AME Unit 4 Q1

Tensile stress is the force per unit area that tends to stretch a material. Imagine pulling on a rubber band; the force you apply is creating tensile stress in the rubber band.  

1. Tensile Stress: Definition, Formula, Unit, Calculation, and Examples | Xometry

Key Points:

• Force: The pulling force applied to the material.   1. Tensile Stress – Definition, Formula, Example, Unit, Meaning – BYJU’S byjus.com
• Area: The cross-sectional area of the material perpendicular to the force.   1. How does the cross-sectional area of an object affect stress?
• Stress: The ratio of the force to the area.   1. Tensile Stress: Definition, Formula, Unit, Calculation, and Examples | Xometry

Formula:

Tensile stress (σ) = Force (F) / Area (A)  

Units:

• Force: Newtons (N)
• Area: square meters (m²)
• Tensile stress: Pascals (Pa) or N/m²  

Visual Representation:

In essence, tensile stress is a measure of how much a material is being pulled apart.  

1. What is a Tensile Stress? Definition, Tensile Properties, Expression

Tensile stress is a fundamental concept in engineering, and it’s encountered in a wide range of applications. Here are some common examples:  

1. Is Tensile Stress or Strain? – Technische veren specialist – Tevema.com

Structural Engineering

• Bridges and buildings: The structural members, like beams, columns, and cables, experience tensile stress due to loads like weight, wind, and earthquakes.
• Suspension bridges: The main cables are subjected to significant tensile stress due to the weight of the bridge deck and traffic.   1. Objective Question with Answer for Cables and Frames – Download Free PDF – Testbook

Mechanical Engineering

• Pressure vessels: The walls of pressure vessels, such as boilers and tanks, experience tensile stress due to the internal pressure.   1. Stress Analysis of Thin-Walled Pressure Vessels – Scientific Research Publishing www.scirp.org
• Machine components: Parts like shafts, axles, and bolts undergo tensile stress during operation.
• Material testing: Tensile tests are conducted to determine the mechanical properties of materials, including tensile strength, yield strength, and ductility.   1. Tensile Test – STEP Lab step-lab.com

Other Engineering Fields

• Aerospace engineering: Aircraft components like wings and fuselage experience tensile stress during flight.   1. Introduction to Aerospace Flight Vehicles – Eagle Pubs eaglepubs.erau.edu
• Civil engineering: Anchor bolts and rebar in concrete structures are subjected to tensile forces.

Essentially, any engineering application involving pulling forces will involve tensile stress.

Marine environments present a unique set of challenges due to factors like saltwater corrosion, wave action, and extreme pressures. Tensile stress is a critical consideration in designing structures and equipment for these conditions.  

1. Marine Grade Fasteners Challenges On The Water – Metric Bolt

Here are some examples:

Shipbuilding and Offshore Structures

• Hull structures: The hull of a ship or offshore platform experiences tensile stress due to wave forces and internal pressures.
• Mooring systems: Chains and cables used for mooring vessels must withstand significant tensile loads due to wave action and wind.
• Subsea pipelines: These pipelines are subject to tensile forces from internal pressure, wave action, and ocean currents.

Marine Equipment

• Anchors: The anchor shank experiences tensile stress when holding a vessel in place.
• Fishing gear: Fishing lines and nets are subjected to tensile forces when hauling in catches.
• Oceanographic equipment: Instruments deployed in the ocean, such as buoys and underwater sensors, must be designed to withstand tensile loads from water currents and wave action.

Marine Renewable Energy

• Offshore wind turbines: The tower and foundation of an offshore wind turbine experience tensile stresses due to wind loads and wave forces.
• Ocean wave energy converters: The components of these devices are subjected to tensile stresses from the wave energy.

In essence, any marine structure or equipment that is subjected to pulling forces will experience tensile stress.

Shear stress is the force per unit area acting parallel to the surface of a material. Imagine trying to cut a piece of paper with scissors; the force you apply to the blades creates shear stress on the paper.  

1. Mechanics of Materials: Stress » Mechanics of Slender Structures | Boston University

Key Points:

• Force: The force applied parallel to the material’s surface.   1. Shear Stress: Definition, How it Works, Example, and Advantages – Xometry www.xometry.com
• Area: The area of the surface being acted upon.
• Stress: The ratio of the force to the area.

Formula:

Shear stress (τ) = Force (F) / Area (A)  

1. Shear Stress: Definition, How it Works, Example, and Advantages – Xometry

Units:

• Force: Newtons (N)
• Area: square meters (m²)   1. Shearing Stress – Definition, Examples, Units, Formula, Meaning – BYJU’S byjus.com
• Shear stress: Pascals (Pa) or N/m²   1. Shear stress – Wikipedia en.wikipedia.org

Visual Representation:

Essentially, shear stress is a measure of how much a material resists deformation when two forces act in opposite directions across its surface.  

1. Shearing Stress – Definition, Examples, Units, Formula, Meaning – BYJU’S

Shear stress is prevalent in various engineering applications. Here are some common examples:  

1. Shear Stress: Meaning, Examples, Applications – StudySmarter

Structural Engineering

• Beams: When a beam is subjected to bending, internal shear stresses develop. These stresses are crucial for designing the beam’s cross-sectional dimensions to prevent failure.   1. Mechanics of Materials: Bending – Shear Stress – Boston University www.bu.edu
• Connections: Rivets, bolts, and welds are subjected to shear stress when they connect structural members.
• Retaining walls: The soil behind a retaining wall exerts shear stress on the wall, which must be considered in the design.

Mechanical Engineering

• Shafts: Shafts transmitting torque experience shear stresses due to the twisting action.   1. Relationship of torque and shaft size – Plant Engineering www.plantengineering.com
• Gears: Gear teeth are subjected to shear stresses during meshing.   1. Spur Gears Static and Dynamic Meshing Simulation and Tooth Stress Calculation www.researchgate.net
• Cutting tools: The cutting edge of tools like drills and milling cutters experiences shear stresses as they remove material.

Other Engineering Fields

• Aerospace engineering: Aircraft wings and fuselages encounter shear stresses due to aerodynamic forces.   1. Shear Stress Distribution in a Fuselage of an Aircraft – ResearchGate www.researchgate.net
• Civil engineering: Soil mechanics involves the study of shear stresses in soil, which is crucial for foundation design.   1. What Is the Shear Strength of Soil? Tests and Formula – Tensar www.tensar.co.uk

Essentially, any engineering application involving forces acting parallel to a surface will involve shear stress.

Shear Stress in Marine Engineering

Shear stress is a critical consideration in marine engineering, as it impacts the structural integrity and performance of various components. Here’s a breakdown of where it’s prevalent:

Ship Hull Structure

• Transverse and longitudinal bulkheads: These structures experience shear forces due to wave actions, cargo loading, and other external forces.
• Deck and bottom plating: Shear stresses occur due to bending moments and torsional loads.
• Frames and stiffeners: These structural members are subjected to shear forces in conjunction with bending and compressive stresses.

Propulsion Systems

• Shafts: Torque transmission induces shear stresses within the shaft material.   1. Mechanical properties of materials: Shafts in torsion – Linear Motion Tips www.linearmotiontips.com
• Propellers: The blades experience shear forces due to water resistance and thrust generation.
• Couplings: These components transmit torque, resulting in shear stresses.

Other Components

• Piping systems: Fluid flow and pressure fluctuations can induce shear stresses in pipes and fittings.
• Marine equipment: Components such as winches, cranes, and hydraulic systems are subject to shear stresses during operation.

Environmental Factors

• Wave and current forces: These forces exert shear stresses on the hull and other submerged structures.
• Ice loading: In regions with ice, ship hulls experience shear forces due to ice impact.

Understanding shear stress distribution is essential for ensuring the structural integrity and safety of marine vessels. Engineers use advanced analysis techniques, such as finite element analysis, to evaluate shear stress levels and optimize designs.environments, impacting processes from sediment transport to the behavior of marine life.

Compressive stress is the stress experienced by a material when it is subjected to forces that push inward, causing it to compress or shorten. Think of squeezing a sponge; you’re applying compressive stress to it.  

1. Compressive Stress: Definition, Unit, Formula, and Example | Xometry

Key points:

• Force: The pushing force applied to the material.   1. Compressive stress – Wikipedia en.wikipedia.org
• Area: The cross-sectional area of the material perpendicular to the force.   1. How does the cross-sectional area of an object affect stress? – TutorChase www.tutorchase.com
• Stress: The ratio of the force to the area.   1. Compressive Stress: Definition, Unit, Formula, and Example | Xometry www.xometry.com

Formula:

Compressive stress (σ) = Force (F) / Area (A)  

1. What is Compressive Stress? – Definition, Formula, Unit, Dimension – BYJU’S

Units:

• Force: Newtons (N)
• Area: square meters (m²)   1. Compressive Stress: Definition, Unit, Formula, and Example | Xometry www.xometry.com
• Compressive stress: Pascals (Pa) or N/m²   1. Compressive Stress: Definition, Unit, Formula, and Example | Xometry www.xometry.com

Note: To differentiate compressive stress from tensile stress (which is pulling), compressive stress is often represented with a negative sign

Compressive stress occurs when a material is subjected to forces that push inward, causing it to compress or shorten. Here are some common examples in engineering:  

1. Compressive Stress: Definition, Unit, Formula, and Example | Xometry

Structural Engineering

• Columns and pillars: These structures are designed to resist compressive loads from roofs, floors, and other structural elements.   1. 4 basic concepts when forming columns or pillars – Alsina.com www.alsina.com
• Foundations: Buildings, bridges, and other structures rely on foundations to distribute compressive loads to the ground.
• Dams and retaining walls: These structures withstand the compressive forces exerted by water or soil.
• Arch bridges and domes: These structures utilize compressive forces to maintain their shape.   1. Explore Tension and Compression | The Inka Empire – National Museum of the American Indian americanindian.si.edu

Mechanical Engineering

• Press-fit assemblies: Components are often pressed together, creating compressive forces between them.
• Hydraulic systems: Fluids exert compressive forces on the system components.
• Compression springs: These springs store energy by compressing.   1. Compression Spring Mechanism – How Does it Work? lesjoforssprings.com

Other Fields

Material science: Compression testing is used to determine the compressive strength of materials.   1. What is Compression Testing? – Instron www.instron.com

Geotechnical engineering: Soil and rock masses are subjected to compressive stresses due to overburden and other loads.

Compressive stress is a significant factor in marine engineering, especially when dealing with the immense pressures exerted by water. Here are some common examples:

Ship Hulls

• Submerged sections: The lower part of a ship’s hull experiences compressive stress due to the hydrostatic pressure of the water.
• Ice loading: Ships operating in icy waters must be designed to withstand compressive forces from ice impact.

Offshore Structures

• Subsea foundations: These structures are subjected to immense compressive forces from the overlying water column and seabed sediments.
• Concrete gravity platforms: The massive weight of these platforms creates compressive stresses in their concrete structures.

Marine Equipment

• Submersible pressure vessels: These vessels must withstand high compressive pressures at great depths.
• Hydraulic systems: Components in hydraulic systems experience compressive forces due to fluid pressure.

Other Applications

• Diving equipment: Scuba tanks and other equipment must be designed to resist compressive forces at depth.
• Oceanographic instruments: Instruments deployed at great depths experience high compressive pressures.

Understanding compressive stress is crucial for ensuring the safety and reliability of marine structures and equipment.

Several components in a diesel engine experience tensile stress during their operation. Here are some key examples:

Connecting Rod

• Upper half: This part is subjected to tensile stress during the power stroke as it pulls the piston upwards, converting the linear motion into rotational motion.

Piston

• Piston rings: While primarily under compressive stress, they can experience tensile stress due to thermal expansion and other factors.
• Piston crown: Although primarily under compressive stress, the piston crown can experience tensile stresses in specific areas due to bending and thermal gradients.

Crankshaft

• Fillet radii: These areas, where the crankshaft changes diameter, can experience tensile stresses due to bending moments.
• Journal and main bearing surfaces: While primarily under compressive stress, tensile stresses can occur due to bending and torsional loads.

Other Components

• Bolts and fasteners: These components are inherently designed to withstand tensile forces.
• Valve springs: When compressed, they store potential energy, which is essentially tensile stress.

It’s important to note that while these components primarily experience tensile stress, they are also subjected to other types of stress, such as compressive, shear, and torsional stress. The combination of these stresses determines the overall strength and durability of the engine components.

Shear stress occurs when forces act parallel to a material’s surface. In a diesel engine, several components experience this type of stress:  

Lubrication System

• Oil film: The lubricating oil film between moving components experiences shear stress as they move relative to each other. This determines the oil’s viscosity and its ability to protect the surfaces.
• Oil pump gears: These gears experience shear stress as they mesh and transmit power.

Internal Combustion Process

• Piston rings and cylinder walls: The friction between these components generates shear stress, affecting engine efficiency and wear.
• Valve train: The contact between the camshaft and pushrods, lifters, or rocker arms involves shear stresses.

Other Components

• Bearings: The oil film between the bearing surfaces experiences shear stress.
• Crankshaft: While primarily under compressive and bending stresses, there are also localized areas where shear stresses occur.
• Couplings: If used, flexible couplings transmit torque through shear stresses.

Understanding shear stress is crucial for optimizing engine performance, reducing wear, and extending component life.

Compressive stress occurs when a material is subjected to forces pushing inward. In a diesel engine, several components experience this:  

Piston and Cylinder Assembly

• Piston crown: The piston crown faces immense compressive forces during combustion due to the high pressure of the gases.
• Cylinder walls: The cylinder walls experience compressive stresses from the piston rings and the pressure of the combustion gases.
• Connecting rod bearings: These bearings are subjected to compressive loads from the crankshaft journal.

Crankshaft

• Main and connecting rod journals: These components experience compressive stresses from the bearing loads.
• Crankshaft webs: While they also experience bending and torsional stresses, they are subjected to compressive forces in certain areas.

Other Components

• Valve seats: These components withstand the compressive force exerted by the closing valve.
• Injection pump components: Certain components within the injection pump, such as plungers and barrels, experience compressive stresses during operation.

It’s crucial to understand these stress distributions to design engine components with sufficient strength and durability.

The cylinder head is the component in a 4-stroke diesel engine that has the maximum recommended service life due to constant cyclic stress.

It experiences extreme temperature variations and high pressures during each combustion cycle, leading to significant thermal and mechanical stresses.

These cyclic stresses can cause fatigue cracks and eventually lead to failure.

1. Engine cylinder head: functions and characteristics for high performance – ITR