Papers by Keyword: Toughness

Abstract: Two kinds of polymer fiber and polymer latex are used to improve the toughness and bondability of cement mortar. The influences of the fiber and latex on the compressive and flexural strength, compressive strength-flexural strength ratio (CS/FS), bond flexural strength and compactedness of the hardened mortar were studied. The results showed that both of the latex and fibre can improve the compressive and flexural strength of mortar in low content, decrease the CS/FS, and then improve the toughness significantly. The bond flexural strength of mortar can be improved by 40-50% when the latex is added. The effect of fibre-latex added together was better than that of two matters added separately. The optimized components for Fibre-Latex hybrid were: 0.28% of PVA+5% of ACE.

Abstract: Reactive powder concrete (RPC) containing blast furnace slag prepared for hydraulic structure with a designed strength of 150 MPa is examined. We first investigate mixture proportions of RPC to fit the strength requirement, and then, concentrate on the material with 50% replacement of silica fume by blast furnace slag to study seismic resistant properties. Results indicate that curing process and steel fiber can enhance the compressive strength, flexural strength, shear strength and fracture toughness. With 210°C curing, flexural strength of RPC containing 2% steel fibers reaches 91 MPa, almost three times without the fibers. Meanwhile, the shear strength is 47.8 MPa. Dynamic stress-strain curves determined by SHPB test display that the compressive strength of RPC increases with increasing applied strain rate. Applied strain rate dominates the stress-strain behavior and fracture energy of RPC. Toughness index of RPC is improved powerfully by adding a few steel fibers. The fracture toughness of RPC with 50% slag replacement comes to 1.08 MPa·m^1/2, and reaches 2.67 MPa·m^1/2 as 2% steel fibers are added.

Abstract: In order to improve toughness of the weld heat affected zone (HAZ) of ultra-fine grained (UFG) steel, a thermal simulation procedure of Fe-Mn-Si UFG steels with different Al addition was conducted and the corresponding microstructure was characterized and investigated. The results indicate that the maximum value on driving force of nucleation is ultra-fine grain steel with wtAl=0.6%, it has been explained in Nucleation kinetics that the grains are fine in UFG2. On the other hand, the bainite ferrite growth orientation has been increased. The toughness was remarkably enhanced in the steel welded heat affected zone. The formation of strie retained austenite and grain refinement of bainite ferrite in Fe-Mn-Si UFG steels with Al additions results in the increasing toughness of weld HAZ.

Abstract: Two kinds of magnetron sputtering ZrAlN films containing 23%atAl were deposited. The first was multicomponent ZrAlN film, the second was structure gradient and mulilayer film, named superlattice ZrAlN film. The microstructure was studied by FESEM, TEM , XRD, its mechanical properties were evaluated by nano-indentation method. The fracture toughness of films were determined from the length of ‘radial cracks’ on the applied diamond identer load 1.96N. the results show that, multicomponent ZrAlN film has hardness value of 35GPa, fracutre toughness value of 1.97MPa·m^-0.5; while superlattice ZrAlN film has coresponding value of 40.1GPa and 3.17MPa·m^-0.5. TEM image illustrates the superlattice ZrAlN film period is 2.5nm, nanoidentation test shows superlattice film has higher elastic recovery parameter and lower plastic work.

Abstract: Through adding enough calcium to C-Mn steel, the second phase particles of CaO can be found in C-Mn steel. The microstructure, the grain size and the toughness of CGHAZ in micro-calcium steel and no micro-calcium steel were studied by TEM, SEM and series impact experiment. The research shows that: the second phase particles CaO in micro-calcium steel have strong pinning force to grain boundary of CGHAZ; the second phase particles can retard grain growth in the course of welding in micro-calcium steel, fining grain at CGHAZ and improving the toughness of CGHAZ in micro-calcium steel.

Abstract: The anisotropy of tensile properties and charpy impact fracture toughness and its relationship with UOE pipe forming has been study on X80 micro alloy steel. All samples selected from 90^º and 180^º of pipes in transverse and longitudinal orientations after UOE forming. The steel was supplied as a hot rolled plate with accelerated cooling. Microstructure of the micro alloy steel was various combinations of acicular ferrite, granular ferrite and M/A phases. Charpy impact fracture toughness tests were carried out in -50 °C to 0 °C. Minimum and maximum yield strength appears in the 180^º and 90^º of pipe in longitudinal and transverse orientations respectively. Increasing in the yield strength related to minimum amount was about 5.8 % after UOE forming. Comparison between yield strength after and before forming appears increased about 6.9 % due to forming. With decreasing in the test temperature from -50 °C to 0 °C, fracture energy decrease up to 0.9 % that it’s very little and relinquishment. However for samples that fractured in the temperature of -50 °C difference between highest and lowest energy was about 5.9 %. Charpy test results appear that fine M/A phase not a major factor on decrease of upper shelf energy, if homogenize distributed in the acicular ferrite matrix.

Abstract: This intends to examine the flexural behavioral characteristics of hybrid UHPC using a mix of steel fibers with different lengths. Three types of fibers are adopted with fixed diameter of 0.2 mm and lengths of 13, 16.3 and 19.5 mm (aspect ratio of 65, 82 and 98, respectively). Comparative analysis of the flexural strength, load bearing capacity, deflection and toughness is performed adopting a mix use of these 3 types of steel fibers with ratio of 2% and 1.5%. The results show that the hybrid use of steel fibers improves significantly the flexural strength and flexural toughness compared to the use of a single type of fiber. When steel fibers with lengths of 16.3 mm and 19.5mm are admixed at a rate of 1% each, UHPC develops a flexural strength larger by 27% (maximum 50%) than conventional UHPC admixed with 2% of steel fiber with length of 13 mm. Moreover, flexural strength similar to that of conventional UHPC is secured when steel fibers with lengths of 16.3 mm and 19.5mm are admixed at respective rates of 0.5% and 1% (total rate of 1.5%).

Abstract: Surface degradation and cracking of dense hydroxyapatite were evaluated through Vickers micro indentation using indentation loads ranged from 25 gf to 2000 gf. Crack lengths, imprint diameters and the number of lateral cracks and chips were measured using SEM. The crack length-indentation load data were analyzed with regard to the specific relations of Palmqvist and fully developed radial cracks. Crack type transition load from Palmqvist to median crack was experimentally assessed through serial sectioning technique. The analytical estimated transition load, based on the theoretical relation of the indentation load and crack lengths showed a good agreement with one obtained from experimental itinerary. Palmqvist and median cracks were identified in low and medium indentation loads, respectively. High indentation load could also lead to the formation of lateral cracks and chips. The tendency for lateral cracking was evaluated taking into account the number of lateral cracks and chips. The chips were found to be appeared just after test in higher indentation load, whereas in medium loads they could be detectable only after several weeks.

Abstract: During the mid 1990s earthquakes in Northridge, California, and Kobe, Japan, illustrated a lack of understanding of the behaviour of structural steels exposed to seismic loads. Under this type of load regime, structural steel members are subjected to fully plastic load cycles and unexpectedly brittle failures resulted. This paper presents a simple, yet powerful, method for predicting the accumulation of damage in a steel element, based on its toughness. In addition the damage parameter chosen provides an accurate prediction of when failure of the element can be expected to occur. The damage accumulation model developed allows for the deconvolution of complex load histories, such as could be expected to occur during a seismic event, in a systematic, stepwise manner. This approach is ideally suited to automation and could readily be implemented into a finite element model.

Abstract: HVOF coating finds application in industry to protect the surface from the harsh environments such as high temperature, corrosion, and abrasion. In the present study, HVOF coating consisting of Inconel 625 powders blended with WC particles and sprayed on to 304 steel is carried out. The mechanical properties, such as elastic modules and fracture toughness, of the resulting coating are determined using the indentation tests. The influence of the mass fraction of WC on the fracture toughness and elastic modulus of the coating are also examined. It is found that addition of WC particles in Inconel 625 powder enhances the fracture toughness of the resulting surface. This is attributed to increased elastic modules and hardness.