非垂直激光切割能量分布研究

为实现激光非垂直切割高分子材料,建立了激光非垂直切割模型。通过求解阈值能量方程,得到切缝宽度和热影响区(HAZ)宽度随激光线能量、入射角和离焦量的变化规律。在CO_2连续激光切割系统上,采用正交试验法,针对聚对苯二甲酸乙二醇酯(PET)薄膜材料进行切割试验,发现入射角在-57.3°57.3°范围内、离焦量在-1515mm范围内时,切缝宽度和HAZ宽度变化平缓,切割质量良好。结果表明,模型能够很好地预测激光非垂直切割高分子材料时的切缝宽度和HAZ宽度,为激光切割复杂曲面膜片提供了参数指导。

一种新的哼唱音符音高划分方法

哼唱音符音高的准确划分，对哼唱音乐检索系统识别率的提高起着很大的作用。目前，大部分的哼唱音乐检索系统都是采用能量划分的方法，在很大程度上并不能对哼唱波形文件顺利完成单音切割，因此，论文提出的一种新的音符音高划分方法，在基于一般能量划分的基础上，采用基于倍音列的音高识别模型对划分结果进行二次划分、规整，最终实现哼唱音符音高的划分。实验表明，该划分方法能够有效地实现哼唱音符音高的准确划分。

Universal Method for the Prediction of Abrasive Waterjet Performance in Mining

Abrasive waterjets （AWJs） can be used in extreme mining conditions for hard rock destruction, due to their ability to effectively cut difficult-to-machine materials with an absence of dust formation. They can also be used for explosion, intrinsic, and fire safety. Every destructible material can be considered as either ductile or brittle in terms of its fracture mechanics. Thus, there is a need for a method to predict the efficiency of cutting with AWJs that is highly accurate irrespective of material. This problem can be solved using the energy conservation approach, which states the proportionality between the material removal volume and the kinetic energy of AWJs. This paper describes a method based on this approach, along with recommendations on reaching the most effective level of destruction. Recommendations are provided regarding rational ranges of values for the relation of abrasive flow rate to water flow rate, standoff distance, and size of abrasive particles. I also provide a parameter to establish the threshold conditions for a material＇s destruction initiation based on the temporary-structural approach of fracture mechanics.

基于355nm紫外激光切割柔性覆铜板的工艺参数优化

针对紫外激光切割柔性覆铜板时出现焦黑碳化、过熔及过多能量损耗等问题,采用355 nm紫外纳秒激光切割机对49μm厚聚酰亚胺双面无胶柔性覆铜板进行激光切割实验,通过预切割遍历参数以验证切割覆铜板的最小能量——临界切割能量。在此基础上,研究了切割参数对柔性覆铜板表面形貌、截面形貌、碳化程度、刻缝宽度以及表面和截面成分变化的影响。实验结果表明:激光切割速度、切割功率和重复切割次数对柔性覆铜板的切割质量具有重要影响,提升切割速度、保持适中的切割功率、降低重复切割次数能够获得切口光滑且无积碳的高质量、低功耗切割效果。由以上结果可得出本实验条件下的最佳工艺参数:切割速度为2000 mm/s,切割功率为12 W,重复切割次数为70次。本实验研究结果为实现柔性覆铜板的高质量、低能耗激光切割提供了工艺依据,而且该切割工艺可适用于柔性电路板、聚酰亚胺覆盖膜及补强板等通过激光切割成形的材料。

Bidirectional secondary transmissions with energy harvesting in cognitive wireless sensor networks

To the existing spectrum sharing schemes in wireless-powered cognitive wireless sensor networks,the protocols are limited to either separate the primary and the secondary transmission or allow the secondary user to transmit signals in a time slot when it forwards the primary signal.In order to address this limitation,a novel cooperative spectrum sharing scheme is proposed,where the secondary transmission is multiplexed with both the primary transmission and the relay transmission.Specifically,the process of transmission is on a three-phase time-switching relaying basis.In the first phase,a cognitive sensor node SU1 scavenges energy from the primary transmission.In the second phase,another sensor node SU2 and primary transmitter simultaneously transmit signals to the SU1.In the third phase,the node SU1 can assist the primary transmission to acquire the opportunity of spectrum sharing.Joint decoding and interference cancellation technique is adopted at the receivers to retrieve the desired signals.We further derive the closed-form expressions for the outage probabilities of both the primary and secondary systems.Moreover,we address optimization of energy harvesting duration and power allocation coefficient strategy under performance criteria.An effective algorithm is then presented to solve the optimization problem.Simulation results demonstrate that with the optimized solutions,the sensor nodes with the proposed cooperative spectrum sharing scheme can utilize the spectrum in a more efficient manner without deteriorating the performance of the primary transmission,as compared with the existing one-directional scheme in the literature.

Modeling of Transient Thermal Conditions in Cutting

The thermal conditions like the temperature distribution and the heat fluxes during metal cutting have a major influence on the machinability, the tool lifetime, the metallurgical structure and thus the functionality of the work piece. This in particular applies for manufacturing processes like milling, drilling and turning for high-value turbomachinery components like impellers, combustion engines and compressors of the aerospace and automotive industry as well as energy generation, which play a major role in modern societies. However, numerous analytical and experimental efforts have been conducted in order to understand the thermal conditions in metal cutting, yet many questions still prevail. Most models are based on a stationary point of view and do not include time dependent effects like in intensity and distribution varying heat sources, varying engagement conditions and progressive tool wear. In order to cover such transient physics an analytical approach based on Green＇s functions for the solution of the partial differential equations of unsteady heat conduction in solids is used to model entire transient temperature fields. The validation of the model is carried out in orthogonal cutting experiments not only punctually but also for entire temperature fields. For these experiments an integrated measurement of prevailing cutting force and temperature fields in the tool and the chip by means of high-speed thermography were applied. The thermal images were analyzed with regard to thermodynamic energy balancing in order to derive the heat partition between tool, chips and workpiece. The thus calculated heat flow into the tool was subsequently used in order to analytically model the transient volumetric temperature fields in the tool. The described methodology enables the modeling of the transient thermal state in the cutting zone and particular in the tool, which is directly linked to phenomena like tool wear and workpiece surface modifications.

预浸料厚坯超声切割工艺研究

预浸料厚坯超声切割技术,具有无刀具磨损、加工速度快、加工精度高、无粉尘污染等优势,切割质量优异,在国外已得到了广泛应用,而国内目前仍处于初期研究阶段。本文以航空航天应用为主的碳纤维预浸料厚坯为实验材料,研究了切割温度、切割速度以及切割能量等切割工艺参数对切割质量的影响。研究结果表明,对于一定厚度的预浸料厚坯,最优的切割工艺参数组合:切割温度为5℃,切割速度为1.0m/min,切割能量为8级。该研究方法与研究成果为超声切割技术在预浸料切割中的应用奠定了基础。