This paper proposes a methodology for the prediction of ductile fracture observed in steel specimens during tension tests at elevated temperatures. This methodology consists of two steps. First, true ...stress–strain curves that include the post-necking response are developed at both ambient and elevated temperatures. Second, a stress-modified critical strain (SMCS) fracture model is calibrated and utilized to model the ductile fracture behavior of structural steels exposed to elevated temperatures. Development of true stress–strain curves and calibration of SMCS fracture model parameters are based on the tension tests data of ASTM A992 steel tension specimen together with the simulation results of the tested tension specimens in Abaqus at elevated temperatures. The developed true stress–strain curves and fracture model parameters are further validated against the additional test results of ASTM A992 steel in tension that were not used in the calibration of the fracture models. Sensitivity analysis on fracture prediction considering the effect of the mesh size and the variation of fracture model parameters are investigated. The analysis results suggest that the predicted fracture initiation strain is mildly sensitive to the effect of mesh size and variation of fracture model parameters. The robustness and limitations of the proposed methodology in predicting ductile fracture at elevated temperatures were further investigated. Overall, the developed methodology for ductile fracture in tensile specimens of ASTM A992 steel was demonstrated to reasonably predict tensile fracture at temperatures up to 1000°C.
In this work, the aged refuse (AR) excavated from a typical refuse landfill with over 10 years of placement was used for the enhancement of bio-hydrogen production from food wastes. Firstly, the food ...wastes taken from a university dining hall were inoculated with sewage sludge (SL) pre-treated by 15
min heating at 80
°C. It was found that below 0.4% of hydrogen concentration could be detected in the biogas produced due to its severe acidification properties. However, the addition of AR (50% in weight) can considerably increase the hydrogen concentration in the biogas to over 26.6% with pH ascending from 4.36 to 5.81, in comparison with 4–6% using activated carbon as additive with pH descending from 4.43 to 3.91. Meanwhile, it was also found that the hydrogen content in the biogas decreased drastically to 3.3% when the AR was sterilized by heating at 160
°C for 2
h and then used as additive for bio-hydrogen production from food wastes, indicating that the AR may chiefly function as a microbial inoculum instead of a porous material like activated carbon. Statistical analysis showed that the ultimate hydrogen production potential (
H
p), hydrogen production rate (
R
max) and lag-phase time (
λ) were found to be 193.85
mL/gVS, 94.35
mL/(h
gVS), 15.28
h, respectively, in the presence of 50% AR, and the optimal mixing ratios were 100:50 (wet weight) for food wastes to AR and 100:30 (dry weight) for food wastes to sewage SL, respectively.
A novel three-port converter (TPC) is proposed to meet the diversity of demand for electrical equipment in this paper. It interfaces a single input power port and two output ports. The proposed TPC ...can be viewed as two bidirectional DC-DC converters. With a different operation mode, the proposed TPC can output two DC voltages or a single DC and a single AC voltage. The topology and operation principal of the TPC is analyzed in detail. Moreover, the mathematic model of the TPC is derived. Then, by considering the dynamic response and disturbance suppression, a step by step PI and PR controller design process for TPC is also presented. Both the simulation and the experimental results validate the proposed method.
•Cyclic loading experiments on Q690 high strength steel beam-columns were conducted.•The hysteretic behavior, energy dissipation and failure modes were analyzed.•Damage-based hysteretic models for ...Q690 high strength steel beam-columns were calibrated.
Q690 high strength steel (HSS) is a structural steel with yield-to-tensile ratio being generally greater than 0.90 and elongation lower than 20%, resulting in considerable decrease in steel member ductility. In seismic affecting zones, steel members are usually designed as compact sections to avoid premature local buckling for attaining fully developed plasticity. However, this approach increases the potential risk of fracture for Q690 steel structures. Thus, cyclic behaviors of Q690D HSS compact section beam-columns need to be thoroughly investigated. To this end, this paper conducted five cyclic loading tests of Q690 HSS compact H-section beam-columns based on a reliable testing system. The influences of the flange width-to-thickness ratio, web height-to-thickness ratio, axial-load ratio and overall slenderness on the failure mode, energy dissipation capacity and hysteretic behavior were analyzed. It shows that plastic local buckling dominates the failure mechanism of all the specimens without overall buckling being observed. The ultimate inter-story drift ratio was more than 1/50. The Q690 welded beam-columns with Class 1 and Class 2 H-section exhibit not only favorable plastic deformability but also excellent energy dissipation capacity and therefore could be applied in seismic steel frames. To attain accurate evaluation of damage and cyclic response, two damage models and two point-oriented hysteretic models were selected and combined to form four damage-based hysteretic models. The four hysteretic models were then implemented to simulate the cyclic loading experiments. It was found that the ultimate strength-oriented hysteretic model incorporated with Kumar Satish damage model provides the most accurate simulation. The hysteretic model parameters were calibrated using experiments data. The simulation results of the developed hysteretic model match well with those experimental curves.
Aiming at improved electrical conductive performance and simultaneously enhanced mechanical properties, a novel segregated structure was constructed for poly(ethylene-
co
-octene) (POE)/multi-walled ...carbon nanotube (MWCNT) elastomeric conductive composites with chemically cross-linked POE granules. Structural examination revealed the formation of unique phase morphologies with a stable segregated structure, in which the uncross-linked POE/MWCNT phase localized out of the cross-linked granules. With such a novel segregated structure, a percolation threshold as low as 1.5 vol% of MWCNTs was observed, which is significantly lower than the melt compounded POE/MWCNT composites; the stress at 100% and 300% stretching increased for more than 12% and 30%, respectively, and the tensile modulus inherent to the matrix elastomer was maintained. The elastic recovery of the composite with such a novel segregated structure was more than 85% and 65% after large strains up to 100% and 300%, respectively, always higher than the melt compounded POE/MWCNT composites. The Shore A hardness of the elastomeric conductive composites with cross-linked POE granules was also lower, showing better elasticity of POE/MWCNT composites with such a novel segregated structure. All these results demonstrated that the elastomeric POE/MWCNT conductive composites with such a novel segregated structure exhibited greatly reduced percolation thresholds with enhancement in mechanical properties, which provides a new way for the preparation of elastomeric conductive composites with simultaneously improved electrical performance and mechanical properties.
As a product of a multistep enzymatic reaction, accumulation of poly(3-hydroxybutyrate) (PHB) in Escherichia coli (E. coli) can be achieved by overexpression of the PHB synthesis pathway from a ...native producer involving three genes phbC, phbA, and phbB. Pathway optimization by adjusting expression levels of the three genes can influence properties of the final product. Here, we reported a semirational approach for highly efficient PHB pathway optimization in E. coli based on a phbCAB operon cloned from the native producer Ralstonia entropha (R. entropha). Rationally designed ribosomal binding site (RBS) libraries with defined strengths for each of the three genes were constructed based on high or low copy number plasmids in a one-pot reaction by an oligo-linker mediated assembly (OLMA) method. Strains with desired properties were evaluated and selected by three different methodologies, including visual selection, high-throughput screening, and detailed in-depth analysis. Applying this approach, strains accumulating 0%–92% PHB contents in cell dry weight (CDW) were achieved. PHB with various weight-average molecular weights (M w ) of 2.7–6.8 × 106 were also efficiently produced in relatively high contents. These results suggest that the semirational approach combining library design, construction, and proper screening is an efficient way to optimize PHB and other multienzyme pathways.
•Both numerical and theoretical creep buckling analyses are performed on high-strength steel columns.•The creep buckling behavior of steel columns is affected by several key variables, including ...slenderness ratio, temperature level, and material strength.•A theoretical approach is proposed to determine the creep buckling load for high-strength steel columns.•Based on EN 1993-1-2, a modification factor of the creep buckling load for high-strength steel columns is proposed.
Under fire conditions, the fire resistance of steel columns may be critically affected by steel creep. However, in the current codes of practice, creep effect has not been explicitly considered in determination of the high-temperature load-bearing capacity of steel columns. This may result in unsafe predictions of the load-bearing capacity of steel columns exposed to fire. In this study, both numerical and theoretical approaches are employed to study the creep effect on the critical strength of Chinese grades Q550, Q690, and Q890 high-strength steel columns. First, the creep buckling behavior of steel columns is numerically studied using the finite element program ABAQUS, and then validated against the existing experimental results. The creep buckling load factor, which is the ratio of the buckling load with creep effect to that without creep effect, is calibrated from the numerical approach and plotted against creep buckling time. The creep buckling load factor vs. buckling time curves are also established from the theoretical approach and compared with the curves established from tests and numerical analyses. A parametric study is then conducted by using a validated theoretical approach to investigate the effects of several variables including slenderness ratio, temperature, and material strength on the creep buckling load of high-strength steel columns. Based on the parametric study results together with current code of practice EN 1993-1-2, the modification factors of the buckling load with creep effect are proposed. The results demonstrate that under fire conditions without considering the creep effect, the buckling load of high-strength steel columns may be overestimated.
Blind-bolts offer a feasible way for connecting a steel member with closed-hollow section to a member with open-section. However, the relatively higher cost of the available blind-bolts is an ...obstacle to practical application. For reducing the production cost, a modified Hollo-Bolt with standardized slotted sleeves (MBB) was proposed. To investigate the load-resisting behavior of the proposed MBB and conduct comparative studies with the normal blind-bolt (NBB), extensive experimental tests under pure tension and shear were performed on NBB and MBB of three different diameters and two common strength grades. The results indicate that MBBs and NBBs showed similar load-resisting behavior under tension as the fracture strength of the bolt shank solely controlled the ultimate tension-resisting capacity of the blind-bolt unit. Under simple shear, however, the load-resisting capacity of MBBs was slightly lower than that of NBBs due to the relatively shorter embedment length of its unslotted tube. Nonetheless, the load-resisting capacities of both MBBs and NBBs under simple shear were significantly higher than those of common high strength bolts, owing to contributions from the sleeve and unslotted tube. Moreover, finite element models incorporating ductile fracture criterion were established to replicate the load-resisting behavior of the blind-bolts under tested scenarios. It was revealed that the differences in the shear resistance of NBB and MBB were mainly attributable to the significant tensile stress of the bolt shank and the delayed damage of unslotted tube, which is essentially related to the embedment length of unslotted tube.
•A modified blind bolt with standardized slotted sleeve (SBB) is proposed.•Experimental studies on SBB and the companion normal blind bolt (NBB) are conducted.•SBB showed similar load-resisting capacity as NBB under direct tension.•The shear-resisting capacity of SBB was slightly smaller than that of NBB•Numerical models considering fracture behavior are established and validated.
Tin selenite (SnSe) has attracted significant attention due to its record thermoelectric figure of merit (ZT=2.6 at 923 K) of its single crystal. However, the polycrystalline SnSe processes ...considerably less ZTs (els1.1). In this study, we investigate the thermoelectric properties of Ag-doped polycrystalline SnSe, which was synthesized via zone melting and hot pressing. By comparing our results and previous reports of Ag-doped single crystals and polycrystals, we determine that the high texturing degree is essential for achieving good thermoelectric performance in polycrystalline SnSe. The zone-melted Sn0.99 Ag0.02 Se shows better thermoelectric performance than the Ag-doped SnSe single crystal in the entire temperature range, exhibiting a peak ZT of 1.3 at 793 K.
PDF