<p>Due to the transition in cyclic deformation mechanisms from dislocation slip to deformation twins with increasing total strain amplitude (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\Delta {\varepsilon }_{t}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <msub> <mi>ε</mi> <mi>t</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>/2), a nonlinear relationship between elastic strain amplitude (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\Delta {\varepsilon }_{e}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <msub> <mi>ε</mi> <mi>e</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>/2) and fatigue reversals (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(2{\text{N}}_{f}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <msub> <mtext>N</mtext> <mi>f</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>) was observed in TA5 alloy. This behavior contrasts with previously observed linear relationship between plastic strain amplitude (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\Delta {\varepsilon }_{p}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <msub> <mi>ε</mi> <mi>p</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>/2) and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(2{\text{N}}_{f}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <msub> <mtext>N</mtext> <mi>f</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>. The material exhibited an overall cyclic softening tendency, with the degree of softening progressively diminishing as <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\Delta {\varepsilon }_{t}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <msub> <mi>ε</mi> <mi>t</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>/2 increased, primarily due to the barrier effect of twin boundaries to dislocation motion. Additionally, the tension-compression asymmetry gradually decreased as <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\Delta {\varepsilon }_{t}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <msub> <mi>ε</mi> <mi>t</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>/2 increased, attributed to differences in working hardening behavior and the weakening of Bauschinger effect caused by the deformation twins activation. The activation of deformation twins during cyclic deformation was found to enhance the low cycle fatigue life at high <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\Delta {\varepsilon }_{t}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <msub> <mi>ε</mi> <mi>t</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>/2. This improvement is attributed to a reduction in elastic modulus resulting from crystallographic reorientation induced by deformation twins.</p>