Have you ever wondered how we describe the properties of different materials? In this article, we will unlock the mysteries behind material properties and the words we use to describe them. Understanding these concepts will enhance your comprehension of future videos and enable you to decipher why certain materials are used in specific applications.
Contents
The Key Words of Material Description
To effectively characterize materials, we rely on six essential words: stiff, strong, ductile, brittle, tough, and hard. These words serve as a language that allows us to describe and analyze various materials. Armed with this vocabulary, you can gain insight into the properties of materials and their suitability for different purposes.
Delving Into Tensile Testing
First, let’s familiarize ourselves with a fundamental test called tensile testing. By subjecting a material sample to forces that gradually pull it apart, we can measure the resultant force and displacement. This test yields a stress/strain curve, providing valuable information about the material’s behavior under tension.
In this context, stress refers to the force applied to the test sample divided by its cross-sectional area. This measurement is expressed in Newtons per square meter, also known as Pascals. The stress is plotted on the y-axis of the stress/strain graph. On the other hand, strain describes the extent of deformation that occurs due to the applied force. It is determined by dividing the change in length by the original length and is represented on the x-axis.
Unveiling the Stress/Strain Graph
Let’s closely examine the stress/strain graph and decipher its meanings. As stress increases, the material begins to deform. This initial linear region is referred to as elastic deformation. If we remove the force, the material will regain its original shape, just like a rubber band. However, beyond the yield point, additional stress leads to permanent deformation, known as plastic deformation.
The stress continues to rise until it reaches the ultimate tensile strength point, which represents the maximum stress the material can endure. At this stage, the material’s cross section starts to decrease, a phenomenon referred to as necking. Finally, the material fractures under the stress.
Extracting Valuable Insights from the Graph
The stress/strain graph provides us with valuable insights. For instance, Young’s Modulus, also known as the elastic modulus, describes the stiffness of a material. It is determined by calculating the slope of the linear region in the graph. A steeper slope indicates a stiffer material, while a more gentle slope is indicative of flexibility. This property is widely used in engineering to predict deflection in various scenarios.
Yield strength and ultimate tensile strength are two other crucial properties. Engineers use these values, divided by a safety factor, to determine the maximum allowable stress for designing a product. While the aim is to keep the maximum stress well below failure, the safety factors may vary depending on the industry.
Exploring Different Material Types
Now, let’s explore different material types. A stiff material, as the name suggests, possesses high stiffness or Young’s Modulus. Consider a high carbon steel, which exhibits a steep slope on the stress/strain graph. In contrast, a flexible material, such as rubber, demonstrates a low Young’s Modulus, resulting in a more gradual slope.
Moving on, there are materials that fall between the extremes of stiffness and flexibility. These materials can be described as tough and ductile. “Tough” signifies the ability of a material to absorb a significant amount of energy without breaking, a property denoted by the area under the graph. On the other hand, “ductile” indicates the material’s capacity to deform under pressure.
The Dichotomy of Ductility and Brittleness
Materials can be classified as ductile or brittle based on their behavior under stress. Ductile materials, like the ones mentioned earlier, exhibit a characteristic cup and cone fracture surface when they break. In contrast, brittle materials, such as glass, ceramics, and cast iron, break with minimal deformation, resulting in granular flat fracture surfaces.
It’s interesting to note that some materials transition from ductility to brittleness as their temperature decreases. This phenomenon presented a significant challenge during World War II with the ill-fated Liberty ships. Several of these ships unexpectedly broke in half, including the SS John P. Gaines, in the frigid waters of the Bering Sea. It was discovered that the grade of steel used in their construction became brittle at lower temperatures. Stress concentration at the hatches further exacerbated the problem, as you learned in my previous video “Why Are Plane Windows Round?” This embrittlement may have also contributed to the fracture of the Titanic’s hull.
The Enigma of Hardness
Lastly, let’s delve into the concept of hardness, which is directly related to a material’s stiffness and yield strength. Hardness describes a material’s resistance to denting, scratching, and abrasion. The Rockwell hardness test is commonly used to measure this property. The test involves applying a minor load to establish a zero point, followed by the application of a major load to indent the material. The difference in depth between these two steps determines the material’s hardness.
For instance, diamond, known for its exceptional hardness, is utilized in cutting tools. Additionally, steel can be heat-treated to achieve tailored hardness. This approach is employed in swordmaking, where the cutting edge requires hardness, while the core of the blade needs to be ductile, allowing it to resist breaking under pressure.
Unlocking a World of Knowledge
We’ve now unveiled the secrets of material properties, providing you with a deeper understanding of the language and concepts used in the field of materials science and engineering. Armed with this knowledge, you can embark on a journey of exploration and gain insight into the countless applications and uses of different materials.
If you’re hungry for more tech-related information, head over to Techal for the latest insights and updates. Remember, knowledge is power, and the world of technology is filled with endless possibilities.
Thank you for joining us on this fascinating journey. Without sponsors like Lumerit, we wouldn’t have the opportunity to share these juicy secrets with you. Lumerit offers an innovative way to pursue higher education affordably and efficiently. Whether you’re aspiring to go to college or already enrolled, Lumerit can help you complete up to three years of college for a fraction of the cost. Take control of your education and explore how much you can save with Lumerit Scholar. Sign up today and embark on a path towards a brighter future.
