Şemsettin Temiz

Application of bi-adhesive in double-strap joints subjected to bending moment

Generally, all failures in adhesively-bonded joints begin at the overlap ends because of the stress concentration occurring at the ends. The approach which reduces stress concentration at the overlap ends increases the load capacity and delays the failure. The lower the stiffness of the adhesive used, the lower the stress concentration, and the lower stress concentration gives rise to higher joint strength. In this work, the results of the application of two adhesives, one stiff and one flexible, with very different mechanical behaviors along the overlap length in double strap joints subjected to bending moment, were analyzed. A stiff adhesive was applied in the middle portion of overlap, while a flexible adhesive was applied towards the edges. The results show that the bi-adhesively-bonded joints carry more loads and have higher strength when compared with single-adhesively-bonded joints.

The effect of adherend thickness on the failure of adhesively-bonded single-lap joints

This paper presents an approach to predicting the failure and strength of joints bonded with a film-type adhesive (FM 73) using non-linear finite element method. First, lap-shear tests on Single-Lap Joints (SLJs) with different adherend thicknesses and overlap lengths were carried out and fracture surfaces of the SLJs were examined by scanning electron microscopy (SEM). Then, the stress analyses in the SLJs using a non-linear finite element method were performed by considering both the geometrical non-linearity and non-linear material behaviors of both adhesive and adherend (AA2024-T3), and Finite Element Analysis (FEA) results were compared with experimental results. Two different failure loci were seen when the failure surfaces of the SLJs were examined and both the stress analyses and experimental results showed that a catastrophic failure occured around the central zone of the overlap due to the effect of shear stresses, while the failure at the free edges of the adhesive layer originated from the peel stress in tension.

The effects of overlap length and adherend thickness on the strength of adhesively bonded joints subjected to bending moment

In this work, elasto-plastic stress analysis of a Single Lap Joint (SLJ) subjected to bending moment was investigated using 2D non-linear Finite Element Analysis (FEA). The SLJs, consisting of hardened steel as the adherend bonded by two adhesives, one stiff and one flexible, with very different mechanical behaviors were analyzed. In order to determine the effect of geometrical parameters on the performance of the SLJs, four different adherend thicknesses and overlap lengths for each adhesive were used. For verification of the analysis, the FEA results were compared with experimental results. It was observed that there was a significant effect of adherend thickness on the strength of the joint with both adhesives. However, the load carried by the SLJ with the flexible adhesive increased with increasing overlap length.

Non-linear stress and failure analyses of adhesively-bonded joints subjected to a bending moment

In this paper, the mechanical behavior of the Single-Lap Joints (SLJs) bonded with two different adhesives (FM 73 and SBT 9244) under a bending moment was analyzed, both experimentally and numerically. Four-point bending experiments for the joints with different overlap lengths were carried out and fracture surfaces of the SLJs were examined with a Scanning Electron Microscope (SEM). After the stress analysis in the SLJs was performed via a finite element method by considering the material non-linearities of the adhesives and adherend (AA2024-T3), the Finite Element Analysis (FEA) results were compared with experimental results. Finally, the stress analyses and experimental results show that the failure in the SLJs subjected to a bending moment probably initiates from the overlap region on the adhesive–upper adherend interface in tension and propagates towards the centre of the overlap. Also, in the joint subjected to a bending moment, it is seen that the load carried by the SLJ with SBT 9244 adhesive with increasing overlap length is more than that of the SLJ with FM 73 adhesive, although in the bulk form FM 73 adhesive is about three times stronger than SBT 9244 adhesive.

Effect of Curing Pressure on the Strength of Adhesively Bonded Joints

It is important to be able to predict the mechanical response of adhesively bonded joints. To succeed in this, the accurate simulation of the behavior of adhesively bonded joints is an essential requirement because of the strain rate, temperature, and hydrostatic sensitivity of adhesive properties, which should be taken into consideration when developing a material model [1-11]. On the other hand, the load capabilities of adhesively bonded joints are affected by both applied pressure and temperature during cure. For this reason, in this study, the tensile load capabilities of single lap joints (SLJs) bonded with a flexible adhesive that possesses pressure-sensitive properties were experimentally investigated with respect to the applied pressure during the curing operation, and the experimental results were compared with finite element analysis (FEA) results. Finally, in addition to other parameters, such as the dependence on strain rate and the lack of yield criteria of adhesives, it was seen that the residual thermal stresses that occurred as a result of the applied pressure during the curing process at elevated temperature need to be taken into consideration to accurately simulate the mechanical behavior of adhesively bonded joints.

Effect of overlap length on durability of joints bonded with a pressure-sensitive adhesive

In this study, the effect of overlap length on durability of a film type adhesive, Structural Bonding Tape (SBT) 9244, which possesses pressure-sensitive and visco-elastic properties, was investigated. Single-lap joints with 1.62 and 3.2 mm adherend thicknesses and at 12.5, 25 and 50 mm overlap lengths consisting of AA2024-T3 alloy as the adherend were exposed to two environmental conditions for exposure times of up to 90 days. The exposure environments were 100% relative humidity (RH) and 3.5% NaCl solution. At the end of exposure times, the failure surfaces were examined by Scanning Electron Microscopy (SEM) after the strength of joints was determined with the lap shear test. It was observed that with increasing overlap length, not only the failure load increased, but also the degradation rate decreased. In addition, as the metal adherends do not absorb any water and moisture from the environments, the metal adherend thickness had no effect on durability of the adhesively bonded joints.

FE Stress Analysis of Thick Composite Laminates with a Hole in Bending

In this work, the stress analysis of isotropic and ortotropic laminae both with a hole and without a hole and laminated both with a hole and without a hole composite plates have been examined using the finite element method. In order to solve the problem, a computer program has been written by using characteristics of eight-node isoparametric plane element. The calculations have been tested on various composite and steel materials by this program. The results have been shown in diagrams and tables and compared with literature. It was observed that the stress distributions in the plate with a hole was totally different from the plate without a hole. The analyses have showed that, the elastic stresses have been gradually reduced as moving from the first layer to the second.

Determination of Mechanical Properties of Double-Strap Adhesive Joints with an Embedded Patch

In this study, stress analysis of double-strap joints used to fasten parts, particularly in aircraft and automotive industries and in the repair of damaged parts, was done using the finite element method. In classical double-strap adhesive joints, patch parts are bonded to the outer surface and these parts resist air flow. To decrease this effect and for constructive and aesthetic requirements, patch parts were embedded into the adherends. The effects of embedded patch parts on failure loads and stress distributions were investigated experimentally and numerically. For this purpose, AA 2024-T3 aluminum adherends with four different thicknesses (4.8, 5.6, 6.4 and 7.2 mm) were bonded as double patches with 0.4, 0.8 and 1.2 mm spring steel patch thicknesses and 20, 40 and 60 mm overlap lengths. The stress analyses were done under plain strain assumption. To verify the finite element model, experiments were carried out. The results show that adherends and patch thicknesses as well as overlap length all have considerable influence on failure loads and stress distributions.

ÇEKMEYE MARUZ ARA BOŞLUKLU ÇİFT TAKVİYELİ YAPIŞTIRMA BAĞLANTILARINDA GERİLME ANALİZİ

Havacilik ve uzay sanayisinde, otomotiv sektorunde meydana gelen kazalar, ozellikle ucaklarin kalkisi ve inisi esnasinda pistte bulunan kum tanecikleri ve partikullerin ucak govde ve kanatlarina yuksek hizla carpmasi sonucunda asinma, yirtilma, catlak gibi hasarlara sebebiyet vermektedir. Bu yirtilmis, catlamis veya zayiflamis olan hasarli bolgenin hassas bir sekilde onarilmasi gerekmektedir. Yirtik ve catlak ilerlemesinin durdurulmasi veya zayif olan bolgenin onarilmasi icin hasarli olan bolgenin kesilip cikartilmasi ve kesilen bolgeye yama yapilmasi gerekmektedir. Hasara ugramis bolgeler genellikle kucuk capli bolgeler olup onarilmasinda komple bir parcayi yenilemek yerine hasarli olan bolgede islem yapmak, ozellikle iscilik, maliyet ve zaman gibi kavramlarin cok onemli oldugu gunumuz icin uygun olacaktir. Hasarli olan bolge kesilip cikartilip cift tarafli yama kullanildiginda yamalar arasinda bosluk olusmaktadir. Bu calismada ayni bindirme uzunlugunda kapaklarla farkli boylarda ara bosluklar olusturulmus, kapak kalinliginin, bindirme uzunlugunun, parca kalinliginin ve ara bosluk boyunun cekmeye maruz yapistirma baglantilarin mukavemeti uzerindeki etkileri incelenmistir. Bu amacla, 4.35, 5 ve 6 mm kalinligindaki AA 2024-T3 aluminyum levhalar, 40, 50 ve 60 mm bindirme uzunluklarinda, 0.6, 0.8 ve 1 mm kalinliklarinda yuksek karbonlu celikten imal edilmis kapaklarla ve 10, 15 ve 20 mm ara bosluklu yapistirilarak baglanti numunesi elde edilmistir. Yapistirici malzemesi olarak CYTEC FM®73 yapisal film yapistirici kullanilmistir.

A study on durability of joints bonded with pressure-sensitive adhesives

The use of adhesive bonding as fastener presents very high usage potential, especially for different environments. However, the designers do not have enough data yet to address the changes in the mechanical properties of adhesives in the course of time. In this study, the ageing of film-type adhesives, Structural Bonding Tapes (SBT) 9244 and 9245, which are different in thickness and possess pressure-sensitive and visco-elastic properties, was investigated. First, the bulk adhesive specimens were prepared and exposed to two different environmental conditions until saturated. In the same time, single lap joints with two different adhesive layer thicknesses, consisting of AA2024-T3 as the adherend, were exposed to the same environmental conditions for exposure times of 90 days. The immersion environments were 100% relative humidity (RH) and 3.5% NaCl solution. At the end of exposure time, the failure surfaces were examined by Scanning Electron Microscopy (SEM) after the strength of joints was determined with the lap shear test. Both SBT adhesives absorb more water from 100% RH than from 3.5% NaCl solution and, therefore, they deteriorate rapidly in 100% RH. In addition, as the thickness of adhesive layer increases, the loss in the strength increased.