Nasir Hayat

On the Effect of Curvature Radius on the Spif-Ability

Single Point Incremental Forming (SPIF) is a novel sheet metal forming process. The formability (i.e. spif-ability) in this process is determined through Varying Wall Angle Conical Frustum (VWACF) test. In this paper, the effect of variation in the curvature radius, a geometrical parameter of test, on the test results is investigated. A series of VWACF tests with a variety of curvature radii is performed to quantify the said effect. It is found that the spif-ability increases with increasing of curvature radius. However, any variation in the curvature radius does not affect the spif-ability when the normalized curvature radius (i.e. curvature radius/tool radius) becomes higher than 9.

New Methodologies for the Determination of Precise Forming Limit Curve in Single Point Incremental Forming Process

Straight groove test is a widely-used formability test in Single Point Incremental Forming (SPIF). This test does not cover all the forming aspects of SPIF process, however. In order to ascertain its legitimacy, two new tests covering necessary SPIF aspects are devised. The FLC of an aluminum sheet is determined using the newly proposed and straight groove tests. It is found that the straight groove test shows much lower formability than the new tests. Therefore, the employment of newly devised test(s) is proposed for the determination of precise formability limits.

Role of Material Properties in Improving Sheet Formability in SPIF Process

Single point incremental forming (SPIF) is a novel sheet metal forming process. Owing to unique deformation mechanism, this process improves the sheet formability as compared to the conventional stamping process. In the current paper, the mechanical properties and spifability (i.e. formability in SPIF) of a wide range of materials were tested. The mechanical properties were mainly determined through tensile testing and the spifability was evaluated using Varying Wall Angle Conical Frustum (VWACF) test. Each mechanical property was drawn against the improvement in sheet formability (i.e. difference of spifability and stampability) and the sole most influential property was identified. It was found that the improvement in formability increases with the increasing of true thickness strain at tensile fracture.

Response of closed Glass Fiber Reinforced Polymer sections under combined bending and torsion

Structural response under combined bending (M) and torsion (T) of pultruded Glass Fiber Reinforced Polymer composite hollow circular and square sections has been investigated, using unique experimental facility for combined loads. Prior to determining combined response, bending and torsional strengths at failure were found separately for all test sections. To evaluate structural response, strain gages were attached at 6 to 12 critical locations of each specimen. For each cross-section, three samples were tested under combined load combinations, i.e. (0.25 Mmax, TFailure), (0.50 Mmax, TFailure) and (0.75 Mmax, TFailure). The results have been presented as M vs ɛ, T vs θ, and M / M max vsT / T max . Local bending effect are found to be significant under point loads, even though they are distributed over a small area. The interactive plots exhibited three distinct zones, i.e. bending moment dominated zone, torque dominated zone, and transition zone. The failure modes revealed a distinct pattern with crack initiation sites and propagation directions. The potential energy method of bent and twisted specimens of isotropic thin-walled sections has been extended to thin-walled orthotropic members. Finite element analyses using ANSYS-SHELL181 was carried out to develop torsion-bending interaction response and compare with experimental data. Principal strain to failure predictions under combined loads, except under pure bending, resulted in a constant strain to failure for a given fiber architecture.