Brittleness refers to a material’s tendency to fracture or shatter when subjected to stress or impact. A brittle substance has no elasticity and shows little deformation before shattering. Glass and ceramics are common examples of brittle materials. Brittle behavior occurs when atoms in a material are unable to glide past each other while retaining the overall integrity of the atomic lattice structure.
Brittleness is a quality in materials science that describes a material’s tendency to fracture with minimal plastic deformation. Brittle materials have a limited ability to absorb impact energy before fracture.
Brittle materials have limited tensile strength, poor impact resistance, and mild deformation. Furthermore, their compressive strength is high. Most inorganic and nonmetallic materials are brittle. Aside from hardness, several other factors influence brittleness. Crystal structure, bonding type, and microstructure are a few examples. Glass and other materials with an uneven or amorphous arrangement of atoms are particularly brittle. This is because, under stress, their atomic structure prevents considerable plastic deformation, which results in instantaneous fracture.
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Factors affecting brittleness
- When a material reaches its strength limit, it often has two options: deformation or fracture. A naturally malleable metal can be strengthened by inhibiting the mechanisms of plastic deformation; however, if this is done in excess, fracture occurs more frequently, and the material becomes brittle. As a result, precise balance is required to increase the materials’ toughness.
- A material’s crystal structure has a significant impact on its brittleness. Glass and other materials with an uneven or amorphous arrangement of atoms are particularly fragile. However, materials like metals that have an ordered atomic organization are typically more flexible and less brittle.
- The type of bonding in a material also influences its brittleness. Ceramics and other materials with mostly ionic or covalent bonding tend to be more brittle than those with metallic interactions. This is due to the fact that ionic and covalent bonds are stronger and less flexible, allowing the material to bend less before fracture.
- Microstructural flaws, including fractures, voids, and inclusions, can all contribute to brittleness. These flaws serve as stress concentrators, causing and propagating fractures. As a result, materials having a high density of flaws are more brittle.
- Pressure can often increase a material’s brittle strength. For example, this occurs in the brittle-ductile transition zone, which is found in the Earth’s crust at a depth of roughly 10 kilometers (6.2 miles), where rock is more likely to flex ductility and less likely to brittle.
Determination of Brittleness
Brittle materials are frequently chosen for designs due to their great strength. Brittle failure, however, can be disastrous since brittle materials can break suddenly and without much notice. So, it is critical to detect brittle materials since they can have an impact on the design’s success and durability.
Brittleness is measured by performing a tensile test and estimating the material’s ductility. Brittleness is defined as a material’s low ductility during a tensile test. The standard test technique for conducting tensile testing on metallic materials is ASTM E8.
Brittleness in different materials
- Polymer mechanical properties are sensitive to temperature variations near room temperature. For example, poly (methyl methacrylate) gets increasingly ductile as the temperature rises, after being highly brittle at 4°C.
- Some metals’ slip systems cause them to be brittle. The more slip systems a metal has, the less brittle it is since many of them can experience plastic deformation. However, with fewer slip systems, plastic deformation may be reduced, making the metal more brittle.
- Ceramics are frequently fragile due to the difficulties of dislocating or sliding. Because there are few slip systems in crystalline ceramics, deformation is complicated, and the ceramic becomes more brittle.
- Bronze, a copper-tin alloy, is usually ductile and malleable. However, high tin content might cause brittleness.
- Brittle materials include alloys with poor plasticity, such as cast iron or titanium. An alloy’s brittleness is strongly influenced by its crystal structure. Materials with an FCC structure, such as copper, are more ductile than HCP structures, such as titanium or magnesium.
- Dry plaster A colourless calcium sulphate mineral that is used with water for construction or modelling, although it becomes brittle as it loses water and hardens.
- Although steel is usually tough and ductile, high-carbon steel can become brittle due to its high carbon content.
Role of hardness in brittleness
- Materials with high hardness have reduced impact toughness, making them more prone to shatter from sudden or high-energy impacts. Their strength may be focused in specific locations, making them susceptible to fracture initiation.
- In general, tougher materials are less flexible, which means they deform less before breakage. This decreased ability to absorb energy via plastic deformation can lead to increased brittleness.
Brittle Fracture
A brittle fracture is an abrupt and rapid metallic failure in which the material exhibits minimal or no plastic strain. This is characterized by sudden collapse with no warning. The created cracks spread swiftly, and the material falls abruptly.
Brittle fracture is a condition that happens when a substance is exposed to temperatures that reduce its resilience, making it more brittle. The risk for brittleness varies depending on the type of material exposed to these low temperatures.
A brittle fracture in metal is caused by crack propagation across crystallographic planes and is often associated with minimal plastic deformation.
Types of brittle fracture
While there are several ways to classify brittle fractures, based on the breakage system there are two types i.e., transgranular and intergranular fractures.
Transgranular Fracture: This type of fracture, also known as trans crystalline fracture, penetrates the grains of a crystalline structure. Transgranular fracturing is typically more damaging since modest damage can lead to major structural failure because of the rapid fracture propagation across the grains.
Intergranular Fracture: In this fracture, Cracks spread along the grain boundaries of the material. On the contrary, an intergranular fracture occurs at a material’s grain boundaries. These fractures frequently reflect a material’s inherent weakness, such as contaminants near the grain boundaries or poor grain structure. They mostly damage the grain boundaries while leaving the material’s interior structure reasonably intact.
References
- https://www.sciencedirect.com/topics/chemistry/brittleness
- https://www.tevema.com/does-higher-hardness-mean-more-brittle/
- https://blog.thepipingmart.com/other/explain-in-detail-the-concept-of-brittleness/
- https://slideplayer.com/slide/7875269/
- https://www.studysmarter.co.uk/explanations/engineering/materials-engineering/brittle-fracture/
