application
1. Automotive industry
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Materials that absorb energy in accidents
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Design of security systems
2. Airspace
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The housing is made of shock-resistant material.
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Dynamically load-bearing components
3. Medicine
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High-strength implants
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Surgical instruments
4. Construction
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earthquake-resistant materials
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Bridges and critical structures
Opportunities to improve flexibility
1. Alloy
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Add suitable alloying elements.
2. Heat treatment
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Annealing to restore hardness
3. Modification of the microstructure
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Granule control
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Sedimentary flood management
4. Use of composite materials
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A mixture of plastic and hard materials.
Related standards
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ASTM E23: Charpy impact test
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ASTM E399: Fracture toughness
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ISO 12135: Determination of fracture toughness
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DIN 50115: Impact test
Finally
Toughness, a measure of a material’s resistance to damage , plays a key role in product design and development. A better understanding of this concept and the factors that influence it helps engineers select optimal materials and develop safer products. In the development of new materials, improving toughness remains a central goal of materials science.
Frequently Asked Questions
1. What is the difference between hardness and resistance?
Strength is the ability to resist deformation, and toughness is the ability to absorb energy before failure.
2. Why do some materials have high strength but low hardness?
Since they normally have very little elongation, they cannot absorb much energy.
3. How does temperature affect hardness?
In general, hardness decreases with decreasing temperature (except in some special cases).
4. Is high hardness always desirable?
No, it depends on the application. In some cases, we need a brittle material.
5. How can the strength of polymers be increased?
By changing the molecular structure, adding plasticizers or using strengthening agents.