Determine steady-state creep rate from experimental extension data.
Millimeters (mm) or Inches (in)
Hours (h)
Measurement at Start Time (mm/in)
Measurement at End Time (mm/in)
Calculation Results
Change in Extension:–
Change in Strain (Δε):–
Creep Rate (%/hr):–
Creep Rate (hr⁻¹):–
What is Creep Rate?
Creep is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods and typically increases as they near their melting point.
The Creep Rate ($\dot{\epsilon}$) is the slope of the creep strain vs. time curve. In engineering applications, particularly for components like turbine blades, boilers, and high-pressure piping, knowing the steady-state creep rate is vital for predicting the lifespan of the material.
How to Calculate Creep Rate
This calculator determines the creep rate based on experimental data collected from a creep test. The calculation follows the basic definition of strain rate during the secondary (steady-state) creep stage.
$\epsilon$ (Strain): Calculated as $\frac{\Delta L}{L_0}$ (Change in length divided by original gauge length).
$t$ (Time): The duration over which the change occurs.
By measuring the extension of a specimen at two different points in time during the steady-state phase, we can derive the rate at which the material is deforming.
Stages of Creep
Creep deformation generally occurs in three distinct stages:
Primary (Transient) Creep: The creep rate starts high and decreases rapidly with time. This is due to work hardening of the material.
Secondary (Steady-State) Creep: The creep rate becomes relatively constant. This is the most important stage for engineering design and is the value calculated by this tool. The balance between work hardening and recovery (softening) processes maintains a constant rate.
Tertiary Creep: The creep rate accelerates exponentially until the material fractures (rupture). This is often associated with the formation of internal voids or necking.
Factors Influencing Creep
The rate of creep is highly dependent on material properties, exposure time, exposure temperature, and the applied structural load.
Temperature: Creep generally becomes significant at temperatures above 0.4 times the melting temperature of the material ($T_m$).
Stress: Higher applied stress levels result in faster creep rates and shorter times to rupture.
Material Structure: Grain size plays a role; single-crystal materials (like those used in modern turbine blades) have higher creep resistance than polycrystalline materials because grain boundaries allow for sliding.
function calculateCreepRate() {
// Get input elements
var gaugeLengthInput = document.getElementById("gaugeLength");
var timeDurationInput = document.getElementById("timeDuration");
var initialExtensionInput = document.getElementById("initialExtension");
var finalExtensionInput = document.getElementById("finalExtension");
var errorDiv = document.getElementById("crcError");
var resultDiv = document.getElementById("crcResult");
// Parse values
var L0 = parseFloat(gaugeLengthInput.value);
var dt = parseFloat(timeDurationInput.value);
var dL1 = parseFloat(initialExtensionInput.value);
var dL2 = parseFloat(finalExtensionInput.value);
// Validation
errorDiv.style.display = "none";
resultDiv.style.display = "none";
if (isNaN(L0) || isNaN(dt) || isNaN(dL1) || isNaN(dL2)) {
errorDiv.innerHTML = "Please enter valid numeric values for all fields.";
errorDiv.style.display = "block";
return;
}
if (L0 <= 0) {
errorDiv.innerHTML = "Original Gauge Length must be greater than zero.";
errorDiv.style.display = "block";
return;
}
if (dt <= 0) {
errorDiv.innerHTML = "Time Interval must be greater than zero.";
errorDiv.style.display = "block";
return;
}
if (dL2 < dL1) {
errorDiv.innerHTML = "Final extension cannot be less than initial extension (unless material is shrinking, which is atypical for creep).";
errorDiv.style.display = "block";
return;
}
// Calculations
// 1. Calculate Change in Extension
var deltaExtension = dL2 – dL1;
// 2. Calculate Strains (Engineering Strain = Extension / Original Length)
// Note: Extension inputs are usually Total Extension from L0, or delta L.
// Assuming inputs are "Extension" (delta L), then Strain = Extension / L0.
var strain1 = dL1 / L0;
var strain2 = dL2 / L0;
// 3. Calculate Change in Strain
var deltaStrain = strain2 – strain1;
// 4. Calculate Creep Rate
// Rate = Change in Strain / Time
var creepRateStandard = deltaStrain / dt; // Units: hr^-1
var creepRatePercent = creepRateStandard * 100; // Units: %/hr
// Display Results
document.getElementById("resDeltaExtension").innerHTML = deltaExtension.toFixed(4) + " units";
document.getElementById("resDeltaStrain").innerHTML = deltaStrain.toExponential(4) + " (mm/mm)";
document.getElementById("resRatePercent").innerHTML = creepRatePercent.toExponential(4) + " %/hr";
document.getElementById("resRateStandard").innerHTML = creepRateStandard.toExponential(4) + " hr⁻¹";
resultDiv.style.display = "block";
}