Development of micro-form-fitted amorphous thermoplast/light metal hybrid components

In order to meet the high demands on tolerances and surface qualities, for example in automotive lighting applications, a hybrid part composed of a light metal (aluminium) and an amorphous thermoplastic (polycarbonate) could be an alternative to the established mono-materials used today. Due to the lack of adhesion promoter systems for joining this specific material combination, a micro-form-fitted connection by creating undercut microstructures by laser ablation is used to achieve a full-surface bond. First investigations are carried out to ensure the filling of these microstructures with different polycarbonate moulding compounds by over moulding in the injection moulding process. Subsequently, the influence of the moulding compound, the structure arrangement and the influence of a pickling treatment on the bond strength are analysed by tensile shear testing.     

The influence of coefficient of friction in thermal prediction of refill friction stir spot welding process of AA7075-T6

Numerical modelling of refill friction stir spot welding helps in the deep investigation of physics involved in the joining process. The current study investigates four variants of contact models and their influence on thermal prediction in the process. The contact models with constant shear and coulomb friction coefficients and temperature-dependent shear and coulomb friction coefficients were used in the numerical models to investigate the influence of friction coefficients in the prediction of thermal cycles in refill friction stir spot welding. The results from the numerical model are compared and validated with the experimental results from a previous study. The contact model with temperature-dependent coulomb friction coefficient was concluded to be more reliable when compared to the other three contact models. The temperature for this contact model at the centre of the weld is 505 °C, which differs from the temperature recorded in the experiment by 2 %. The peak temperatures of numerical models with constant coulomb and shear friction coefficients differ from the experimental temperature at the weld centre by 5.17 % and 16.8 % respectively.     

Über die Anpassung eines fortschrittlichen Stützwirkungsansatzes für das Kerbspannungskonzept

On the calibration of an advanced support approach for the effective notch stress concept – applying an implicit gradient approach as replacement for the notch rounding in the fatigue life assessment of welded joints. The proof of fatigue life for welded structures according to the notch stress concept requires the calculation of stresses on a geometry with rounded notches in the weld toe and the weld root. The roundings prevent singularities in stress calculation as well as simulate notch sensitivity. In this paper an advanced method for modelling the micro support theory without rounded notches, is presented.     

Evolution of microstructure and mechanical characteristics of friction stir welded ultrafine-grained aluminum alloy 6082

Bulk production of ultrafine-grained material is in great demand presently. Ultrafine-grained material can be synthesized using accumulative roll bonding, which is a prominent severe plastic deformation technique to develop such materials in bulk. There are further challenges in the fabrication of ultrafine-grained material. Friction stir welding is a potential technique to join the ultrafine-grained material while maintaining its mechanical and microstructural characteristics stability as no fusion is required. The present research work demonstrates the microstructural and mechanical characteristics of various welding zone after friction stir welding of ultrafine-grained aluminum alloy 6082. The microstructural features were examined using optical microscopy and the electron back-scattered diffraction technique. The variation in mechanical characteristics was observed using tensile and microhardness tests. The fractography of tensile specimens was studied to identify the mode of failure. The present study demonstrates the viability of friction stir welding to join ultrafine-grained aluminum alloy 6082 developed by accumulative roll bonding. The ultrafine grain size of 0.52 μm was achieved after four accumulative roll bonding cycles. The microhardness of accumulative roll bonding processed samples and the tensile strength of the weld joint were increased about two times and 1.6 times respectively compared to the annealed sample.     

施肥与灌溉对黑土区稻田氮素渗漏淋溶的影响

为明确东北黑土区稻田土壤氮素渗漏规律,在典型黑土区开展了基于农田水平衡的小区试验,分析了不同灌溉方式和施氮水平条件下稻田土壤渗漏水中三氮浓度变化情况,并结合农田水平衡方程计算出了不同水肥条件下的氮素淋失总量。结果表明,渗漏水中铵态氮、硝态氮和总氮浓度与施氮量呈正相关关系,控制灌溉和浅湿灌溉分别可以减少硝态氮渗漏浓度11.89%和14.15%;常规灌溉方式下每公顷每增加1kg施氮量(折合成纯氮),氮素淋失量增加0.117 5kg,控制灌溉和浅湿灌溉则分别增加0.035 9kg和0.055 7kg;在水稻全生育期,控制灌溉氮素淋失总量最小,平均为4.51kg/hm2,约是常规灌溉的1/3、浅湿灌溉的1/2。综合分析认为,浅湿灌溉是适用性更高的灌溉方式,理论合理施肥量为137.30kg/hm2。