**Arc**. Part of the circumference of a curve. The curved portion of a bend.

**Arc length**. The curved distance along a circumferential line. The length of the curved portion of a member.

**Bend radius**. The radius of curvature, measured to a reference point on the cross section.

**Center-to-center**. The distance between tangent points of two adjoining bends.

**Chord**. The straight distance between two points on a curve.

**Cold bending**. Any bending process where curvature is induced by load application at room temperature.

**Compound bend**. A curve made up of two or more arcs in the same plane, joined tangentially without reversal of curvature.

**Degree of bend**. The angle to which a bend is formed.

**Distortion**. A deviation from the original cross-sectional shape.

**Ductility.** The ability of the material to deform without fracture.

**Easy way.** The orientation of a member where bending occurs about the weak principal axis.

**Gag pressing**. A cold-bending method that uses hydraulic rams to simultaneously apply bending forces at discrete, widely-spaced, locations along the member. Also known as point bending.

**Grip**. An additional straight length at each end of a curved member required in the bending operation. Also known as “hold and tail” or “lead and tail” to emphasize the additional length is required at each end of the member.

**Hard way**. The orientation of a member where bending occurs about the strong principal axis.

**Heat curving**. A bending process that relies only on the application of heat in specific patterns to induce curvature.

**Horizontally curved member**. A member with curvature in the horizontal plane.

**Hot bending.** Any bending process where curvature is induced by load application at an elevated temperature.

**In-plane flexure**. Bending of a curved member where moment is applied about the axis of curvature. The primary flexural stresses and deflections are in the plane of curvature.

**Incremental step bending**. A cold-bending method that uses hydraulic rams to apply bending forces at several discrete, closely spaced locations along the member.

**Induction bending**. A hot-bending method that utilizes an electric induction coil to heat a short section of the member before it is curved by force.

**Local buckling**. A type of potential cross-sectional distortion that is caused by compression stresses in the member induced during the bending operation. Local buckling can be in the form of a single half-wave or a series of wrinkles along the entire bend length. Also known as waving or wrinkling.

**Mandrel**. A tool that can be inserted into a HSS member to support the walls and minimize cross-sectional distortion during the bending process.

**Multi-axis bend.** A bend with curvature about more than one axis. Also known as a multi-plane bend.

**Normalizing**. A thermal treatment where the member is heated to a suitable temperature above the upper transformation temperature, followed by cooling in still air at room temperature.

**Off-axis bend**. A bending orientation where the member is curved about a non-principal or non-geometric axis. Also known as conical rolling.

**Oil-canning**. A form of local buckling that can cause collapse of the cross section due to the combined effect of ovalization and local buckling in a single half-wave.

**Out-of-plane flexure**. Bending of a curved member where moment is applied in the plane of curvature. The primary flexural stresses and deflections are in perpendicular to the plane of curvature.

**Ovality**. The cross-sectional distortion of a round HSS where the deviation from the theoretical shape forms an oval.

**Pyramid roll bending**. A cold-bending operation where a member is bent progressively by repeatedly passing it through a set of three adjustable rolls in a pyramid arrangement.

**Reverse-compound bend**. A curve made up of two or more arcs in the same plane, joined tangentially with reversal of curvature. Also known as an S-curve or an offset bend.

**Rise**. The distance, perpendicular to the chord, between the mid-point of a chord and an arc. Also known as the mid-ordinate.

**Rotary-draw bending.** A bending method where the member is clamped to a form and bent by rotating it around a bend die.

**Slope**. The angle of an inclined member designated using the vertical (rise) and horizontal (run) distances between two points. Also known as bevel or pitch.

**Snap-through buckling**. A type of instability where the load-displacement diagram descends after reaching a limit point and the structure abruptly transforms from one equilibrium state to another remote equilibrium state on the ascending, stable portion of the curve.

**Spiral.** A three-dimensional curve with an arc in one plane and a constant slope in a perpendicular plane. Also known as a helix or helical curve. The curving process is often called sloped rolling or pitched rolling.

**Springback**. The deformation of a bent member immediately after a bending load is released, where a portion of the curvature is lost.

**Strake.** A protruding fin that can be connected to a structure to improve aerodynamic stability.

**Synchronized incremental cold bending**. A cold-bending process where synchronized forces are applied at several locations along the member.

**Tangent**. A straight line, perpendicular to the radius, that touches a curve at a single point. A straight member adjacent to a curved segment.

**Tangent point**. The start or end point of a curve.

**Variable-radius bend.** Parabolic, elliptical and other noncircular bends with variable radii. Also known as multiradius and a non-circular bends.

**Vertically curved member**. A member with curvature in the vertical plane.

**Waving**. See Local buckling.

**Wrinkling**. See Local buckling.

**Yield point.** The curvature at which a member will deform permanently during bending.

**Further reading: **Bending Metal