Notes, abstracts, papers, exams and problems of Technology

Testing Properties of Materials

Conformation

Used to know the degree of suitability of materials to manufacture parts.

Features

Used to know the mechanical characteristics of metal.

Understanding the Mechanical Properties of Materials

Used to find out the mechanical properties of materials.

Defects

Used to verify that there are no defects in the parts.

Mechanical Properties

• Hardness
• Tensile strength
• Yield strength
• and so on

Types of Hardness Measurements

• Scratch
• Penetration
• Rebound

Penetration Methods

• Brinell: A steel ball is used as the indenter, and the measurement is the area that the steel ball leaves.
• Rockwell: A diamond-tipped conical tip is used for hard materials, and a spherical tip is used for soft materials. Hardness is found by measuring the depth

Critical Path Method (CPM) and Program Evaluation and Review Technique (PERT)

Activity Duration and Delays

If an activity's slack (MTIJ) equals zero, any delay in this activity will delay subsequent activities. However, activities can not delay the project if MTIJ is greater than zero.

Critical Path

The critical path is the longest path, which represents the minimum time necessary to complete the project. Activities on the critical path are called critical activities.

Activities with Uncertain Duration

When the duration of activities is not known with certainty, three estimates are used: optimistic (a_ij), realistic (m_ij), and pessimistic (b_ij). It is assumed that the duration of activities follows a beta distribution. Assuming t_ij are independent... Continue reading "Project Management & Optimization: CPM, PERT, Network Flow, & Integer Programming" »

Piston Verification: Ensuring Optimal Engine Performance

Checking Piston Sliding Zones

Inspect the sliding zones of the piston. There should be no signs of jamming or excessive friction.

Weight Difference Between Pistons

Use a balance to compare the weight of each piston. Differences up to 4 grams are allowed. Larger differences can cause crankshaft imbalance and vibrations.

Piston Diameter

Pistons are not perfectly cylindrical. Follow the manufacturer's instructions to measure the diameter at the specified zone, usually at a certain distance from the head, measured transversally at the same height as the bolt. The installation clearance between the piston and cylinder compensates for thermal expansion and is typically between 0.02 and 0.05 mm.

Bolt

Data Encapsulation and Abstraction

Data encapsulation hides data from users, making it accessible only through class methods. This promotes abstraction, allowing users to utilize functionalities without needing to understand their internal workings.

Method Classification

Methods can be categorized into three groups:

• Constructors/Destructors: Initialize and finalize objects.
• Modifiers: Change data member values.
• Inspectors: Return object state information without altering it.

Friend Functions

Friend functions bridge the gap between unrelated functions and classes, enabling external access to private data members when necessary.

Inline Functions

Inline functions replace function calls with their code, offering advantages like method and friend compatibility,... Continue reading "Data Encapsulation and Abstraction in Object-Oriented Programming" »

Casting Processes

Casting: The process used to produce useful parts or objects from molten metal. It consists of pouring molten metal into a container (mold) shaped like the part or object being constructed, allowing it to harden as it cools.

Molds (e.g., sand, plaster, cavity wax, plastic) are filled with molten metal to produce parts similar to the mold shape.

Mold Types

• Green sand
• Dry layer
• Dry sand
• Metal
• Clay
• Furans
• CO2 process
• Special types

Foundry Core Characteristics

Cores must possess the following characteristics:

• Permeable
• Heat resistant
• Easy to collapse (after casting)
• Dry strength
• Friability
• Minimum tendency to generate gas

Pattern Types

Disposable Patterns

These are destroyed during the process of preparing the piece. They do not require special tolerances,... Continue reading "Metal Casting, Pressing & Machining Processes" »

4x4, AWD, and Transfer Case Systems

Limited Slip Differential

A limited-slip differential incorporates a mechanism to mitigate the standard differential's effect during situations where one wheel loses traction. This system engages automatically without driver intervention, unlike manual lockers.

Track-Lok

The Track-Lok system is a regular differential without locking. If one wheel rotates, the opposite wheel will generate the same torque. Part of the torque transmission from the crown gear is passed through a clutch. The clutch sets contain multiple clutch discs with radial grooves on plates made of fiber material.

Track-Lok clutches are engaged by two concurrent forces. The first is the preset force exerted by Belleville spring washers within... Continue reading "4x4, AWD, and Transfer Case Systems in Vehicles" »

Classifying Intermittent Injection Systems

Sequential: Fuel injectors provide fuel in a synchronized manner when the valve is open.

Semisecuencial: Fuel injectors trigger in couples every turn of the motor.

Simultaneous: Fuel injectors provide fuel at all times.

Accumulator Functions in NMEC Fuel Injection System

The accumulator keeps fuel pressure in the circuit after the engine stops, and it dampens the noise produced by the fuel pump.

Difference between Injection and Sequential Semisecuencial

The sequential injection fuel injectors provide fuel in a synchronized manner when the intake valve is open. The injection nozzles are driven by semisecuencial couples every turn of the motor.

No Combined Injections System

The combined injection systems are... Continue reading "Fuel Injection Systems: Operation and Functionality" »

What is Computer Security?

Security is the set of actions, tools, and devices whose purpose is to provide a computer system with integrity, confidentiality, and availability.

• Integrity: Prevents the modification of information by any user who has not been previously authorized.
• Confidentiality: Prevents data visualization by users who have no privileges on the system.
• Availability: Ensures that authorized users have access to the system and its resources when needed.

What Must We Protect Against?

We must protect against ourselves, accidents, breakdowns, malicious intruders, and malware.

Active Security

Active security is designed to prevent damage to computer systems:

1. Appropriate passwords
2. Data encryption
3. Computer security software

Passive Security

Passive

Character Devices and Block Devices

Character devices read and write data as a byte stream. Examples of character devices are printers and keyboards that allow the handling of a single byte at a time.

Block devices read and write information in fragments ("blocks") to the block device at a time. Examples include hard drives, floppy disks, and CD/ROM drives.

Locate Command

The locate command writes the names of files and directories that match a given pattern. It is the fastest of the two commands because it depends on a database (updated daily by default) instead of looking in real-time. It finds files that have been deleted since the last update of the database.

bzip2 Command

The bzip2 command tends to generate more compact compressed files but... Continue reading "Character & Block Devices, bzip2, Inodes, Links, Find & Mount" »

Hydraulic Systems

Storage

Fluid storage tanks are constructed of steel plates and brackets to contain fluid, sediment, and contaminants, and to dissipate generated heat. These tanks are typically coated with water-resistant paint. The bottom of the tank should be sloped with a drain plug for vacuum cleaning. Lids, vents, and air filters prevent the entry of impurities. Baffles within the tank prevent turbulent flow, allowing sediment to settle, separating air from the fluid, preventing foaming, and dissipating heat. Tank capacity should be 2-3 times the pump supply group capacity. Tanks should also have a sight glass, suction line, return line, and drainage.

Filtration

Filtration is the mechanical or physical process of separating materials using... Continue reading "Hydraulic Systems: Components, Functionality, and Maintenance" »