The influence of imperfect bonding, owing to partial lack of adhesive, on the strength of composite non-crimp fabric (NCF) double-lap shear (DLS) joints was experimentally and numerically ...investigated. Fabrics were layered and compacted using a thermoplastic veil while infiltration of the preforms was done using the vacuum assisted process. Paste adhesive bonding was carried out by implementing the novel insertion squeeze flow process. Quality of adhesive bonding was tested using X-ray imaging and ultrasonic C-scan inspection. The tensile lap shear strength of the DLS joints was determined experimentally. Digital macrographs revealed that the specimens failed due to shear failure of the adhesive (debonding) and fracture of the composite boundary layer. As a second approach, a mesomechanical model based on the FE method and the (homogenized) progressive failure analysis method was developed. In the model, the areas without adhesion, as detected by the C-scans, were included. Numerical simulations of failure initiation and progression at the NCF joint and the adhesive indicated that it is possible to predict the strength and failure mechanisms of the imperfect bonded DLS joints.
This paper investigates and provides experimental evidence of the bond characteristics between carbon fibre reinforced polymer (CFRP) and steel plates under elevated temperature exposures. A series ...of tensile tests was carried out on CFRP/steel plates specimens joined together in double-lap shear joints and subjected to a range of environmental temperatures between 20 °C up to 60 °C, which would be usually encountered in civil infrastructure applications. High modulus (640 GPa) unidirectional carbon fibre plies were used in wet lay-up fabrication method to strengthen the composite matrix. Three different epoxy resins were used for the fabrication of the CFRP/steel specimens. The objective of the current experimental work is to determine the ultimate strength, failure patterns, elongation development, and lap-shear stress and slip variation under those exposures. This will help in enhancing the competency of using CFRP in retrofitting steel structures at high-temperature environments, usually experienced in civil construction applications.
The present work focuses on simulation of nonlinear mechanical behaviors of adhesively bonded DLS (double lap shear) joints for variable extension rates and temperatures using the implicit ABAQUS ...solver. Load–displacement curves of DLS joints at nine combinations of extension rates and environmental temperatures are initially obtained by conducting tensile tests in a UTM. The joint specimens are made from dual phase (DP) steel coupons bonded with a rubber-toughened adhesive. It is shown that the shell–solid model of a DLS joint, in which substrates are modeled with shell elements and adhesive with solid elements, can effectively predict the mechanical behavior of the joint. Exponent Drucker-Prager or Von Mises yield criterion together with nonlinear isotropic hardening is used for the simulation of DLS joint tests. It has been found that at a low temperature (−20°C), both Von Mises and exponent Drucker-Prager criteria give close prediction of experimental load–extension curves. However, at a high temperature (82°C), Von Mises condition tends to yield a perceptibly softer joint behavior, while the corresponding response obtained using exponent Drucker-Prager criterion is much closer to the experimental load–displacement curve.
The goals of this two-phase experimental program were to optimize the effectiveness of an icephobic coating for use on several Space Shuttle surfaces. Coating application with a foam brush provided ...consistent, controlled and reproducible surface coverage. Ice samples were grown slowly and consistently at −10°C prior to cooling to a constant −112°C temperature for cryogenic double lap shear testing. Phase 1 tests were focused on finding an optimal coating mix of Rain-X and varying weight fractions of PTFE powders MP-55 and UF-8TA. The MP-55 coatings produced large reductions in ice adhesion to aluminum coupons while the UF-8TA coatings were similar to uncoated controls. The M4 mixture with 40% MP-55 and 60% Rain-X gave the best and most consistent coating with outstanding performance and durability through five cycles of ice growth and adhesion failure. Phase 2 tests verified the effectiveness and durability of this coating over Koropon, Kapton tape, Kapton film and fire-retardant-paint surfaces on the shuttle and quantified the changes in effectiveness resulting from the addition of an ultraviolet light absorber (UVA). Solvent loss from Rain-X during prolonged mixing of the coating caused a greater increase in ice adhesion than that by adding the UVA.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The brackets that secure the liquid oxygen feed line to the external tank are known locations of frost and ice growth during the pre-launch period following fuel loading. This experimental program ...quantified the reduction in adhesion that resulted when ice phobic coatings were applied to test coupons that simulated the bracket surface. Double lap shear testing of coated and uncoated coupons provided robust test specimens and consistent load response patterns with exceptional resolution. Ice was grown as strong and consistently as possible for these tests and then subjected to temperature decreases comparable to those of the bracket. All tests were conducted at a constant temperature of −
112 °C (−
170 °F) and included uncoated controls with each group of samples. The program evolved in three phases. Phase 1 evaluated a wide range of coatings, and showed that Rain-X mixed with MP-55 powdered Teflon (RXM) was an outstanding coating to reduce ice adhesion to Koropon coated aluminum. Coating material retained on the ice surface following each test indicated failure in the coating and the potential for loss of effectiveness with repeated ice formation and release. Phase 2 evaluated modifications to RXM that might enhance durability while maintaining effectiveness. However, the modified mixtures did not improve coating durability or ice release. Phase 3 focused on the effects of mixing method, cure time, wiping off of excess coating, and coating resistance to weathering by water. A progressive coating loss again occurred through repeat test cycles, but performance generally improved. Results also indicated that cure times longer than 1.5 h prior to coating disturbance are needed for optimal performance. The MP-55 remaining on coupon surfaces after 3 cycles of testing and on one untested coupon from the same group was measured with XPS. The tested coupons retained slightly less MP-55 than the untested coupon, confirming the loss of coating. Contact angle analysis of these same coupons showed that the hydrophobic performance of the tested surfaces was largely preserved. Scanning electron microscopy with an energy dispersive spectroscopy elemental map indicated that the MP-55 was evenly dispersed throughout the coated surface, and abrasive wiping did not remove a significant portion of the Teflon. Test results suggest follow-up studies to refine the optimal coating formulation, mixing and application procedures, and understanding of reaction processes, cure time, and coating durability. Double lap shear testing and XPS analysis can quantify ice adhesion and coating profile thickness changes with cycling, and is capable of resolving these remaining issues.
Steel-concrete composite slabs have been used for bridge deck construction in Japan because of several advantages, e.g., safety construction and high fatigue durability. On the other hand, these ...slabs may cause negative influences such as overweight, increasing costs and low constructability, due to many mechanical shear connectors. The quantities of shear connectors may be reduced by gluing steel-plate and concrete with a cementitious adhesive. The present study aims at examining shear bond strength and quantifying the dispersion of the strength. To investigate the dispersion, a double-lap shear test is conducted, in addition to a simple direct shear test, to examine surface treatment. A Monte Carlo Simulation using the Weibull distribution of the strength is performed to evaluate the effect of dispersion. The simulation implies that the shear stress due to the traffic load may be negligible, indicating the applicability of the composite system for highway bridge decks.
HYGROTHERMAL DURABILITY OF ADHESIVELY BONDED FRP/STEEL JOINTS Heshmati, Mohsen; Haghani, Reza; Al-Emrani, Mohammad
Proceedings of International Structural Engineering and Construction,
2015, Letnik:
2, Številka:
1
Journal Article, Conference Proceeding
Odprti dostop
The use of fiber reinforce polymer, FRP, bonding to strengthen and repair deteriorated steel structures is increasing owing to its unique advantages over traditional strengthening and repair ...techniques. However, the lack of knowledge regarding environmental durability of adhesively bonded FRP/steel joints still hinders the widespread application of this method in steel structures. A number of studies have reported significant degradation of mechanical properties of these joints in hot and wet environments. In addition to that, the mechanisms of failure have been observed empirically to change from cohesive failure in the adhesive to apparent interfacial failure with increasing amount of moisture. This study presents the results of an experimental and numerical investigation to predict the mechanical behavior of FRP/steel joints after hygrothermal aging. First, moisture diffusion kinetics and mechanical degradation of a two-part commercially available epoxy adhesive and Carbon FRP material were experimentally characterized over a wide range of temperature and humidity conditions. These parameters were then incorporated in a coupled 3D diffusion-mechanical finite element, FE, model. In addition, bonded double-lap shear joints of CFRP/steel were aged for up to a year and tested to failure. It is found that the presence of moisture for less than a critical period can increase the joint strength. However, prolonged exposure to the same moisture content degrades the load-carrying capacity of the joint.
This study examined the effects of 0.5 mass%Zn addition to a Sn-57 mass%Bi solder on the interfacial and mechanical properties of the solder joint with Cu substrate. The shear strength was measured ...by modified double lap shear joint model. Creep tests were performed at 10 MPa and 80°C. The shear stength of the solder/Cu joint was found to decrease with aging treatment. Rapid decrease in shear strength of the Sn-57 mass%Bi/Cu joint was noticed in the aged specimen. This seems to be caused by crack growth between a reaction layer and a Cu substrate. At the tension test after aging treatment, the failure of joint was dependent upon existence of crack in the intermetallic compound layer. When the crack existed in the intermetellic compound layer, fracture occurred at the interface of Cu and intermetallic compound. By Zn addition in the Sn-Bi system, the fracture occurred at the interface of the solder and the inermetallic compound. In the Sn-Bi system, however, the crack under creep test was popagated in the solder with regardless existence of crack in the intermetallic compound. In the Sn-Bi-Zn system, the crack was popagated through the interface of the solder and the reaction layer.
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