JC Engineering flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hooke's law

Within the elastic range, stress is proportional to strain: σ = Eε, where E is Young's modulus. Beyond the proportional limit the relationship becomes nonlinear and permanent deformation may occur.

Reynolds number

Dimensionless ratio Re = ρvD/μ describing flow regime. Values below about 2000 indicate laminar flow, above about 4000 turbulent flow, and between them a transitional regime.

Factor of safety

Ratio of a material's failure strength to the allowable working stress. It accounts for load uncertainty, material variability and consequences of failure; below 1 predicts failure.

Goodman relation

Fatigue criterion combining alternating and mean stress: σa/Se + σm/Su = 1. It gives a conservative estimate of infinite-life safety for ductile materials under combined steady and cyclic loading.

Tolerance stack-up

Accumulation of individual part tolerances in an assembly. Worst-case analysis sums tolerances directly; statistical root-sum-square analysis predicts the probable variation and is less conservative.

Martensite formation

Hard, brittle phase formed when austenite cools too fast for diffusion, as in quenching. Tempering afterwards reduces brittleness and relieves internal stress while retaining useful hardness.

Heat-affected zone

Region of parent metal whose microstructure and properties are altered by welding heat without melting. It can harden or embrittle and often governs joint toughness and cracking risk.

Critical path

Longest duration sequence of dependent activities through a project network. It has zero total float, so any delay on it directly delays project completion.

Cost performance index

CPI = EV/AC, the ratio of earned value to actual cost. A value below 1 means work is costing more than budgeted; EAC is often forecast as BAC/CPI.

Schedule variance

SV = EV − PV, the difference between earned value and planned value. A negative value indicates the project is behind the planned schedule at the reporting date.

Process capability index

Cpk = min[(USL − μ), (μ − LSL)]/3σ. It measures whether a centred or off-centre process fits within specification limits; values of 1.33 or more are commonly required.

Control chart

Plot of a process measure over time with statistical control limits. Points outside the limits or non-random patterns signal special-cause variation requiring investigation.

Pareto analysis

Ranking causes of a problem by frequency or impact. It applies the principle that a small number of causes, roughly 20 percent, produce most of the effect.

Hierarchy of controls

Ranking of risk controls by effectiveness: elimination, substitution, engineering controls, administrative controls, then personal protective equipment as the least effective last resort.

Lockout tagout

Formal procedure isolating all energy sources, dissipating stored energy and verifying zero energy before maintenance. Each worker applies a personal lock so equipment cannot be re-energised.

Confined space entry

Entry into a space with limited access and possible hazardous atmosphere. Requires atmospheric testing, a permit, an attendant outside and rescue arrangements before entry.

Code versus standard

A code is a legally adopted set of rules; a standard is a consensus technical document. Codes frequently reference standards, which then become enforceable through adoption.

Order of precedence

Contractual ranking that resolves conflicting documents. Typically the specification and contract terms outrank general drawings, so the higher-ranked document governs the requirement.

Present worth factor

P = F/(1 + i)^n converts a future amount to today's value at interest rate i over n periods. It is the basis for comparing alternatives by net present value.

Internal rate of return

Discount rate at which a project's net present value equals zero. A project is economically acceptable when its IRR exceeds the required minimum attractive rate of return.

Capital recovery factor

Factor converting a present amount to an equivalent uniform annual payment: i(1 + i)^n/[(1 + i)^n − 1]. It is used for annual worth comparisons and loan payments.

Public safety paramount

Ethical principle placing protection of public health, safety and welfare above employer or client loyalty. Engineers must escalate unresolved safety concerns rather than stay silent.

Conflict of interest

Situation where personal or financial interest could improperly influence professional judgement. It must be disclosed promptly and, where material, the affected decision avoided.

Sealing documents

Affixing a professional seal certifies personal responsibility for the work. An engineer should seal only documents they prepared or directly supervised and reviewed.

Availability formula

Availability = MTBF/(MTBF + MTTR). It expresses the fraction of time equipment is operable; shortening repair time raises availability as effectively as improving reliability.

Bathtub curve

Failure-rate pattern over asset life: decreasing infant mortality, constant useful-life failures, then increasing wear-out failures. Maintenance strategy should differ for each region.

Overall equipment effectiveness

OEE = availability × performance × quality. It combines downtime, speed losses and defect losses into one measure; roughly 85 percent is considered world-class.

Series system reliability

System reliability equals the product of component reliabilities, so it is always lower than the least reliable component. Adding parallel redundancy is the usual way to raise it.

Earned value management

Method integrating scope, schedule and cost by comparing earned value with planned value and actual cost, yielding schedule and cost performance indices for forecasting.

Stress concentration factor

Kt is the ratio of peak local stress at a geometric discontinuity to nominal stress. It amplifies the alternating stress in fatigue assessment of notches, holes and fillets.

Corrosion allowance

Extra material thickness added to pressure equipment so that expected in-service corrosion does not reduce the wall below the minimum required thickness during design life.

Predictive maintenance

Condition-based maintenance triggered by measured indicators such as vibration, temperature or oil analysis. It schedules intervention before functional failure, reducing unplanned downtime.