DEFORMATION LOCALIZATION AND SHEAR BAND FRACTURE IN STRONG ANISOTROPY SHEET TENSION

The tensile deformation localization and the shear band fracture behaviors of sheet metals with strong anisotropy are numerically simulated by using Updating Lagrange finite element method, Quasi-how plastic constitutive theory([1]) and B-L planar anisotropy yield criterion([2]). Simulated results are compared with experimental ones. Very good consistence is obtained between numerical and experimental results. The relationship between the anisotropy coefficient R and the shear band angle theta is found.

Clinical study of polydloxanone suture tension band fixation for treatment of patellar fractures

To explore biomechanic characteristics and clinical outcome of absorbable polydloxanone (PDS) treating patellar fractures.Methods The tensile strength test of PDS 0-0 or PDS 1-0 sutures were made in WDW305 electro-universal tester.A total of 60 cases were classified randomly and equally into two groups:treatment group (treated with the absorbable PDS tension hand) and Kirschner wire metals tension band control group (control group).Anatomy reduction was performed with towel clip fixation during operation.Treatment group was managed with diameter 1.5 mm Kirschner wires drilling two pores on the near or distal segment of patellar fracture end are penetrating through two strands of absorbable PDS 0-0 or PDS 1-0 sutures for a satisfactory fracture fixation.Control group was treated with Kirschner wires (2.0 mm in diameter) and steel wire (1.0 mm in diameter) of type “8” tension band fixation.Results Tensile strength testing showed that the biggest tensile of a strand PDS 0-0 sutures was 71.50 N and that of PDS 1-0 97.48 N,when the length was three times more than the initial.Two groups were followed up and the mean fracture healing time was two months,without broken wire or dislocation.Treatment group showed excellent clinical results in 21 cases,good in six and fair in three;while control group showed excellent clinical results in 19 cases,good in seven and fair in four,with no statistical difference compared with treatment group (χ2=0.32,P>0.05).Conclusion Absorbable PDS tension band has better characteristics of mechanics and creepage in treating patellar fractures.It can avoid defects of secondary operation and complications like needle-tail pain and sharped skin resulted from metal tension band fixation.Meanwhile,it is economic and worthy of further clinical application.16 refs,4 figs.

Biomechanical analysis of tension band wiring （TBW） of transverse fractures of patella

Purpose： Tension band wiring is commonly used for fixation of simple transverse fractures. The popular configuration is parallel Kirschner wires （K-wires） and a stainless steel wire loop placed in a vertically oriented figure-of-8. Methods： We used a wooden model of a patella with a midway transverse fracture and compared four different types of fixation. The first construct had a vertical figure-of-8 with one twist of wire. The second contained a vertical figure-of-8 with two twists of wire. The third was a vertical figure-of-8 with two twists of wire placed at adjacent corners while the last one had a horizontal figure-of-8 with two twists of wire placed at adjacent corners, lnterfragmentary compression at the point of wire breakage was measured for each construct as well as permanent displacement on cyclic loading. Results： Placement of the figure-of-eight in a horizontal orientation with two wire twists at the corner improved interfragmentary compression by 63% （p 〈 0.05, Tukey post ]hoc test）. On cyclic loading, all the constructs with vertical figure-of-eight but none with a horizontal construct failed （p = 0.01; Fisher＇s exact test）. Permanent fracture displacement after cyclic loading was ,57% lower with horizontal figure- of-eight constructs （p 〈 0.05; t test）. Conclusion： Placing wire twists at the corner and a horizontal placement of figure-of-8 improves stability of the construct.

Critical Shear Offset of Fracture in a Zr-based Metallic Glass

The nanoscale shear band operation process of Zr_（55）Pd_（10）Cu_（20）Ni_5Al_（10） metallic glass（MG）was reined in by constant force during well-designed loading-holding-unloading cyclic microcompression test.Through the test,it is revealed that the whole shear banding process involves three stages：shear band initiation,shear sliding and shear band arrest.Based on the energy balance principle,the size-affected speed of shear sliding is interpreted.The energy originated from the shear sliding leads to heat-up of the shear plane;therefore,the temperature in shear band increases with the size of shear offset caused by the energy accumulation during shear sliding.Taking the glass transition temperature as the critical temperature of fracture for the Zr-based MG,the critical shear offset is predicted to be approximately 190μm,fully in line with the experimental observation.This directly proved that the fracture of the MG is caused by the temperature rise during shear sliding.