Theses supervised by Prof. Dr. Ramazan Karakuzu
20 theses · Dokuz Eylül University
Impact characteristics of laminated composites
In this study, the influence of size and location of embedded delamination on impact behavior of laminated composite is investigated, experimentally. The fiber-reinforced composite materials used in this study was manufactured at Composite Laboratory in Dokuz Eylül University, and was prepared by cutting defined size for tests in Izoreel Firm, and they consist of 12 plies lamine is designed as defined orientation.The specimens were produced as for with and without delamination by vacuum assisted resin infusion molding method (VARIM). As matrix materials, the mixture of Durateks DT E 1000 epoxy and Durateks DT S 1105 hardener resin; and as reinforcement materials, unidirectional E-glass fabric were used. The experiments were performed by using Ceast-Fractovis Plus impact test machine. As a result of the experiments, the location of delamination on the impact behavior is seen to be more effective than the size of delamination.
Core material effect on impact behavior of glass fiber sandwich composites
The objective of this thesis is to investigate the effects of core material and its thickness on impact behavior of sandwich composite plates subjected to low velocity impact, experimentally. Two PVC foams and PET foam were selected as the core material, having approximate density of 60 kg/m3 and thicknesses of 5, 10 and 15 mm. The stacking sequence of the sandwich composites are [+45/-45/0/90/core/90/0/-45/+45].Impact tests were carried out by using Fractovis Plus Impact testing machine under room temperature. Various impact energies were selected from 10J to 70J to analyze the impact energy level. The dimensions of the specimens are 100 mm x 100 mm. After the impact tests, absorbed energy, maximum contact time, maximum deflection and maximum contact force versus impact energy, contact force versus deflection and contact force versus time curves were obtained for mentioned impact energies for sandwich composites with PVC and PET foams, and [+45/-45/0/90] laminated composites.As a result, it is seen that the core material and its thickness have notable effects on the impact behavior of sandwich composite plates. Sandwich composites have also higher absorbed energy, penetration and perforation threshold.Keywords: Sandwich composite, PVC foam, PET foam, Core thickness, Low velocity impact
Ballistic performance of hybrid composite structures
The aim of this study is to numerically investigate the ballistic behavior of composites with different thicknesses and different reinforcements. The guns were shot at four different velocities on composite models using armor-piercing 7.62 M61 AP projectiles. The alumina ceramics forming the front surface of the composite structure were used in three different thicknesses, 6 mm, 8 mm, 10 mm. The fabric-reinforced epoxy composite, which forms the back surface of the composite structure, is modeled to have six different compositions in total, using three different reinforcing elements, with a total thickness of 10 mm. Aramid, S2 glass and hybrid carbon-aramid fabrics were used as reinforcement. In addition, the aramid/S2 glass/epoxy model has been produced at three different thickness ratios, with aramid and S2 glass fibers having a total thickness of 10mm. In the study, Ansys was used as preprocessor and Ls-Dyna as solver. Multilayer MAT 59 and MAT 22 for composite materials; MAT 110 material cards were used for alumina ceramic material. For the composite structure: 72 different numerical analyzes were performed for four different velocities, three different ceramic thicknesses and six different composite compositions. As a result, the numerical analysis revealed that the alumina/S2 glass/ epoxy composites had a higher ballistic performance than the others in the data, based on the input-output velocity of the projectiles when the areal density of armors is not considered. Also, when the all ceramic thicknesses and areal density of armors are considered, it is found that the aramid/epoxy backing plate had a higher ballistic performance than the others.
Darbeli yüklemeye maruz kompozit borularda deniz suyunun etkisi
The aim of this experimental study was to investigate the sea water effect on fatigue behavior of composite pipes subjected to impact loads.In this study, firstly, the general data about burst strength (load capacity) and average life cycle of fatigue composite pipes are given. Manufacturing of vessels by filament winding method is expressed. Schematic of a filament-winding process is demonstrated and also materials of filament winding and applications of filament wound products are given. Information and procedure about impact and fatigue tests are given.Secondly, impact tests and fatigue test results are presented. The impact tests are performed at three different energy levels as 5J, 7.5J, and 10J at room temperature. The impact characteristics such as peak force, maximum deflection and total absorbed energy are listed. The mentioned impact characteristics of both conditions (dry condition and sea water immersion) are plotted against the impact energies. Using of load-deflection and load-time curves the impact properties of filament wound-glass fiber reinforced plastic (FW-GFRP) pipes are discussed for both conditions. Fatigue life cycles of FW-GFRP pipes and graphs of cycle to failure for all test specimens are given. Damage mechanisms (modes) of composite pipes are examined in detail.The results obtained are evaluated and discussed by using some graphics and images. Remarkable finding is observed that impact and burst strength values of composite pipes which are exposed sea water (three months) are increased a bit.
Investigation of sea water effect on impact behavior of laminated composite plates
The aim of this study is to investigate the sea water effect on impact behavior of glass-epoxy laminated composite plates. Therefore, 135 pieces of specimens were prepared in dimensions of 100 x 100 mm with thickness of 3 mm. Impact tests of specimens were conducted by the Fractovis Plus Impact Test MachineThe experimental phase of this study consists of five stages. In each stage 27 specimens were used. In first stage, dry specimens were used and in last four stages, wet specimens were used. In these specimens, seawater immersion times were chosen as 1, 3, 6, 9 months. Before the impact test, the masses of dry and seawater immersed specimens were measured by sensitive weighing machine to calculate the amount of water absorption. Specimens were impacted at impact energies, 10J, 20J and 30 J and impactor masses, 5 kg, 10 kg and 15 kg.The absorbed energy, maximum contact force, maximum deflection and maximum contact time were obtained according to the seawater immersion time. From the obtained results, it?s observed that the specimen that has longer immersion time, the absorbed energy of the specimen has decreased but the contact time has increased.
Seawater effect on behaviors of impact and axial compression-after impact of composite pipes
The aim of this thesis study is to investigate the effect of the seawater on impact behavior and axial compression after impact strength of the composite pipes having four different diameters and approximately 1.75 mm wall thickness. E-Glass/epoxy pipes with [±55o]3 orientation were fabricated using filament winding process.Specimens, dry and immersed in seawater for 3-, 6-, 9-, and 12-month, were subjected to transverse impact having 15J, 20J, and 25J energies, using instrumented Fractovis Plus impact testing machine at the room temperature. Following, variation of contact force versus time, contact force versus deflection, contact force versus seawater immersion time, absorbed energy versus seawater immersion time, maximum deflection versus seawater immersion time, and contact time versus seawater immersion time for above impact energies are driven.Also, the axial compression after impact tests was carried out by using Universal Shimazdu AG-X testing machine and the compressive strength versus seawater immersion time diagrams is driven. Results show that the seawater has significant effects on transverse impact behavior and the compressive strength of the composite pipes.
Impact loading in laminated composites
The aim of this study is to examine the damage and deformation (prediction, initiation and propagation), to criticize -when and which conditions they can occur- with experimental results and to compare them with finite elements results, and then comment on them. The specimens that used during the experiments are produced in Izoreel Company, and they examined with Fractovis Plus impact tester machine in different initial impact energy levels, initial velocities, and initial impactor mass. The matrix material of the specimen is made of with the mixture of CY225 epoxy with HY225 hardener resin. And the unidirectional e-glass fabric having weight of 509 g/m2 is used as reinforcing material. Specimen geometry is square with 100 mm of per edge. The sequence is in [0/30/60/90]s form. A ForTran-based 3D impact finite element code had chosen to solve both [0/30/60/90]s and other fiber orientations.The specimens tested in ternate groups. It is aimed here to examine the effects of velocity, mass and impact energy. The threshold value of the contact force that delaminations occur is examined, and also it is examined if this value could be predicted with the finite element code or not. The delamination areas and the delamination ratios are computed with a pixel-based image processing code precisely. At last, the composite laminates -that had not been experimented like the twice and third as the laminate thickness- have solved with 3D impact code, and the results have discussed.The last addition to the impact experiments is about the fiber orientations. The non-experimented specimens as [0/l5/-15/90]s, [0/30/-30/90]s, [0/60/-60/90]s, [0/75/-75/90]s had solved with finite element code, too.
Environmental effects on pin-loaded laminated composites
The aim of this study was to study the effect of the sea water on the bearing strength behavior of the glass-epoxy laminated composite. The ratio of the edge distance to the pin diameter, and the ratio of the specimen width to the pin diameter (W/D) were systematically varied during experiments. The ratio of the edge distance to the pin diameter were changed from one to five and the ratio of the specimen width to the pin diameter were selected as three and four for this study. The hole of the plate is subjected to a traction force by a pin.For this study, layered composite materials were manufactured, at İzoreel firm, at one hundred and twenty degree Celsius and under two hundred and fifty kilo Pascal pressure. Two different stacking sequences were choosen. One of them was produced at zero degrees orientation angle of fiber to obtain the mechanical properties of the laminated composite material. The mechanical properties of the laminated composite material were obtained from standard tests by absorping natural water and sea water. Second one was of stacking sequence zero degrees and ninety degrees multiply three with the symmetric of them to investigate the effects of sea water on the bearing strength behavior of the laminated composite.Failure modes and maximum failure loads of the specimens are found in experimental study. Experimental study includes one, three, six and nine month periods for absorption of sea water into glass fiber-epoxy composites. So the specimens kept into sea water one, three, six, and nine month periods. For every period, failure modes and maximum failure loads of the specimens are found in experimental study.
Impact on laminated composites
An impact is a force which is applied over a short time period. Such a force can sometimes have greater effect than a lower force applied over a proportionally longer time period. Although many structures are some time subjected to these kinds of forces, many machines and machine parts are commonly subjected to such forces. That is why impact on materials has a big importance in mechanics. Impact on metallic materials will not result in greater effects because metallic materials have the ability to plastic strain and this will help them to absorb most of the energy which will occur as a result of the impact. On the other hand, the deformation which will occur as result of an impact on a composite can occur in an unexpected way and on an unexpected surface.In this thesis it is discussed, the damage and the deformation of composites under different impact energies. Also it is discussed, in which conditions they can occur, by the help of experimental results and the experimental results are compared with finite element results.The specimens that are used during the experiments are three kind of geometrical shapes; square with 76 mm per edge, square with 150 mm per edge and a circle with 76 mm of diameter. They are examined in Fractovis Plus impact tester machine.
Effect of hole number to bearing strength in pin loaded composite plates
The aim of this study is to research failure mode, failure load and bearing strength in alaminated glass-vinylester composite plate with two parallel circular holes, which aresubjected to traction forces by two parallel rigid pins. The behaviour of pin loadedcomposite plates has been observed experimentally and numerically with differentdimensions.These are performed at three different modes; the distance from the free edge of theplate to diameter of holes (E/D) ratio (1,2,3,4,5), the distance between upper part of plateand centre of holes to diameter of holes K/D ratio (2,3,4) and the distance between twoholes to diameter of holes M/D ratio (2,3,4,5). The failure analysis is performednumerically and experimentally and the orientation of fiber ? =0° is constant during study.Failure types and failure loads on the specimens have been determined fromexperimental study. In numerical study, three dimensional finite element method was usedby assistance of LUSAS 13.6 finite element analysis program. In this program, maximumfailure load is found with nonlinear analysis. Hashin failure criteria is used in this failureanalysis. In the case of failure, appropriate properties of the nodes failed of the compositeplate are reduced.The experimental results are compared with the numerical results and it has been seenthat a good agreement between experimental and numerical results.
Damage in laminated composite plates subjected to low-velocity impact
The aim of the study is to investigate the impact response of laminated composites were constructed from orthotropic layers containing collimated unidirectional fibers or woven fabrics made of glass fabrics and an epoxy matrix. The effects of the following parameters on the impact resistance of composite plates were studied: the angle between adjacent layers, weaving gaps, the curing pressure, the size of weaving cell, the stitching reinforcement through the composite thickness and the weaving angle between fill and warp yarns.An instrumented drop-weight impact testing machine was used in the investigations. Because of the special fiber geometries involved in the study, all woven composites were fabricated manually. Some of the composite prepregs were stitched after stacking together by hand, using a needle. The perforation threshold, peak force and bending stiffnesses were identified to be the primary impact characteristics of the composites.Experimental results reveal that weaving with gap and curing with low pressure increases the perforation threshold. The perforation thresholds increases as the angles between adjacent layer and the weaving angle between fill and warp yarns decrease. Since the fill and warp yarns constrain the damage propagation, the cell size plays an important role in the damage process. Damage size and perforation threshold reduce with stitching.A numerical evaluation was carried out by using a finite element code. The contact force history between impactor and the composite plate consist of unidirectional plies was found for the specimens which occurred no fiber breakage in experiments. The experimental results and numerical results are reasonable.
Failure strength of laminated composite plates with multi-pin loaded holes
The aim of this investigation is to study the failure behavior and the effect of different geometries of glass-epoxy laminated composite plate which is subjected to a traction force by 4 rigid pins. The behavior of multi-pin loaded composite plates which have the stacking sequence of (0 / 90 / plus-minus 45)s and approx. 60 percent fiber volume fraction has been observed experimentally and numerically. The quantity of the different geometries investigated in this study were 72 which consist of 2 geometric series (Series A, Series B) and 3 different hole distance parameters (The ratio of `edge distance? to `hole / pin diameter? E/D:2,3,4 ; The ratio of `Longitudinal hole distance? to `hole / pin diameter? F/D:2.4.6 ; The ratio of `Transverse hole distance? to `hole / pin diameter? G/D:2,4,6,8) The three-dimensional finite element method was used to obtain stress distribution of the material. For analyzes, LUSAS 13.6 finite element analyze software has been chosen. During the study geometric non-linear analyze method and ?Hashin Failure Criteria? have been selected to determine the ?Failure Mode? and the ?Failure Load?. The results of numerical and experimental study have been plotted and compared with each other.
Kompozit yapılar için bağlantı çözümleri
Lightweight composite materials are continuously improving and have applications in almost every technology field, from rocket science to everyday household appliances. There are many opportunities from the design, performance, operability, and reliability standpoints. Besides these opportunities, challenging topics are open for improvement, especially in securely joining composite parts. Conventional fastening systems like rivets, welding bolts, and clinched fixings were commonly designed for sheet metals or thick construction parts, which may often be incompatible with composites or require additional work when applied to the composite materials. On the other hand, embedding fasteners into composite materials requires molding to adapt to the fastener geometry, which can provide a seamless connection between the assembly components. However, embedding unfamiliar parts may lead to design compatibility issues and inefficient processes in real-life scenarios. In this thesis, a method was researched and analyzed to improve the load-carrying capacity of single-lap composite structures using a sleeve geometry designed to be formed by a special bolt in the assembly field. The proposed model reduced the failure indices by 16% to 54%, reducing the clamp loss ratio by 18%, and improved the damage initiation force by 8% to 40% compared to similar alternatives. The bearing response and the bearing stiffness were significantly increased with this thesis.
Dinamik yükler altında bağlantı elemanlarının davranışlarının incelenmesi
This work aims to improve the understanding of bolt behaviors in dynamic load scenarios, particularly those influenced by transverse loads. In order to forecast fastener outcomes under varying load situations, a comprehensive investigation was conducted encompassing experimental, theoretical, machine learning, and simulation-based study methodologies. Findings indicates that bolts subjected to vibratory loosening are more susceptible to experiencing increased friction in their bearing and thread sections. This is primarily caused by wear in the contacting regions resulting from both macro and micro slips. Therefore, the capacity to reuse fasteners becomes uncertain in certain situations. Experimental results have shown that the type of coating used also has a significant effect on the behaviors observed. A simulation model was developed to address the challenges of conducting repeated experimental testing, specifically focusing on the factors of tightening, friction change, and loosening. The simulation approach enables researchers to predict the effects of fastener loosening risks. The solve time for the loosening simulation might be significantly increased depending on the thread mesh density. A neural network-based deep learning technique and model were created to address this problem. Model was trained using both experimental data and simulated outcomes. To manage the function errors, the Mean Squared Error (MSE), Mean Squared Deviation (MSA), and R-squared values are used. The model loop built in this context is designed to optimize the parameters during the training process and identify the most favorable scenarios. This enables us to input experimental and simulation data into the neural network in the future, hence enhancing the program's dependability without making any modifications to the underlying code. The last part of the study primarily examines the theoretical foundation of bolt stresses and the lifespan of loosening effected bolts. Calculations were conducted using cantilever beam theories, which is a widely used method for analyzing load instances in bolted joints. A methodology has been built to forecast the fatigue life of the bolt based on its transversal fatigue life when subjected to repetitive tightening. This methodology utilizes cumulative damage theories. Results obtained from the experimental investigation and theoretical assumptions fall within an acceptable margin of error. This theory allowed for the transformation of transversal displacement inputs into lateral shear and force values. These values were then used to make predictions about the lifespan of structures under loosening conditions. This approach also incorporates the computation of bearing friction affects and load transfer capabilities. An increase in the shear load capacity results in an increase in the bending moment while maintaining the same transverse displacement. This increase in bending moment leads to a decrease in the fatigue life of the bolt. This is also consistent with the findings of the friction change test conducted during repeated tightening Junker vibration testing, where samples fail due to bending fatigue. It is crucial to consider the reusability of the fastener when analyzing high transverse loads so as to improve the precision of its estimated lifespan.
Solenoid dizel enjektörlerde valf yuvası yüzeyine uygulanacak ön şekillendirme işlemi ile parçacık erozyonundan kaynaklanan hasarlı yüzeylerin iyileştirilmesi
Ortak hat sistemi, modern dizel motorlarda en çok kullanılan enjeksiyon teknolojisidir. Bu sistemin en önemli parçalarından biri silindir içine 2500 bar'a kadar basınçta yakıt püskürten enjektörlerdir. Bu yakıt sisteminde en çok kullanılan enjektör tipi, elektro valf ile kontrol edilen selenoid valfli dizel enjektörlerdir. Valfin kontrol hacmi etrafındaki kuvvetlerin dengesi, selenoid valfin kontrolünü sağlar. Yakıt, Elektronik Kontrol Ünitesi (EKÜ)' den gelen akımla selenoid valfi açıp kapatarak silindire enjekte edilir. Bu döngü, enjektörün ömrü boyunca milyonlarca kez tekrarlanır. Yüksek basınçta defalarca tekrarlanan bu döngü sonucunda yakıttaki katı partiküller nedeniyle enjektör valfi aşınabilir ve valfin sızdırmasına neden olabilir. Bunun soncunda, enjeksiyon karakteristiği ve motor emisyon değerlerinde farklılıklar meydana gelebilir. Bosch geliştirme departmanı tarafından yapılan bir çalışmada, kaplaması kalkmış ve aşınmış valf gövdeleri ikinci bir dayanım testine sokulmuştur. Bu testin sonucunda, enjektörün temizlik seviyesinin değişmediği gözlemlenmiştir. Buna göre, oluşan bu aşınma geometrisinin valf gövdelerindeki kaplama uygulamasına alternatif olabileceği yorumu yapılmıştır. Bu tez çalışmasında, sıfır kilometre dizel enjektörlerde, kaplamasız valf parçalarının bilye oturma yüzeyine, küresel profil ile kuvvet uygulanarak yüzeyin deforme edilmesi ve bunun valf parçasının performansına olan etkisi incelenmiştir. Bu kapsamda, valfin fonksiyonel davranışını incelemek için bilgisayar destekli simülasyon çalışması yürütülmüştür. Simülasyon çalışması sonucuna istinaden, partikül ve kavitasyon davranışını incelemek için test çalışmaları tamamlanmıştır.
İleri kompozitlerin düşük sıcaklıklarda düşük hızlı darbe ve darbe sonrası bası davranışları
Composite materials are the general name given to materials created by a combination of two or more materials. Thermoset composites are resistant to high temperatures due to the strong covalent bonds between their chemical structures and are therefore used in many areas such as aviation, space and automobiles. Therefore, in this study, S2 glass / epoxy composite material was chosen to examine the low velocity impact and compression-after impact (CAI) behaviors. In this study, S2 glass/epoxy laminated composites were produced with a vacuum assisted resin infusion molding (VARIM) method. After that samples were prepared in dimensions of 100 mmx150 mm. First, impact tests were conducted at -50°C, -25°C and 20°C temperatures and 30 J, 40 J and 50 J impact energies for two different material thicknesses of 2.72 mm and 3.02 mm. Impact tests were performed by CEAST 9350 Fractovis Plus impact test machine. Then, impact behaviors were examined with the help of contact force-time and energy-time graphs. Impact damage photos of samples were given in figures. After impact tests, Compression-After Impact (CAI) test was applied to the samples at 20°C by Universal Shimadzu machine and a Boeing CAI fixture (ASTM D 7137) test apparatus. The effects of thickness, temperature and impact energy on CAI strength were examined. Impact and CAI damage photos of samples were also examined by visual inspection.
Doğal tekstil liflerinden üretilmiş dokuma kumaş takviyeli polimer kompozit malzemelerin darbe davranışlarının incelenmesi
The composite materials consist of least two materials. When the composites are compared with the metals and their alloys, they have many outstanding properties such as non-corrosion, high strength/weight ratio and ease of design. The fiber-reinforced composites are prevalently used in the industry. Generally, the synthetic fibers like carbon or glass usually were preferred. However, the synthetic fibers are hardly recycled in nature. Therefore, the natural fiber reinforced composites are begun to use as alternative in recent years. In this thesis, firstly, the flax fabrics were produced from the flax yarns by automated weaving machine in the different weft densities. After that, the flax woven reinforced composites were manufactured by vacuum assisted resin infusion molding (VARIM) method. Tensile, compression and shear tests were conducted to obtain modulus of elasticity, tensile and compressive strengths in warp and weft directions, Poisson's ratio, shear modulus and shear strength by Shimadzu tensile testing machine and test apparatus. Impact tests were carried out for different impact energies to obtain impact resistance and absorbed energy by CEAST Fractovis Plus impact test machine. Obtained results were compared according to the different yarn densities and it is seen that yarn density has a significant effect on mechanical properties, strengths and impact performance of the woven flax reinforced composites.
Sandviç kompozitlerin düşük hızlı darbe performansını geliştirmeye yönelik yapısal parametrelerin incelenmesi
Bu çalışmada, sandviç kompozitlerin düşük hızlı darbe performansının arttırılması amaçlanmıştır. Sandviç kompozitlerin, tabakalı kompozitlere göre eğilme rijitlikleri ve düşük hızlı darbe testinde absorbe ettiği enerji değerleri daha yüksektir. Ancak sandviç kompozitteki kabuk ve çekirdek malzemesi arasındaki yüksek dayanım farkından dolayı, birleşme arayüzeyinde yükleme anında ayrılma meydana gelebilmektedir. Sandviç kompozite çeşitli işlemler yapılarak düşük hızlı darbe testinde absorbe edeceği enerji değerinin arttırılmasına ve delaminasyon alanının azaltılmasına yönelik çalışmalar yapılmıştır. Sandviç kompozit yapılarda, iki çekirdekli hale getirme, epoksi kolonlar oluşturma, çekirdek dikiş işlemi, çekirdek ve kabukların birlikte dikiş işlemi uygulanmıştır. Bu kompozitlerin nümerik çalışma sonuçları ile deneysel çalışma sonuçları temas kuvveti - zaman eğrileri, temas kuvveti - çökme eğrileri ve absorbe edilen enerji değerleri kullanılarak karşılaştırılmıştır. Düşük hızlı darbe testinde vurucu kütlesi sabit tutulup, farklı enerjilerde düşük hızlı darbe testi yapılmıştır. Sandviç kompozitlerin düşük hızlı darbe davranışını etkileyecek çeşitli düzlem dışı takviye uygulamaları sayesinde, absorbe edilen enerji değerinde artış ve delaminasyon alanında azalış elde edilmiştir. Çekirdek dikiş işleminin absorbe edilen enerji değeri bakımından kabuk dikiş işlemine alternatif olabileceği tespit edilmiştir. LS-DYNA yazılımı kullanılarak yapılan sonlu elemanlar analizi sonuçları ile deneysel sonuçlar karşılaştırılmış ve iyi bir uyum görülmüştür.
Sandviç kompozitlerin onarım parametrelerinin incelenmesi
Bu çalışmada sandviç kompozitlerin onarım parametrelerindeki değişimin tamir sonrası mukavemete olan etkileri nümerik ve deneysel olarak incelenmiş, sonraki aşamada ise bu parametreler sabit tutularak tamir sonrası mukavemet değerlerini artırmaya yönelik yeni yama tipi çalışmaları gerçekleştirilmiştir. Geliştirilen yama yöntemlerinde temel yaklaşım, sandviç kompozitin hasarlı kısmının iç yüzeyine kompozit yapının bütünlüğünü bozmayacak şekilde fiber takviyesi yapılması ve yapılacak tamir işleminin kolay uygulanabilir olması olmuştur. Çalışma sonucunda sandviç kompozitlerin onarım parametrelerinin tamir sonrası mukavemete etkileri tespit edilmiş, yama kalınlığı ve bindirme uzunluğunun malzeme mukavemetine etkileri deneysel ve nümerik olarak gösterilmiştir. Sonuç olarak geliştirilen yeni yama yöntemleriyle tamir sonrası malzeme mukavemetinin önemli ölçüde arttırılması sağlanmıştır.
Tabakalı kompozit malzemelerin zımba kayma ve darbe davranışlarına termal etkiler
Composites are widely used in many applications thanks to their high strength-weight ratio. Transverse loading can cause serious damage to composite materials such as delamination, fiber breakage and matrix cracking. In this study, the thermal effects on punch shear and low velocity impact behaviors of laminated composite materials were investigated. The punch shear apparatus was fabricated in accordance with the previous researches and the quasi-static tests (QST) were performed by using Universal Shimadzu Tensile Testing Machine with the designed apparatus. Various speeds of crosshead as 1 mm/min., 10 mm/min., 20 mm/min, 40 mm/min and 60 mm/min were chosen for quasi-static tests. Low velocity impact (LVI) tests were carried out by using CEAST Fractovis Plus impact test machine at four different impact energies, 20J, 30J, 50J, and 80J. S2 glass/epoxy and hybrid carbon-kevlar/epoxy composite specimens with dimensions of 100x100 mm were used for both QST and LVI tests. Flat-nose and hemispherical nose impactors with a cylindrical punch diameter of 12.70 mm were mounted to the test machines. The tests were firstly performed at room temperature (23°C) and after with varied degree of temperature namely 40°C ,60°C and 80°C, in order to observe the effects of the temperature. After the experiments, the load-displacement graphs were plotted and the absorbed energy determined. The results of quasi-static punch shear test were compared to those of the low-velocity impact test and conclusion drawn.