Asymmetric Double Cantilever Beam Specimens Research Articles

An investigation on effects of acid etching duration on adhesive bonding of polyethylene to E-glass/epoxy composites

The quality of bonding between the liner and composite shell of a type IV pressure vessel is a crucial point to prevent the leakage of this vessel subjected to fill and refill cycles. In the present research, acid etching was used for surface treatment of a plastic liner to increase the bonding strength. The numerical and experimental study was conducted to investigate the effect of surface treatment duration on the adhesive bonding of E-glass/epoxy composites to the polyethylene (PE) liner. The contact angle and asymmetric double cantilever beam (ADCB) tests were performed to determine the bonding strength. According to results, by increasing acid etching exposure time, bonding strength increased and adhesive bonding became more stable. It was also found that 120 min acid etching exposure time of PE presented the lowest contact angle on the surface of PE; and the highest strain energy release rate (SERR) in ADCB specimens. The virtual crack closure technique was used to simulate the delamination initiation of ADCB specimens in Abaqus 6.14. The numerical results of Gc for the crack initiation deduced by the virtual crack closure technique were consistent with the experimental data. It was observed that the magnitude of GII/Gc was larger than that of GI/Gc. Also, nailing phenomenon was observed in the crack tip of ADCB specimens and was remarked as two jumps in the distribution of mode II SERR across the width of ADCB specimens.

Effects of aluminum surface treatments on the interfacial fracture toughness of carbon-fiber aluminum laminates

The influence of aluminum surface treatment on the interfacial delamination performance of carbon/epoxy composite and aluminum substrate was studied. Aluminum substrates were treated chemically with acid, alkaline and both individually. AFM images suggest high roughness for acid treatment and porous oxide layer for alkaline treatment, respectively. The plate theory was employed in order to obtain the energy release rate of asymmetric double cantilever beam (ADCB). The results indicated improvements of interfacial fracture toughness for acid then alkaline treatment of aluminum substrates. Finite element study of crack growth proved more reliability of energy release rates obtained by plate theory analysis rather than compliance calibration method, for ADCB specimen.

Comparison of numerical, empirical and local partition methods in ADCB specimens

It is well-known from the scientific literature that the asymmetric double cantilever beam (ADCB) specimen is subjected to mixed-mode I/II load at the crack tip. In these samples, the crack plane lies outside the laminate midplane. In this work, the energy release rate in modes I and II (GI and GII) are obtained by different approaches. The analytical determination of GI and GII in ADCB samples is not simple or straightforward and is usually based on partition methods. Numerical results obtained from finite element analysis (FE) are compared with the analytical local partition method (LP) for a carbon fibre epoxy AS4/3501-6 laminate. Both results are also compared with an empirical formulation obtained in previous works. Results obtained from all three methods are in good agreement.

Elastic–plastic analysis of Asymmetric Double Cantilever Beam specimen

The present paper studies theoretically non-linear fracture behavior of Asymmetric Double Cantilever Beam (ADCB) specimen made of unidirectional fiber reinforced polymer composite. The crack arms of ADCB have different heights. Loading configuration consists of two bending moments of the same senses and equal magnitudes applied to the crack arms. The composite material building the beam is assumed to obey stress–strain relation of an elastic-perfectly plastic material. Investigation is performed by means of path independent J-integral. Closed form analytical solutions of J-integral are obtained for every typical level of stresses and strains in the cracked as well as un-cracked beam portion. The influence of crack position on J-integral is also analyzed. A numerical example is presented to show the influence of material non-linearity on J-integral. It is found that the J-integral value increases when material non-linearity is taken into account. This is attributed to the strain energy dissipation due to plastic deformation of the beam.

Influence of the principal tensile stresses on delamination fracture mechanisms and their associated morphology for different loading modes in carbon/epoxy composites

In this study, the delamination toughness under pure modes I and II and a 2/1 mode mixity ratio and the associated fractures morphology of AS4/8552 and AS4/3506-1 unidirectional carbon fibre/epoxy composites have been related to the principal tensile stresses at the crack front.Pure modes I and II and a GI/GII=2/1 mixed-mode ratio tests were respectively carried out by means of the following methods: DCB (Double Cantilever Beam), ENF (End Notch Flexure) and ADCB (Asymmetric Double Cantilever Beam). ADCB specimens, in which the crack plane is outside the laminate midplane, are simple as well as useful test configurations to produce a mixed-mode load state at the crack tip of samples. As the ADCB test is not still covered by international standards, the calculations were performed by means of FE models and analytical formulations developed in previous studies.The Finite Element Modelling (FEM) method was used to analyze the stress state ahead of the crack to better explain the fracture micromechanisms acting under different loading modes and their influence on delamination fracture toughness.It has been demonstrated that the direction of the principal tensile stresses at the crack front has a major influence on the orientation of the so-formed microcracks, on microcrack coalescence and, hence, on the failure mode description reflected in the fracture morphology.

Influence of the Mode Mixity Ratio and Test Procedures on the Total Energy Release Rate in Carbon-Epoxy Laminates

In this work, the fracture behaviour under modes I, II and different mixed mode I/II ratios has been studied for a AS4/3501-6 carbon fibre epoxy resin laminate. Mixed Mode tests were carried out by means of two different procedures: MMB (Mixed Mode Bending) and ADCB (Asymmetric Double Cantilever Beam). ADCB specimens, in which the crack plane is out of the laminate midplane, are simple and useful test configurations to produce a mixed mode load state at the crack tip of the samples. The ADCB test is not still covered by international standards, so the calculations were performed by means of the Finite Element Modelling (FEM) and analytical formulation developed in previous works. FEM was used in order to analyze modes I, II and mixed I/II and to compare the experimental and numerical results. It was found a good agreement between ADCB and MMB tests. On the other hand, it was also observed that the critical energy Gc increased as the mode mixity ratio GII/Gc increased. Finally, experimental and numerical results showed a good agreement as the differences obtained from both procedures were generally lower than 10%.

ＤＣＢ試験片を用いた塗装鋼板の塗膜／鋼板界面の破壊じん性評価

A method for evaluating the interfacial adhesion strength between paint layer and chromate-coated steel sheet in the paint-coated steel sheet system was proposed. Three kinds of the steel sheets modified with chromic acid which contained various content of colloidal silica and a paint composed of a mixture of alkyd resin and silica particles were used as specimens for the experiment. The adhesion strength was evaluated by the critical strain energy release rate at interfacial crack initiation. To measure the critical strain energy release rate, an asymmetric double cantilever beam specimen was used, where an interfacial pre-crack was induced between the paint layer and steel sheet. When the crack propagates along the interface between paint layer and chromate-coated steel sheet, it was observed that the critical strain release rate increase with increasing the content of colloidal silica in the chromate-coated steel sheet. Similar dependency of the silica content on the adhesion strength had been also confirmed in the cross cut tests. This signified that the interfacial adhesion strength could be evaluated quantitatively by the critical energy release rate.

Effect of Mode-mixity on the Fracture Toughness of Ti-6al-4v/fm-5 Adhesive Joints

Using several different fracture tests, the fracture toughness of a chromic acid anodized titanium (Ti-6A-4V)/polyimide (FM-5) adhesive system was evaluated. Mode I, mode II, and mixed mode (I and II) tests were conducted using double cantilever beam (DCB), end notch flexure (ENF), and mixed mode flexure (MMF) geometries. Interfacial type failures were observed in the ENF and MMF specimens as a result of the mode II loading inherent in these tests. Pure mode I loading, as is the case with symmetric DCB specimens, resulted in cohesive failures with a fracture energy around 2500 J/m2 on as-received specimens. The asymmetric DCB specimens had fracture energy values around 2000 J/m2, the MMF specimens close to 1970 J/m2, and ENF specimens around 1300 J/m2. All the above measurements were made on as-bonded (unaged) specimens. Titanium/FM-5 bonds supplied by the Boeing Company were then aged in one of three different environments for 2 and 6 months respectively. The environments included: 177degC in air and 2 psia, and 204degC in air. Following the aging, DCB, ENF, and MMF tests were conducted on the specimens. The results showed that aging in all three environments resulted in decreases in fracture energy for the above specimen testing configurations. The largest drop (20 percent) in fracture toughness was noted in specimens aged for 6 months in air at 204degC. An unusual finding from this study, in contrast to what other researchers have seen on other systems, was that increasing mode II loading resulted in significant reductions in toughness. Crack path selection and interaction with the woven glass scrim within the bonded specimens may be responsible for the lower mode II fracture energies. From the tests conducted, failure envelopes were developed to predict failure energy and type for use in designing structural joints.

Tailored adhesion at polymer/nonpolymer interfaces

AbstractIn this investigation, block copolymers of deuterated polystyrene (dPS) and poly (2‐vinylpyridine) (PVP) have been used to modify the adhesion at polystyrene/soda lime glass interfaces. The fracture energy, Gs of these interfaces was measured using an asymmetric double cantilever beam specimen. The failure mechanism was investigated using forward recoil spectrometry (FRES) and Rutherford backscattering spectrometry (RBS). The areal density, ∑ of the dPS‐PVP block copolymer at the two fracture surfaces, as well as the fraction of the dPS block on the PS side of the fractured sample are measured directly by FRES. The fraction of the PVP block on the glass side of the interface can be found by quaternizing the PVP with methyl iodide and then using RBS to measure the amount of iodine on each fracture surface. Short dPS blocks (NdPS < 175) do not entangle effectively with the PS homopolymer and only very small increases in Gc can be achieved as the dPS block pulls out of the interface. If the dPS block is long (NdPS ≫ 175) and if ∑ is large, crazes can develop in the PS ahead of the crack. The crazed interface fails at low ∑ by breaking the block copolymer close to the styrene/vinylpyridine link. At higher ∑, if the PVP block is relatively short (NPVP = 95), the crazed interface fails by the PVP block being pulled off the glass. If both the PVP and dPS blocks are long (≫ 175), the Gc increases rapidly with increases in ∑, but the interface becomes so strong that the glass on the thinner side of the test specimen breaks. The dPS block and the PVP block are found on opposite sides of the fracture surface with most of the PVP on the glass and most of the dPS on the PS side of the interfaces. Finally, if the glass surface is modified by coating it with a self‐assembled hydrophobic monolayer produced from chlorodimethyloctadecylsilane (CDMOS), the interface becomes very weak and fails by pull‐off of the PVP from the CDMOS‐coated glass. Using these results it is possible to tailor the interfacial adhesion to produce a desired Gc within a wide range of possible values. © 1994 John Wiley & Sons, Inc.

Analysis of a mixed mode fracture specimen: the asymmetric double cantilever beam

An asymmetric double cantilever beam (ADCB) is a simple but effective specimen for the measurement of polymer/polymer and polymer/non-polymer bimaterial interface fracture toughness. In order to characterize fully the bimaterial interface strength, and to control the crack trajectory, the critical energy release rate, Gc, and the phase angle, ψ, of the applied stress field as functions of loading and geometry of the specimen should be obtained. For most practical cases, ψ has to be evaluated numerically. In this work, a boundary element analysis is carried out to obtain G and ψ for the ADCB specimen at different material and geometry combinations. An expression for the energy release rate, G, based on Kanninen's beam on elastic foundation model is compared with the numerical results. Limitations on the use of the ADCB specimen are also discussed.