Chapter 1: Mechanical Properties of Materials

Chapter 1: Mechanical Properties of Materials

• Materials are physical substances used to make things.
• Knowledge of materials allows for comparison of everyday items (e.g., wood, metal, paper).
• Material properties include hardness, strength, flexibility, and magnetic behavior.
• These properties are related to everyday uses of the materials.
• Materials are crucial in engineering design and analysis.
• A wide variety of materials are available for diverse applications (aerospace to household).
• Material selection considers characteristics, specific application needs, advantages, and limitations.

I. Materials

• GLARE® is used in upper fuselage.
• Advanced cabin materials are used.
• CFRP rear pressure bulkhead is made of CFRP.
• CFRP vertical tail plane is constructed with CFRP.
• CFRP horizontal tail plane is made of CFRP.
• CFRP outer flaps and j-nose are made from CFRP.
• LBW (lower fuselage) and floor beams for upper deck are made of CFRP.
• CFRP center wing box components, including wing ribs and new alloys, are used.

Materials Families

• Materials are broadly classified into metals, polymers, ceramics, and composites.
• Metals can be further categorized into non-ferrous (e.g., aluminum, brass, copper, magnesium) and ferrous (e.g., cast iron, carbon steel, alloy steel, stainless steel)
• Polymers include thermoplastics, thermosets, and elastomers.
• Ceramics are generally oxides, nitrides, carbides, and sometimes, glasses or related compounds.
• Composites are combinations of two or more materials like a matrix and reinforcement.

Composites

• Composite materials are engineered from two or more constituent materials that remain separate while forming one component.
• One material usually forms the matrix and the other is the reinforcement.
• The materials must be chemically inert, unless a targeted degree of reaction is desired at the interface for bonding and strength.
• Typical applications include aerospace applications such as aircraft components.

Advantages/Disadvantages of Composites

• Advantages:
  • Light weight and low density
  • High creep resistance
  • High strength-to-weight ratio
  • Fatigue resistance
  • Ease of fabrication
  • High resistance to impact damage
  • Improved corrosion resistance
• Disadvantages:
  • High cost of raw materials and fabrication
  • Composites are brittle and easily damaged (especially transversely)
  • Weak matrix, low toughness
  • Difficult to reuse and dispose of
  • Difficulty in attachment
  • Difficulty with analysis
  • Cost fluctuation

Examples of Disadvantages

• Debonding within sandwich structure can lead to component failure (e.g., America's Cup boat).
• Damage to base of aircraft tail can lead to catastrophic failure (e.g., American Airlines Flight 587).

Composites/Boeing

• Increasing use of composites in newer Boeing aircraft models (e.g., 787) and the Airbus A380.
• Composite material percentages vary for different aircraft models.

Metals vs Composites

• Data demonstrating the continuous increase of composite materials in Airbus and Boeing aircraft over the years.

Distribution of Materials: Boeing 787

• Pie chart showing distribution of materials (e.g., carbon laminate, other composites) in the Boeing 787.

Airbus A380

• 25% of the Airbus A380 is composed of composites.
• Specific components like the rear pressure bulkhead, CFRP sections, floor beams, wing ribs, and flap tracks are identified.

Materials are classified

• Airbus A350: Materials are mostly composites (52%).
• Other material types and portions are identified (e.g. titanium, aluminum, steel, etc).
• The materials used in the design and construction of the Airbus A350 are discussed.

Metallurgical Materials & Components (Rafale)

• Dassault Rafale: Composite materials are frequently used to reduce weight.

II. Properties of Materials

• Various properties are outlined in detail based on the type of material (e.g., GLARE® in upper fuselage, advanced cabin materials, CFRP, KBE design, etc)

Introduction

• Material application depends on a thorough understanding of specific properties across different conditions.
• Property defines a quantitative/qualitative measurement of how/how much a material reacts to applied influences like force and temperature.
• A large variety of properties exists in materials.
• Mechanical properties determine how materials react to applied forces.
• Mechanical properties are frequently related to the elastic/plastic behavior of a material.
• Mechanical properties are expressed as a relation of stress and strain.
• Knowledge of mechanical properties lets one predict behavior under load.

Classification of Material Properties

• Physical properties: Density, Optical Properties, Conductivity (Acoustical - sound transmission/absorption)
• Mechanical properties: Strength, Toughness, Stiffness, Elasticity, Plasticity, Ductility, Brittleness, and Hardness.
• Electrochemical properties: Corrosion, Coating, and Wheat Phenomena
• Technological properties: Extractive, Metal Forming, Welding, Powder Metallurgy, Machining, Casting

Property of Material

• Property refers to a material's defining characteristics and their implications in various functions
• Examples include stress, strain, stiffness, ductility, elastic/plastic deformation, and toughness

Stress

• Tensile stress (σ) is calculated as force (F) divided by the original cross-sectional area (Ao) before loading.
• Shear stress (τ) is calculated as the force (Fs) applied parallel to a material's surface area (Ao)
• Stress is measured in N/mm² or MPa

Strain

• Strain (ε) is the amount of deformation per unit length.
• Tensile strain (ε) – change in length (Δl) divided by the initial length (l0).
• Lateral strain - change in width relative to the initial width.
• Shear strain– change in angle (Y) and is usually associated with a tangential force or torque and a perpendicular (normal) displacement.

Stress and Strain

• Relationships between stress and strain, true stress, true strain, engineering stress, engineering strain are discussed
• The relationship between these quantities with various charts and diagrams is included.

Stiffness

• Stiffness is the resistance of a material to elastic deformation
• Hooke's law states that within the elastic region, stress is proportional to strain (σ= Εε).

Design/Safety Factors

• Design uncertainties are considered to ensure the materials are safe.
• Factors of safety (N) are used to define the maximum stress to material failure.

Exercises

• Several example problems are included for working through and practicing various mechanical properties, stress, strain, etc.

Malleability

• Malleability is the ability of a material to be flattened into thin sheets without cracking (through cold or hot working).
• Malleability is a compressive property while ductility is a tensile property

Resilience

• Resilience is the capacity of a material to absorb energy elastically.
• The maximum energy stored up to the elastic limit is termed proof resilience.
• Proof resilience per unit volume is modulus of resilience.

Hardness

• Hardness is a material's resistance to scratching, abrasion, cutting, and penetration.
• Hardness methods are employed to determine a material’s hardness (Brine, Rockwell, Vickers)

Brittleness

• Brittleness is the property of breaking without much distortion.
• Materials can exhibit ductile or brittle behavior depending on temperature.

Creep

• Creep describes the gradual, progressive deformation of a material over time at a constant stress.
• Creep is primarily a high-temperature phenomenon and occurs even at loads below the material's elastic limit.

Fatigue

• Fatigue is the progressive, gradual crack growth in a material from an applied fluctuating or repeated stress.

Toughness

• Toughness is the amount of energy required to break a set unit volume of material.
• It is often calculated by the area under the stress-strain curve

Material Selection

• Material selection considers performance targets (e.g., cost, stiffness, weight, strength)
• Material Selection charts and graphs are useful to narrow down the options.
• The diagrams and charts are particularly effective in visualizing competing materials

Using Material Selection Charts

• Materials of a same material class (e.g., metals, etc) are clustered together.
• Charts can be used to easily distinguish between materials based on criteria (e.g., high strength, high stiffness, density).

Material Properties Used in Automotive Body Components

• Different material types are commonly used for various components.
• Pie charts and graphs demonstrate the use of mild steel, high strength steel, ultra-high steel, hot-formed steel, aluminum, etc.
• Properties relate to elongation, strength, and their implications for various performance.

References

• A list of cited sources is provided for further research and understanding in this subject matter.

Explore the fundamental mechanical properties of materials, from their physical characteristics to their applications in engineering design. This quiz delves into various materials like wood, metal, and composites, discussing their unique properties and usage in real-world contexts. Understand how materials impact the functionality of products across different industries.