Machine Design Exam 1 Reviewer

LECTURE 1:

TERMINOLOGIES

Mass

  • Defined as the amount of mattter in a body. It remains constant regardless of the bodys location on Earth or in space.

Inertia

  • Property of a body to resist changes in its state of motion or rest. Mass is the measure of:

Newtons 1st Law

  • A body remains at rest of in uniform motion unless acted upon by an external force.

Newtons 2nd Law

  • Newtons second law of motion states that the object will accelerate in the direction directly proportional to the unbalanced force acting on it.

Newtons 3rd Law

  • For every action, there is an equal and opposite reaction.

Weight

  • Defined as the force exerted by gravity on a body. Changes depending on the gravitational field. It is measured in Newtons (N)

Moment of Force

  • The rotational effect of a force about a point or axis

Couple

  • Two equal and opposite parallel forces whose lines of action are different.

Torque

  • The turning effect of a force

Energy

  • Is the capacity to perform work. It is a fundamental concept in physics and engineering, representing the ability of a system to cause change or do work, such as moving an object, generating heat, or producing light.

Work

  • is done when a force causes displacement

Power

  • Rate of doing work

Load - is any external force acting upon a machine part. It influences the design and durabilty of the part. Different types of loads affect materials and components in unique ways

  • Dead or Steady Load - a constant force that does not change in magnitude or direction.

  • Live or Variable Load - a force that changes continously.

  • Shock Load - is a sudden force or load applied to a system, often causing a rapid change in motion or stress. It occures over a short period of time but is not necessarily instantaneous .

  • Impact Load - is a force exerted by a moving object when nit collides with another object or surface in a very short duration, oftern producing a high peak force. Occurs instantly upon contact.

Strength of materials - is a measurement of the materials ability to resist or withstand forces that result from stress and strain.

Stress - stress represents the internal resistance of a material to deformation under and external load. Changes in stress occur because the material adjusts to varying force and area conditions. If stress exceeds the materials strength, deformation, or failure can occure

Relationship between Stress and Strength:

  • stress tells you how much force per unit area is acting on a material at a given moment

  • strength defines the limits of stress the material can withstand without failure

Types of Stress:

  1. Tensile Stress - Occurs when a material is subjected to a force that pulls it apart.

  2. Compressive stress - Results from a force that compresses or squeezes the material.

  3. Shearing stress - Occurs when a force causes layers of the material to slide against each other.

  4. Bearing stress - The contact pressure between two surfaces. Bearing stress, also referred to as crushing stress, is a localized compressive stress that occurs at the surface of contact betwen two machine parts that are in relative motion or are stationary under a load. It typically appears in areas where one component presses against another, such as in riveted joints, cotter joints, or journal bearings.

  5. Torsional stress - Associated with twisting, it occurs when torque is applied around the shaft axis.

  6. Flexural or Bending stress - Occurs when a material is subjected to bending forces, often relevant in beams and other structural components

  7. Combined stress - Situations where different types of stress act simultaneously on a material, necessitating combined stress analysis.