RESUMEN

While the third generation of advanced high-strength steels (3rd Gen AHSS) have increasingly gained attention for automotive lightweighting, it remains unclear to what extent the developed methodologies for the conventional dual-phase (DP) steels are applicable to this new class of steels. The present paper provides a comprehensive study on the constitutive, formability, tribology, and fracture behavior of three commercial 3rd Gen AHSS with an ultimate strength level ranging from 980 to 1180 MPa which are contrasted with two DP steels of the same strength levels and the 590R AHSS. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then evaluated in 3D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen 1180 AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels was similar but with a stark contrast in the local formability whereas the opposite trend was observed for the 3rd Gen 980 and the DP980 steel. The forming limit curves could be accurately predicted using the experimentally measured hardening behavior and the deterministic modified Bressan-Williams through-thickness shear model or the linearized Modified Maximum Force Criterion. The resistance to sliding of the three 3rd Gen AHSS in the Twist Compression Test revealed a comparable coefficient of friction to the 590R except for the electro-galvanized 3rd Gen 1180 V1. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion, biaxial punch tests, and the VDA 238-100 bend test were performed to construct stress-state dependent fracture loci for use in forming and crash simulations. It is demonstrated that, the 3rd Gen 1180 V2 can potentially replace the DP980 steel in terms of both the global and local formability.

RESUMEN

OBJECTIVE: To investigate the effect of the position of the apical portion of closing loops on the force system at both loop ends. MATERIALS AND METHODS: T-loops were compared with backward-sloped L-loops (SL) and reversed L-loops (RL). SL-loops were directed toward the anterior side; RL-loops were directed toward the posterior side. Loop response to loop pulling was determined with finite element analysis at six positions of the apical loop portion for 12-mm interbracket distance and 8-mm loop length and height. Three-dimensional models of the closing loops were created using beam elements with the properties of stainless steel. Loop responses (horizontal load/deflection, vertical force, and moment-to-force ratio) at both loop ends were calculated as well as at 100 g and 200 g activation forces. RESULTS: T-, SL-, and RL-loops with the same position of the apical portion showed approximately the same force system at both loop ends. This behavior was found across the investigated range through which the loops were moved (interbracket center to posterior bracket). CONCLUSIONS: The center of the apical portion determined the force system of the closing loops regardless of the position of the loop legs. The centers of the apical portion of the T-, SL-, and RL-loops acted like V-bend positions.

Asunto(s)

Fenómenos Mecánicos , Diseño de Aparato Ortodóncico , Técnicas de Movimiento Dental/instrumentación , Fenómenos Biomecánicos , Aleaciones Dentales , Análisis de Elementos Finitos , Humanos , Ensayo de Materiales , Alambres para Ortodoncia , Acero Inoxidable , Estrés Mecánico

RESUMEN

OBJECTIVE: To investigate the effect of vertical steps on a T-loop force system at three interbracket distances (IBDs) and their association with V-bends. MATERIALS AND METHODS: Loop response during simulated loop pulling was determined for 18 T-loop configurations (6-, 9-, and 12-mm IBD with a 2.5-mm canine bracket (CB) end and 0- (plain), 0.5-, or 1-mm vertical step). Loop length-by-height was 8 × 8 or 10 × 10 mm. Horizontal load/deflection, vertical force (Fy), and moment-to-force (M/F) ratios at loop ends were determined for 100-g and 200-g activation by finite element analysis. RESULTS: Plain, 12-mm IBD T-loops showed similar force and moment responses as off-centered V-bends (greater moment close to V-bend) without change in moment direction at the premolar bracket (PB) end; plain, 6-mm IBD T-loop responses were similar to those of centered V-bends (equal, opposing moments at each end). Adding vertical steps to the T-loops raised the M/F ratio at the PB ends enough to produce root movement, while lowering the M/F ratios at the CB ends. Increasing the step bends for shorter IBDs increased Fys and caused rapid changes in M/F ratios. Unlike plain T-loops, increasing activation in stepped T-loops caused substantial variations in M/F ratios and in amount and direction of Fys. CONCLUSIONS: Step bends can dramatically change the force system. Stepped T-loops display combined effects of V-bends and step bends.

Asunto(s)

Análisis de Elementos Finitos , Diseño de Aparato Ortodóncico , Diente Premolar , Análisis del Estrés Dental , Humanos , Alambres para Ortodoncia , Estrés Mecánico , Técnicas de Movimiento Dental

RESUMEN

Objective To analyze the mechanical properties of V-bends with different materials, sizes of arch wires, angles, shapes, inter-bracket distances by using finite element method, so as to provide references for clinical practice of V-bends. Methods The finite element models of V-bends were established, including two kinds of materials (stainless steel, titanium-molybdenum alloy), two sizes（0.43 mm×0.64 mm, 0.48 mm×0.64 mm）, two V-bend positions, two angles(150°, 165°),and two inter-bracket distances（7,10 mm）, so as to compare and analyze their mechanical properties after simulative loading. Results The maximum force values produced by V-bends with stainless steel arch wire were greater than that of V-bends with β titanium steel arch wire. The force produced by V-bends with 0.43 mm×0.64 mm arch wire was smaller than that produced by V-bends with 0.48 mm×0.64 mm arch wire. The size of arch wire had a more obvious impact on V-bends with symmetrical arch wire. The force of V-bends with asymmetric arch wire was more evidently influenced by the change of inter-bracket distance. For V-bends with the same shape, the smaller the V-shaped angle, the greater the force on the bracket would be. Conclusions The V-bends with different materials, different sizes of arch wires, different shapes and inter-bracket distances will have different mechanical behaviors. In clinical application, the materials, sizes of arch wires, shapes and angles of V-bends should be adjusted properly according to the inter-bracket distances.