Lamp with rigid LED strip - Design and thermal management
Investigations are connected with design and application of thermally and cost effective rigid LED strips. Standard FR 4 PCB is used for making rigid strip and LEDs are soldered on it. Special copper pins soldered underneath LEDs contribute to low thermal resistance between LEDs and heat sink - like when MCPCBs are used. Application of this type low cost rigid LED strips allows decreasing operations (and expenses) connected with assembling of LEDs onto a heat sink several times. A lamp for interior lighting is designed on the base of this type LED strips. Thermal management calculations are made and proper heat sink is chosen. Thermal loading of LEDs is experimentally tested at various ambient conditions (air temperatures from 20°C to 45°C) and different current values through LEDs - up to 600 mA. Infrared thermography is used for evaluation of temperature distribution on LEDs and heat sink. Thermal management investigations show very good qualities of developed LED strips.
LEDs' thermal management aided by infrared thermography
Investigation deals with LED's thermal management optimization in dependence of operating condition aided by application of infrared thermography. Thermal management calculations allow estimating temperature distribution on the LEDs, metal - core printed circuit boards (MCPCB) and heat sink but often real results may be different and experimental investigations are necessary. Good results are obtained using IR thermography with IR camera for the middle IR spectral region (8 – 13 µm). Application of infrared thermography allows obtaining temperature distribution at real operating conditions. Thermal images analyzing allow obtaining real temperature distribution on the LEDs, solder points and different areas on the heat sink at different operating conditions. Results of this investigation allow adjusting proper LEDs' regime of operation in lighting system with maximum light output in dependence of ambient temperature conditions and to ensure long life (over 50000 hours) of the LEDs.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.