PEP key terms

A multiplier that expresses how much local stress at a geometric discontinuity, such as a hole or fillet, exceeds the nominal stress computed on the unmodified cross section.

A fracture-mechanics quantity describing the magnitude of the stress field near a crack tip, compared against a material's fracture toughness to judge whether a crack will propagate.

A material property measuring resistance to crack extension under opening-mode loading, used with applied stress intensity to assess the safety of a cracked component.

The stress amplitude below which a material can endure an effectively unlimited number of load cycles without failure, characteristic of steels but absent in many aluminum alloys.

A plot of cyclic stress amplitude against the number of cycles to failure, used to estimate fatigue life at a given alternating stress level.

A linear failure criterion relating mean stress and alternating stress, letting an engineer adjust an allowable stress amplitude for the presence of a nonzero mean load.

The ratio of a component's capacity or strength to the load or stress it is expected to experience, providing margin against uncertainty in loads, material properties, and analysis.

A design method that checks factored load combinations against factored resistance for each defined failure condition, such as strength, serviceability, and stability.

A probability-calibrated design format in which nominal loads are multiplied by load factors and nominal resistances by resistance factors so that factored demand does not exceed factored capacity.

A design approach in which computed service-level stresses are kept below a material's allowable stress, obtained by dividing a strength or yield value by a safety factor.

A graphical construction that transforms stress or strain components between coordinate orientations, giving principal values and maximum shear from a state of plane stress or strain.

A normal stress acting on a plane where shear stress is zero; the largest and smallest principal stresses bound the stress state and drive many failure criteria.

An equivalent stress combining the deviatoric components of a three-dimensional stress state, compared with yield strength to predict yielding of ductile metals.

A plot of applied stress versus resulting strain for a material, revealing elastic modulus, yield point, ultimate strength, and ductility.

The slope of the linear elastic portion of a stress-strain curve, quantifying a material's stiffness and its resistance to elastic deformation under axial load.

The negative ratio of transverse strain to axial strain in a uniaxially loaded material, typically near 0.3 for metals and used in multiaxial and volumetric analyses.

The stress at which a material begins to deform plastically, often reported as a 0.2 percent offset value for metals lacking a distinct yield point.

The fractional change in length per unit temperature change, used to compute thermal strains and the stresses induced when expansion is restrained.

Time-dependent permanent deformation of a material under sustained stress, significant at elevated temperatures and evaluated against allowable deformation over a design life.

Sudden loss of stability of a slender member under compressive load, occurring at a critical load that depends on end conditions, stiffness, and unsupported length.

The theoretical axial compressive load at which an ideal elastic column becomes unstable, proportional to the product of elastic modulus and moment of inertia and inversely proportional to effective length squared.

Effective length divided by the least radius of gyration of a compression member, indicating whether buckling or yielding governs its strength.

Graphical plots of internal shear force and bending moment along a beam, used to locate maximum values and select cross sections.

The ratio of a cross section's moment of inertia to its distance from the neutral axis to the extreme fiber, used to convert bending moment into maximum bending stress.

The displacement of a structural member under load, typically limited by serviceability criteria and computed by integrating the moment-curvature relationship or using tabulated formulas.

A dimensionless ratio of inertial to viscous forces in a flow, used to distinguish laminar from turbulent regimes and to correlate friction and heat transfer data.

A relation expressing head loss in a pipe as a function of friction factor, length-to-diameter ratio, and velocity head, widely used for pressure-drop calculations.

A dimensionless factor applied to velocity head to quantify pressure loss through fittings, valves, and abrupt changes in flow area.

A dimensionless measure of convective heat transfer at a surface relative to conduction through the same fluid layer, used with correlations to find convection coefficients.

The appropriate average temperature driving force for heat exchange between two fluids in parallel or counterflow, calculated from the terminal temperature differences.

A heat exchanger analysis approach that uses effectiveness and number of transfer units to predict performance when outlet temperatures are unknown.

The principle of energy conservation for a system, stating that the net heat added equals the net work done plus the change in internal energy.

The principle that entropy of an isolated system cannot decrease, setting the direction of spontaneous processes and bounding the efficiency of heat engines and refrigerators.

An idealized reversible adiabatic process in which entropy remains constant, used as a benchmark for compressor, turbine, and nozzle efficiency calculations.

A measure of the dispersion of a data set around its mean, equal to the square root of the variance and central to tolerance, uncertainty, and reliability analysis.

A symmetric bell-shaped probability distribution defined by its mean and standard deviation, frequently used to model measurement error and material property scatter.

A range of values, computed from sample data, expected to contain an unknown population parameter with a stated probability over repeated sampling.

A study of how variation in input parameters affects a model's output, used to identify which uncertainties most influence a design decision.

A computational method that repeatedly samples random inputs from specified probability distributions to estimate the distribution of a model's output.

An analysis of how individual part tolerances combine to determine the overall variation of an assembly dimension, using worst-case or statistical methods.

A structured investigation that traces a failure or nonconformity back to its underlying cause rather than its symptoms, often supported by techniques such as fault trees or five-whys questioning.

A systematic tabulation of potential failure modes, their effects and severity, occurrence, and detectability, used to prioritize design or process improvements.

A documented, multidisciplinary examination of a design against requirements at defined stages, intended to catch errors before they become costly or unsafe.

A formal statement of the professional obligations expected of engineers, typically covering public safety, competence, honesty, confidentiality, and avoidance of conflicts of interest.

A situation in which personal, financial, or other interests could improperly influence professional judgment, requiring disclosure and often recusal from the affected decision.

The degree of care and skill that a reasonably prudent practitioner with similar training would exercise under comparable circumstances, used to judge professional conduct.

The professional registration stamp and signature applied to drawings and reports, signifying that the licensed engineer takes responsibility for the work's competence and compliance.

A ranked sequence of hazard mitigation measures, from elimination and substitution through engineering controls and administrative controls to personal protective equipment.

A method of breaking a task into steps and identifying hazards and controls for each step before work begins.

A procedure for isolating and securing hazardous energy sources during maintenance so that equipment cannot be re-energized until locks and tags are removed by authorized personnel.

A formal authorization process for high-risk tasks that documents hazards, required controls, and sign-offs before and during the work.

A standardized document describing a hazardous chemical's properties, health effects, handling precautions, and emergency measures, used to inform safe use and storage.

A consensus document issued by a recognized body that specifies accepted requirements, test methods, or practices for a product, process, or system.

A body of mandatory rules adopted by a jurisdiction, often built on consensus standards, governing the design, construction, or operation of regulated facilities and equipment.

A precise written statement of requirements for materials, products, or workmanship, forming part of a contract and defining what will be accepted.

Planned process activities that build confidence requirements will be met, paired with inspection and testing activities that verify conformance of the delivered work.