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True strain

Materials Science · FE Reference Handbook section

Materials Science
6 formulas
10 exam-style examples
~57 min
All Materials Science lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • Atomic Melting Melting Specific Heat (W/(m˙K))

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
True strain — solve for true strain — True strain

A materials engineer computes the true strain of a tensile specimen at necking. Given original length (L0) = 1.3500 in; final length (Lf) = 2.9000 in, determine the true strain (epsT).

Given

  • originallength(L0)=1.3500inoriginal length (L_{0}) = 1.3500 in
  • finallength(Lf)=2.9000infinal length (Lf) = 2.9000 in

Find

true strain (epsT)

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except epsT is given, so isolate epsT symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 1 — schematic for True strain — solve for true strain — True strain

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for epsT:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  3. Step 3

    Listthegivens:originallength(L0)=1.3500in,finallength(Lf)=2.9000inList the givens: original length (L_{0}) = 1.3500 in, final length (Lf) = 2.9000 in
  4. Step 4 — Substitute the given values:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  5. Step 5 — Evaluate:

    epsT=0.7646epsT = 0.7646
  6. Step 6 — Check: returning epsT = 0.7646 to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
epsT=0.7646epsT = 0.7646

Why the other options are there

  • 1.5292 — kept a factor of two that cancels in the correct rearrangement.
  • 0.3823 — dropped that same factor in the other direction.
  • 0.8411 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 2
True strain — solve for final length — True strain (2)

A student compares true strain to engineering strain for a stretched rod. Given original length (L0) = 2.2000 in; true strain (epsT) = 1.1610, determine the final length (Lf) in in.

Given

  • originallength(L0)=2.2000inoriginal length (L_{0}) = 2.2000 in
  • truestrain(epsT)=1.1610true strain (epsT) = 1.1610

Find

final length (Lf), in in

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except Lf is given, so isolate Lf symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 2 — schematic for True strain — solve for final length — True strain (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for Lf:

    Lf=L0eεTLf = L_0 e^{\varepsilon_T}
  3. Step 3

    Listthegivens:originallength(L0)=2.2000in,truestrain(epsT)=1.1610List the givens: original length (L_{0}) = 2.2000 in, true strain (epsT) = 1.1610
  4. Step 4 — Substitute the given values:

    Lf=L0eεTLf = L_0 e^{\varepsilon_T}
  5. Step 5 — Evaluate:

    Lf=7.0249 inLf = 7.0249\ \text{in}
  6. Step 6 — Check: returning Lf = 7.0249 in to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
Lf=7.0249 inLf = 7.0249\ \text{in}

Why the other options are there

  • 14.0497 — kept a factor of two that cancels in the correct rearrangement.
  • 3.5124 — dropped that same factor in the other direction.
  • 7.7274 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 3
True strain — solve for original length — True strain (3)

The true strain of a drawn wire is calculated from its length change. Given final length (Lf) = 6.0500 in; true strain (epsT) = 0.7750, determine the original length (L0) in in.

Given

  • finallength(Lf)=6.0500infinal length (Lf) = 6.0500 in
  • truestrain(epsT)=0.7750true strain (epsT) = 0.7750

Find

original length (L0), in in

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except L0 is given, so isolate L0 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 3 — schematic for True strain — solve for original length — True strain (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for L0:

    L0=Lfe−εTL_{0} = L_f e^{-\varepsilon_T}
  3. Step 3

    Listthegivens:finallength(Lf)=6.0500in,truestrain(epsT)=0.7750List the givens: final length (Lf) = 6.0500 in, true strain (epsT) = 0.7750
  4. Step 4 — Substitute the given values:

    L0=Lfe−εTL_{0} = L_f e^{-\varepsilon_T}
  5. Step 5 — Evaluate:

    L0=2.7873 inL_{0} = 2.7873\ \text{in}
  6. Step 6 — Check: returning L0 = 2.7873 in to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
L0=2.7873 inL_{0} = 2.7873\ \text{in}

Why the other options are there

  • 5.5745 — kept a factor of two that cancels in the correct rearrangement.
  • 1.3936 — dropped that same factor in the other direction.
  • 3.0660 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 4
True strain — solve for true strain (case 2) — True strain (4)

A materials engineer computes the true strain of a tensile specimen at necking. Given original length (L0) = 4.2500 in; final length (Lf) = 6.4000 in, determine the true strain (epsT).

Given

  • originallength(L0)=4.2500inoriginal length (L_{0}) = 4.2500 in
  • finallength(Lf)=6.4000infinal length (Lf) = 6.4000 in

Find

true strain (epsT)

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except epsT is given, so isolate epsT symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 4 — schematic for True strain — solve for true strain (case 2) — True strain (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for epsT:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  3. Step 3

    Listthegivens:originallength(L0)=4.2500in,finallength(Lf)=6.4000inList the givens: original length (L_{0}) = 4.2500 in, final length (Lf) = 6.4000 in
  4. Step 4 — Substitute the given values:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  5. Step 5 — Evaluate:

    epsT=0.4094epsT = 0.4094
  6. Step 6 — Check: returning epsT = 0.4094 to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
epsT=0.4094epsT = 0.4094

Why the other options are there

  • 0.8188 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2047 — dropped that same factor in the other direction.
  • 0.4503 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 5
True strain — solve for final length (case 2) — True strain (5)

A student compares true strain to engineering strain for a stretched rod. Given original length (L0) = 1.8000 in; true strain (epsT) = 0.1170, determine the final length (Lf) in in.

Given

  • originallength(L0)=1.8000inoriginal length (L_{0}) = 1.8000 in
  • truestrain(epsT)=0.1170true strain (epsT) = 0.1170

Find

final length (Lf), in in

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except Lf is given, so isolate Lf symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 5 — schematic for True strain — solve for final length (case 2) — True strain (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for Lf:

    Lf=L0eεTLf = L_0 e^{\varepsilon_T}
  3. Step 3

    Listthegivens:originallength(L0)=1.8000in,truestrain(epsT)=0.1170List the givens: original length (L_{0}) = 1.8000 in, true strain (epsT) = 0.1170
  4. Step 4 — Substitute the given values:

    Lf=L0eεTLf = L_0 e^{\varepsilon_T}
  5. Step 5 — Evaluate:

    Lf=2.0234 inLf = 2.0234\ \text{in}
  6. Step 6 — Check: returning Lf = 2.0234 in to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
Lf=2.0234 inLf = 2.0234\ \text{in}

Why the other options are there

  • 4.0468 — kept a factor of two that cancels in the correct rearrangement.
  • 1.0117 — dropped that same factor in the other direction.
  • 2.2258 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 6
True strain — solve for original length (case 2) — True strain (6)

The true strain of a drawn wire is calculated from its length change. Given final length (Lf) = 2.1000 in; true strain (epsT) = 1.0640, determine the original length (L0) in in.

Given

  • finallength(Lf)=2.1000infinal length (Lf) = 2.1000 in
  • truestrain(epsT)=1.0640true strain (epsT) = 1.0640

Find

original length (L0), in in

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except L0 is given, so isolate L0 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 6 — schematic for True strain — solve for original length (case 2) — True strain (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for L0:

    L0=Lfe−εTL_{0} = L_f e^{-\varepsilon_T}
  3. Step 3

    Listthegivens:finallength(Lf)=2.1000in,truestrain(epsT)=1.0640List the givens: final length (Lf) = 2.1000 in, true strain (epsT) = 1.0640
  4. Step 4 — Substitute the given values:

    L0=Lfe−εTL_{0} = L_f e^{-\varepsilon_T}
  5. Step 5 — Evaluate:

    L0=0.7247 inL_{0} = 0.7247\ \text{in}
  6. Step 6 — Check: returning L0 = 0.7247 in to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
L0=0.7247 inL_{0} = 0.7247\ \text{in}

Why the other options are there

  • 1.4493 — kept a factor of two that cancels in the correct rearrangement.
  • 0.3623 — dropped that same factor in the other direction.
  • 0.7971 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 7
True strain — solve for true strain (case 3) — True strain (7)

A materials engineer computes the true strain of a tensile specimen at necking. Given original length (L0) = 2.4000 in; final length (Lf) = 1.5000 in, determine the true strain (epsT).

Given

  • originallength(L0)=2.4000inoriginal length (L_{0}) = 2.4000 in
  • finallength(Lf)=1.5000infinal length (Lf) = 1.5000 in

Find

true strain (epsT)

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except epsT is given, so isolate epsT symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 7 — schematic for True strain — solve for true strain (case 3) — True strain (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for epsT:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  3. Step 3

    Listthegivens:originallength(L0)=2.4000in,finallength(Lf)=1.5000inList the givens: original length (L_{0}) = 2.4000 in, final length (Lf) = 1.5000 in
  4. Step 4 — Substitute the given values:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  5. Step 5 — Evaluate:

    epsT=−0.4700epsT = -0.4700
  6. Step 6 — Check: returning epsT = -0.4700 to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
epsT=−0.4700epsT = -0.4700

Why the other options are there

  • -0.9400 — kept a factor of two that cancels in the correct rearrangement.
  • -0.2350 — dropped that same factor in the other direction.
  • -0.5170 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 8
True strain — solve for final length (case 3) — True strain (8)

A student compares true strain to engineering strain for a stretched rod. Given original length (L0) = 4.6500 in; true strain (epsT) = 0.7850, determine the final length (Lf) in in.

Given

  • originallength(L0)=4.6500inoriginal length (L_{0}) = 4.6500 in
  • truestrain(epsT)=0.7850true strain (epsT) = 0.7850

Find

final length (Lf), in in

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except Lf is given, so isolate Lf symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 8 — schematic for True strain — solve for final length (case 3) — True strain (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for Lf:

    Lf=L0eεTLf = L_0 e^{\varepsilon_T}
  3. Step 3

    Listthegivens:originallength(L0)=4.6500in,truestrain(epsT)=0.7850List the givens: original length (L_{0}) = 4.6500 in, true strain (epsT) = 0.7850
  4. Step 4 — Substitute the given values:

    Lf=L0eεTLf = L_0 e^{\varepsilon_T}
  5. Step 5 — Evaluate:

    Lf=10.1947 inLf = 10.1947\ \text{in}
  6. Step 6 — Check: returning Lf = 10.1947 in to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
Lf=10.1947 inLf = 10.1947\ \text{in}

Why the other options are there

  • 20.3894 — kept a factor of two that cancels in the correct rearrangement.
  • 5.0973 — dropped that same factor in the other direction.
  • 11.2142 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 9
True strain — solve for original length (case 3) — True strain (9)

The true strain of a drawn wire is calculated from its length change. Given final length (Lf) = 1.5000 in; true strain (epsT) = 0.9680, determine the original length (L0) in in.

Given

  • finallength(Lf)=1.5000infinal length (Lf) = 1.5000 in
  • truestrain(epsT)=0.9680true strain (epsT) = 0.9680

Find

original length (L0), in in

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except L0 is given, so isolate L0 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 9 — schematic for True strain — solve for original length (case 3) — True strain (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for L0:

    L0=Lfe−εTL_{0} = L_f e^{-\varepsilon_T}
  3. Step 3

    Listthegivens:finallength(Lf)=1.5000in,truestrain(epsT)=0.9680List the givens: final length (Lf) = 1.5000 in, true strain (epsT) = 0.9680
  4. Step 4 — Substitute the given values:

    L0=Lfe−εTL_{0} = L_f e^{-\varepsilon_T}
  5. Step 5 — Evaluate:

    L0=0.5698 inL_{0} = 0.5698\ \text{in}
  6. Step 6 — Check: returning L0 = 0.5698 in to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
L0=0.5698 inL_{0} = 0.5698\ \text{in}

Why the other options are there

  • 1.1395 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2849 — dropped that same factor in the other direction.
  • 0.6267 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

Example 10
True strain — solve for true strain (case 4) — True strain (10)

A materials engineer computes the true strain of a tensile specimen at necking. Given original length (L0) = 1.6000 in; final length (Lf) = 2.6500 in, determine the true strain (epsT).

Given

  • originallength(L0)=1.6000inoriginal length (L_{0}) = 1.6000 in
  • finallength(Lf)=2.6500infinal length (Lf) = 2.6500 in

Find

true strain (epsT)

Start with the thinking

  • The governing relation printed in this handbook section is True strain.
  • Everything except epsT is given, so isolate epsT symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • True strain uses the natural log of the length ratio, unlike engineering strain's linear ratio.
True strain test specimenPL0 -> Lf

Figure 10 — schematic for True strain — solve for true strain (case 4) — True strain (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)
  2. Step 2 — Rearrange symbolically for epsT:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  3. Step 3

    Listthegivens:originallength(L0)=1.6000in,finallength(Lf)=2.6500inList the givens: original length (L_{0}) = 1.6000 in, final length (Lf) = 2.6500 in
  4. Step 4 — Substitute the given values:

    epsT=ln⁡(Lf/L0)epsT = \ln(L_f/L_0)
  5. Step 5 — Evaluate:

    epsT=0.5046epsT = 0.5046
  6. Step 6 — Check: returning epsT = 0.5046 to

    εT=ln⁡ ⁣(LfL0)\varepsilon_T = \ln\!\left(\dfrac{L_f}{L_0}\right)

    reproduces the given quantities, and both sides carry the same units.

Answer:
epsT=0.5046epsT = 0.5046

Why the other options are there

  • 1.0091 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2523 — dropped that same factor in the other direction.
  • 0.5550 — rounded an intermediate value before the final step.

Reference: FE Handbook — True Strain

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