Microstructure And Mechanical Properites Of Welded Advanced Materials For Automotive Applications

Growing use of advanced materials (advanced high strength steel DP980 and ultralight-weight magnesium alloys) and innovative joining techniques (new-generation laser welding technology and weld bonding technique) is crucial for better fuel economy and lower CO2 emissions in automotive manufacturing. Microstructures and mechanical properties of fiber laser welded high strength low alloy and DP980 steel joints, weld-bonded Mg/Mg and Mg/steel joints and adhesive-bonded Mg/Mg joints were studied. Tempered martensite and welding concavity were observed in fiber laser welded DP980 joints which reduced fatigue resistance, while both HSLA and DP980 joints showed a superior tensile strength. Weld-bonded Mg/Mg and Mg/steel joints with an adhesive layer were significantly stronger than resistance spot welded Mg/steel joints. Reducing bonding length on weld bonded Mg/Mg joints led to a higher maximum tensile shear stress, both tensile and fatigue strength were slight lower than that of adhesive bonded Mg/Mg joints, while ability of energy absorption was equivalent. The tensile properties reduced at a higher temperature (90°C) but it increased at a lower temperature (-40°C).

Microstructure And Mechanical Properites Of Welded Advanced Materials For Automotive Applications

Growing use of advanced materials (advanced high strength steel DP980 and ultralight-weight magnesium alloys) and innovative joining techniques (new-generation laser welding technology and weld bonding technique) is crucial for better fuel economy and lower CO2 emissions in automotive manufacturing. Microstructures and mechanical properties of fiber laser welded high strength low alloy and DP980 steel joints, weld-bonded Mg/Mg and Mg/steel joints and adhesive-bonded Mg/Mg joints were studied. Tempered martensite and welding concavity were observed in fiber laser welded DP980 joints which reduced fatigue resistance, while both HSLA and DP980 joints showed a superior tensile strength. Weld-bonded Mg/Mg and Mg/steel joints with an adhesive layer were significantly stronger than resistance spot welded Mg/steel joints. Reducing bonding length on weld bonded Mg/Mg joints led to a higher maximum tensile shear stress, both tensile and fatigue strength were slight lower than that of adhesive bonded Mg/Mg joints, while ability of energy absorption was equivalent. The tensile properties reduced at a higher temperature (90°C) but it increased at a lower temperature (-40°C).

Interface Bonding Behavior of Concrete-Filled Steel Tube Blended with Circulating Fluidized Bed Bottom Ash

The interface bonding behavior between the steel tube and the concrete of concrete-filled steel tube (CFST) blended with circulating fluidized bed bottom ash (CFB-BA) was investigated in this study. A total of 8 groups of CFSTs stub columns were prepared with different dosage of CFB-BA, water-binder ratio (W/B), and interface bonding length. A series of push-out tests were carried out to acquire the data representing the interface bonding behavior. The results show that the dosage of CFB-BA has a direct effect on interface bonding behavior of CFST. CFB-BA can improve the interface bonding behavior of CFST. The highest ultimate bonding load and strength are achieved when the dosage of CFB-BA is 30%. When the dosage of CFB-BA increases to 50%, its interface bonding behavior decreases, but is still better than that of CFST without CFB-BA. W/B has a negative correlation with the interface bonding behavior of CFST. While the W/B increases, the interface bonding load and strength of CFST decreases. The increase of the interface bonding length can improve the interface bonding load, but cannot improve the interface bonding strength.

Effect of anchorage number and CFRP strips length on behavior of strengthened glulam timber beam for flexural loading

Laminated wooden beams are more preferred in the production of wooden structures than solid timber beams because they have a higher load-carrying capacity and allow larger openings to be used in the structure. The widespread use of wooden structures and the increasing size of the structures have revealed the need for strengthened laminated wooden beams and increase their ultimate load capacity. It has become necessary to develop reinforcement details to increase the ultimate load capacity of laminated wooden beams in wooden railroads or highway bridge beams, where the traffic load increases, especially in large wooden structures, in cases where large openings must be passed. Within the horizon of the study, the behavior and performance of three-layer glulam wooden beams strengthened with anchorage and non-anchorage CFRP strips with different bonding length under flexural loading were investigated experimentally. The three-point bending test was applied to glulam timber beam test specimens produced by laminating yellow pine wood material using the polyurethane adhesive. General load-displacement behaviors, ultimate load capacity, initial stiffness, displacement ductility ratios, and energy dissipation capacities were obtained. The increase in the bonding length of the CFRP strips used for strengthening in the glulam timber beam specimens and the use of CFRP fan type anchors at the strip ends increased the ultimate load capacity and initial stiffness values of the wooden beams, as well as the displacement ductility ratios and energy dissipation capacity values.

Calculation Method of Bonding Section of Joint Surface of Dangerous Rock Mass Based on Amplitude Ratio

In this study, through an analysis of vibration response characteristics of joint surface stiffness on dangerous rock mass, the relationship formula between amplitude ratio of the dangerous rock mass to the bedrock and the length of the bonding section of the joint surface is determined. The stability of the rock mass can be evaluated by combining the formula with the existing rock-mass limit equilibrium theory. This study proposes the existence of a resonance bonding length for the dangerous rock mass. When the length of the bonding section reaches the resonance bonding length, the dangerous rock mass has the largest response to the bedrock vibration. The study found that when the length of the bonding section of the dangerous rock mass is longer than the resonance bonding length, the amplitude ratio increases with the decrease of the bonding section and increases with the increase of the vibration frequency of the bedrock. When the length of the bonding section of the dangerous rock body is shorter than the resonance bonding length, the amplitude ratio decreases with the decrease of the bonding section and decreases with the increase of the vibration frequency of the bedrock. Indoor experiments were conducted by collecting the vibration time-history curves of rock blocks and stone piers and performing analysis and calculation, which proved the accuracy of the analytical results. Through the amplitude ratio of the dangerous rock mass and the bedrock, the bonding length can be calculated. This method can improve the calculation accuracy of the stability coefficient K of the dangerous rock mass.

Strain Transfer Analysis for Surface Bonded Fiber Sensor Considering Temperature Influence

Strain transfer ratio is one of the key characteristics to determine the accuracy of sensors for strain measurement and structural health monitoring. This paper presented a theoretical study on the strain transfer ratio of optical fiber sensors, which is generally bonded on the surface of target structure by adhesives to measure strain or stress. Compared to the prior efforts where only one type of loads, either mechanical or thermal, is considered, this paper included both of them in the modeling of strain transfer ratio and derived a general analytical expression for their relationships. It has been found that the strain transfer ratio is not a constant in some cases but varies with the strain being measured. The work studied the characteristics of fiber optic sensor in two consecutive approaches: 1) A simplified 2-dimentional multi-layer analytical model was built to derive the expression of strain transfer ratio as a function of the structural and material properties; 2) a numerical model that considers the realistic 3-dimentional structure of the sensor installation scenario was established for validating the analytical model in different case studies. Simulation results have shown that the analytical model matches well with the behavior of strain transfer ratio estimated by the numerical model, with an error less than 1.35%. Based on the validated analytical model, the discussion was further extended to derive the lower limit of the bonding length of optical fiber sensors to satisfy the requirement of measurement accuracy.

Strain Transfer in Surface-Bonded Optical Fiber Sensors

Fiber optic sensors represent one of the most promising technologies for the monitoring of various engineering structures. A major challenge in the field is to analyze and predict the strain transfer to the fiber core reliably. Many authors developed analytical models of a coated optical fiber, assuming null strain at the ends of the bonding length. However, this configuration only partially reflects real experimental setups in which the cable structure can be more complex and the strains do not drastically reduce to zero. In this study, a novel strain transfer model for surface-bonded sensing cables with multilayered structure was developed. The analytical model was validated both experimentally and numerically, considering two surface-mounted cable prototypes with three different bonding lengths and five load cases. The results demonstrated the capability of the model to predict the strain profile and, differently from the available strain transfer models, that the strain values at the extremities of the bonded fiber length are not null.

Some Considerations about the Effects of the Bonding Length on the Effectiveness of Spike Anchors in CFRP Reinforcements of Masonry

The main results of an experimental program concerning masonry pillars reinforced by CFRP strips (also provided by spike anchors) subjected to single lap shear tests are described in this paper. The experimental results, also compared with a previous experimental program, allowed to analyze the increment of bearing capacity produced by spike anchors to CFRP sheets having different bonding length.

Durability of Functionalized Carbon Structures with Optical Fiber Sensors in a Highly Alkaline Concrete Environment

The paper presents an investigation into the durability of functionalized carbon structures (FCS) in a highly alkaline concrete environment. First, the suitability of optical fibers with different coatings—i.e., acrylate, polyimide, or carbon—for the FCS was investigated by subjecting fibers with different coatings to micro/macro bending and a 5% sodium hydroxide (NaOH) (pH 14) solution. Then, the complete FCS was also subjected to a 5% NaOH solution. Finally, the effects of spatial variation of the fiber embedded in the FCS and the bonding strength between the fiber and FCS was evaluated using different configurations —i.e., fiber integrated into FCS in a straight line and/or with offsets. All three coatings passed the micro/macro bending tests and show degradation after alkaline exposure, with the carbon coating showing least degradation. The FCS showed relative stability after exposure to 5% NaOH. The optimum bonding length between the optical fiber and the carbon filament was found to be ≥150 mm for adequate sensitivity.