钢筋连接套简表面开裂分析

某套筒生产厂所产套筒在试验过程中有开裂现象,本文通过目视、金相、力学、扫描电镜等多项手段对失效试样及合格试样进行对比分析,得出与厂家不同的结论,即表面开裂的主要原因并非表面韧性不足,而是心部强度过低。     

Comparison of different failure criteria for fiber-reinforced plastics in terms of fracture curves for arbitrary stress combinations

For fiber-reinforced plastics exists a big number of different criteria for the failure prediction. The intention of this paper is to compare the TSAI-HIL-, the LaRC04- and PUCK’s criterion in terms of their fracture curves for a unidirectional glass-fiber reinforced composite layer. Therefore after the implementation of these three criteria, the two-dimensional fracture curves for all possible stress combinations, which can be derived from a general spatial stress tensor, are computed. In this way, the characteristics of the criteria, similarities and differences and possible weak points become obvious.     

On deformation and tearing of stiffened and un-stiffened square plates subjected to underwater explosion—a numerical study

In modern combat operations warships can be subjected to underwater blast loads capable of causing considerable structural damage. Research in the field of underwater explosion effects on structures has seen systematic developments since world war-I (WW-I) with the increased awareness that the possible underwater explosions and threats from the hunter killer “U” boats could now be countered. Most of the earlier investigations were conducted by military and these were classified. Cole [1] established empirical relations to model the underwater explosion (UNDEX) loading, which were the outcome of numerous experimental investigations done by the military agencies. In the present study the UNDEX load profile has been modeled as an exponentially decaying shock wave, which varies spatially and transiently. The failure modes in high strength (HS) and WELDOX Steel rectangular plates was predicted using an elasto-plastic model with isotropic hardening, strain rate effects and fracture criterion under clamped edge conditions. These models were implemented in the nonlinear finite element code ABAQUS/Explicit. The present study predicts and establishes the failure modes using a 3D FE analysis.     

Simulation of the climate system performance of a museum in case of failure events

The paper presents the evaluation of the current HVAC components and indoor climate of a high tech Naval Depot when the system fails. The methodology of the research was: first, implementation of the heat, air & moisture models of the building and HVAC components. Second, validation of the models using measured data from the existing building control system. Third, simulation of the current and new HVAC systems designs. Fourth, discussion of the usability of the approach. For this specific case, we concluded that the current system design performs well if, in case of a fault, the air supply to the depots is switched off automatically. The construction of the depots has sufficient thermal inertia to maintain a stable indoor climate for a period long enough to allow it to be repaired. The design could be further improved by controlling the indoor climate surrounding the depots instead of inside the depots itself. In such a case, even if the system did not detect a fault and continued supplying uncontrolled air to the surroundings of the depot, the indoor climate in the depot would remain stable. We conclude that the approach presented in this paper has a wider application than this single case study.     

Using Fuzzy Cost‐Based FMEA,GRA and Profitability Theory for Minimizing Failures at a Healthcare Diagnosis Service

This paper proposes an integrated approach to identify, evaluate and improve the potential failures in a service setting. This integrated approach combines Fuzzy cost‐based service‐specific FMEA (FCS‐FMEA), Grey Relational Analysis (GRA) and profitability theory for better prioritization of the service failures by considering cost as an important issue and using the profitability theory in a way that the corrective actions costs are taken into account. Considering profitability with FCS‐FMEA and GRA reduces the losses caused by failure occurrence. Besides, a maximization linear mathematical problem is used to select the best mix of failures to be repaired. We apply our approach to an academic example concerning the potential failures diagnosis of the Internal Medicine service of a hospital located in Seoul, Korea. We applied our approach and solved the associated maximization problem by a commercial solver, producing an optimal solution which indicates the most convenient mix of failures to be repaired by considering available budget. Copyright © 2013 John Wiley & Sons, Ltd.     

热应力作用下LNG储罐外罐裂缝及失效时间分析

对于大型液化天然气储罐,内罐泄漏时,由于内外表面温差产生的巨大热应力对于外罐裂缝开展及储罐失效有非常重要的影响。为了获得外罐裂缝的开展规律以及储罐失效时间以便指导实际工程的设计与维护,利用传热学与弹塑性力学相关理论,提出了一种应力叠加方法,近似计算在内罐泄漏时外罐出现裂缝的内外温差,并且结合数值模拟结果进行对比分析,验证理论方法的准确性,确定裂缝开展规律,最终求得内罐从最不利泄漏点开始泄漏到外罐内侧混凝土开裂的储罐失效时间。结果表明:①内罐泄漏时,热应力巨大,不可忽略,热应力和其他荷载共同作用导致外罐产生大量裂缝,裂缝首先在外罐顶部内表面产生,并迅速向外表面开展,最终贯穿罐顶,导致储罐失效;②首次求得了储罐从内罐开始泄漏到外罐产生裂缝的最小时间,在此时间内采取有力措施及时处理,对控制事故发展、避免发生严重灾害具有重要意义。     

Failure analysis on reflector blackening between lead frame electrodes in LEDs under WHTOL test

Blackening induced lumen decay in a QFN LED after WHTOL reliability test was reported and analyzed in this paper. A new LED blackening failure mechanism was proposed based on solid experimental results. We concluded that the failure process underwent delamination between lead frame and reflector polymer composites followed by chemical penetration, composite corrosion, silver migration, and finally caused blackening failure. Delamination and corrosive de-flash agent were the key factors for the failure mode. Besides, we also estimated the influence of the failure to the optical performance through simulation. Apart from other reported factors, this study highlighted that both composite corrosion and Ag migration could generate serious illumination decrease as well. The outcome of this study is valuable for LED manufacture and quality control in the future.     

基于SMP强度准则的预应力混凝土管桩的挤土效应分析

预应力混凝土管桩在沉桩过程中,将发生挤土效应和土塞效应,二者是有机统一的。基于SMP强度准则,考虑土塞效应,分析了预应力混凝土管桩的挤土效应及土塞效应,并推导了预应力混凝土管桩的应力场及位移场的计算公式。通过实例表明,基于考虑中间主应力的SMP强度准则推导得到的预应力混凝土管桩的应力状态及位移场的计算公式,在实际工程中具有一定的现实指导意义。     

同塔多回输电线路杆塔可靠指标及失效概率分析

输电线路杆塔结构可靠指标及失效概率的分析研究,目前已经广泛应用于实际工程当中,本文着重研究了500kV同塔四回输电线路杆塔的可靠指标及失效概率。对于风荷载占控制因素的杆塔结构,本文研究了可靠指标计算参数组合对于杆塔失效概率的影响,同时计算了500kV同塔四回典型杆塔的可靠指标及失效概率,提出基于输电杆塔可靠度理论的杆塔风险规避的建议。     

Influence of surface treatments on topography and bond strength of densely-sintered zirconium-oxide ceramic

The aim of this study was to evaluate the effect of surface treatments on the roughness and bond strength of dental materials containing MDP to zirconium oxide ceramic. Forty square-shaped zirconium-oxide ceramic blocks (Lava Zirconia, 3M-ESPE) were treated as follows: (CT) polished only; (SB) sandblasting (110 µm aluminum oxide particles) or (SC) silica coating (110 µm particles). Roughness of treated surface was measured using a profilometer (Ra) and by atomic force microscope (AFM). Two resin luting agents were used after silane application: self-adhesive (Rely X U200, 3M-ESPE) and dual cure (Rely X Ultimate, 3M-ESPE). The samples were submitted to microshear bond strength test. The failure analysis was performed. Data were submitted to ANOVA and Tukey test (α=0.05). Bond strength results ranged from 20.44 (CT+Ultimate) to 34.37 MPa (SC+U200) after 24 h and from 12.03 (CT+Ultimate) to 27.44 MPa (SC+U200) after 12 months of storage with SC statistically superior to the other treatments. Mean values of roughness varied from 0.07 (CT) to 0.85 µm (SC). The both resin luting agents showed similar results to all surface treatment groups. Silica coating provided the best treatment of the ceramic surface.