Double-lap Connection Research Articles

Calibration and validation of a 3D homogenised model to simulate the damage progression of pultruded GFRP composites

A damage progression failure model for tridimensional finite element (FE) analyses has recently been proposed, allowing the simulation of composites as homogenized materials, greatly reducing computational costs. It is able to predict the damage and post-failure behaviour of composites, while its calibration can be performed with data derived from the standardized experimental characterization of the composite materials. This paper presents the calibration of that model for 5 new glass-FRP pultruded profiles, followed by the simulation of different application/design cases: (i) wide compact tension; (ii) compact compression; (iii) web-crippling; and (iv) bolted double-lap connection tests. While the results show that further investigation is needed to address the experimental characterization of the in-plane shear properties and the numerical simulation of bearing failure, overall the models were well able to predict the experimental strength, post-failure behaviour, failure modes and damage patterns, showing that the feasibility of using this damage progression model as a design tool.

Preload loss of high-strength bolts in friction connections considering corrosion damage and fatigue loading

The preload loss of high-strength bolts in friction connections was investigated considering the corrosion damage and fatigue loading. Double lap connections were assembled and the ultrasonic measurement method was employed to obtain the real-time preload of the bolts. Accelerated corrosion tests of specimens were used to achieve four corrosion levels and the and the corresponding weight loss ratio of the specimens varied from 0 to 10.1%. Fatigue test was then performed on eight corroded connections. The preload change of bolts after installation, corrosion tests, and certain number of load cycles was measured. It is found that the corrosion effects on the bolt preload loss was significant, and an average value of 41.2% preload loss was observed for specimens of 10% weight loss. The influence of fatigue load on the preload loss after unloading could be ignored, but the combination of tensile loading, fatigue loading, and corrosion damage could lead to an up to 11% preload loss.

The Effect of Glue Cohesive Stiffness on the Elastic Performance of Bent Wood-CFRP Beams.

This paper presents experimental, theoretical and numerical studies of wood-CFRP beams bonded with polyurethane (PUR) adhesive. The analyses include two types of CFRP (carbon fibre-reinforced polymer) strengthening configurations and pure glue laminated timber beams as a reference. Through detailed analyses of a double-lap connection on blocks with and without CFRP strips, the authors state that neglecting the cohesive stiffness of adhesive layers may lead to an overestimation of an overall beam’s stiffness. This is significant with wood–CFRP connections, which showed values two times lower than with wood–wood connections. Theoretical modelling of the equivalent area used in a theory of composites provided much stiffer behaviour of the beams than in laboratory experiments. It proves that a PUR glue eliminates the possibility of using simple models that assume a perfect connection between bonded parts. These conclusions led the authors to use the finite element method (FEM) to take into account the cohesive stiffness. The FEM, based on the properties obtained from a double-lap joint analysis, allowed for the precise prediction of the elastic stiffness of the beams.

Static and fatigue behavior of pultruded FRP multi-bolted joints with basalt FRP and hybrid steel-FRP bolts

This study investigates the effect of bolt types on the static and fatigue performance of basalt fiber-reinforced polymer (BFRP) multi-bolted double-lap connections. Three types of bolts are used: stainless-steel (SS), BFRP, and hybrid steel-FRP (HSFRP) bolts. Firstly, static tensile tests using steel single-bolted double-lap connections are conducted to determine the mechanical properties and failure modes of the proposed bolts. Secondly, static and fatigue tests using BFRP double-lap connections with six bolts of either SS, BFRP, or HSFRP were conducted. Finally, post-fatigue static tests were conducted to evaluate the deterioration of the composite joints caused by fatigue loading. Load-displacement curves, failure modes, fatigue life, S-N curves, and stiffness degradation are used to evaluate the effect of the bolt type on the behavior of the BFRP joints. Results indicated that SS bolts can be replaced entirely with BFRP bolts without affecting the static and fatigue performance of the joints. In addition, compared to the brittle failure of both the SS and BFRP bolts, the proposed HSFRP bolts exhibited ductile behavior which could be the key to achieving ductile composite structures. Moreover, the HSFRP bolts dramatically prolonged the fatigue life of the composite joints compared to the joints with SS and BFRP bolts.

Numerical and Experimental Research on Delamination of Glulam Elements

AbstractThe paper presents numerical and experimental research on glulam delamination in a double lap connection with predominant shear stresses. Laboratory tests and wide literature survey enabled to determine timber and glue joint parameters. Cohesive zone theory, generally used for epoxy matrix and fiber reinforced composites, was adopted to modelling glue layer delamination in glulam elements. Numerical models were validated with laboratory tests.

Experimental and numerical study of the parameters controlling the behavior of double-lap connections of steel plates bolted to hybrid FRP strips

Fiber-reinforced polymers (FRP) are increasingly being used in strengthening existing structures. The bonding technique for strengthening steel structures was found to be associated with the brittle failure of the adhesive. In 2012, researchers validated the use of bolted hybrid FRP (HFRP) in strengthening steel beams. The current study aims to investigate a wide spectrum of test parameters to compile a reliable database on the interfacial behavior of bolted HFRP–steel connections. An extensive experimental program was carried out on forty-two double-lap HFRP–steel bolted connections under tensile loading. Test parameters included the number of washers, clamping torque, diameter of hole, and spacing of bolts. Results recommend snug-tight bolts to be installed in standard size holes with the use of two washers per bolt. Experimental measurements are utilized to develop a multi-linear load-slip model that can be integrated in finite-element models to facilitate the analysis of this particular type of connection.

Finite element analysis of composite-to-steel type of joint for marine industry

The usage of composite materials makes easier to form complex shapes with the advantage of reducing the weight of the ship. Moreover, composite material is not subject to corrosion, which is the major issue in a marine environment. This paper investigates the design of the adhesively bonded composite-to-steel joint for marine industry. One part of the joint is double-lap connection of steel plate and carbon fibre-reinforced plastics (CFRP), whereas the other part is a CFRP-skin sandwich panel with Divinycell® foam as the core. In order to simulate the behaviour of composite-to-steel joint, the finite element analysis is conducted. The results suggest that the analysed joint could be used in marine applications.

Fatigue behavior of adhesively connected pultruded GFRP profiles

Fatigue experiments on adhesively connected pultruded profiles were performed in a laboratory environment. The first objective was to determine if fatigue limits exist and if so, how their magnitude is compared to real shear stress amplitudes in GFRP bridge structures subjected to fatigue loads. A further objective was to evaluate measurement methods with respect to a possible detection of damage initiation and progression. For the investigation, a symmetric full-scale double-lap connection geometry was chosen in order to eliminate scale effects and to minimize peeling stresses. The experiments showed a fatigue limit at about 25% of the static failure load at 10 million cycles. This corresponds to an average shear stress amplitude in the connections of 2.0 MPa. This value can remain far above average shear stress amplitudes due to fatigue loading in adhesive connections of GFRP bridges. During the experiments, damage initiation and progression were not detected with the chosen set-up. Failures always occurred in a very brittle manner without warning in the adherents.