CTP kompozit profillerin darbe yükü etkisi altındaki davranışının sonlu elemanlar metodu ile incelenmesi
Investigating the behavior of GFRP composite profiles under impact loads using finite element method
Yazar: TUĞÇE ÇİMŞİR
Danışman: DOÇ. DR. ZEYNEP YAMAN ; DR. MOHAMMAD MANZOOR NASERY
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Bu tez çalışmasında, cam elyaf takviyeli plastik (GFRP) kompozit profillerin yapısal eleman olarak kullanılabilirliği, GFRP kompozit malzemenin profiller için uygunluğu ve darbe yüküne maruz durumlarda çelik malzemeye yeni bir alternatif olma potansiyelinin incelenmesi amaçlanmıştır. Bu kapsamda, kutu profil, I profil , U profil ve boru profil gibi farklı geometrik şekillere sahip profillerin darbe yükü altındaki davranışı sayısal olarak incelenmiştir. Lineer olmayan darbe analizleri Sonlu Elemanlar Yöntemi kullanılarak gerçekleştirilmiş ve bu analizlerde Abaqus programı kullanılmıştır. GFRP profiller ile çelik profillerin darbe yükü altındaki davranışlarını karşılaştırmak amacıyla, endüstride yaygın olarak kullanılan söz konusu profiller Fiberko firmasından alınan bilgiler baz alınarak analiz edilmiştir. Seçilen profillerin boyutları, endüstriyel bir üretim işletmesinin ürünleri referans alınarak belirlenmiş ve bu boyutlara göre hem GFRP hem de çelik malzeme olarak profiller Abaqus programında modellenmiştir. Belirlenen kutu profil, I profil, U profil ve boru profilleri modelledikten sonra, darbe yüklemesi 2000 mm yükseklikten 0,075 ton ağırlığına sahip rijit cismin serbest düşürülmesiyle gerçekleştirilmiştir. Darbe uygulanan cisim, deformasyon oluşmadan ve gerilme almaksızın bir rijit cisim olarak modellenmiş bununla birlikte profiller, boyutlarına göre deformasyona izin veren kabuk elemanlar olarak modellenmiştir. Geometrik modellere malzeme ataması yapılmış ve cam elyaf takviyeli (GFRP) malzeme için kullanılan elastik ve plastik malzeme özellikleri Abaqus programı kütüphanesinden alınmıştır. Cam fiber lifleri, profil kalınlığına göre eşit katmanlara bölünerek liflerin doğrultuları [0/-45/90/45/45/90/-45/0] olacak şekilde düzenlenmiştir. Sekiz farklı doğrultuda yönlendirilmiş cam fiber liflerinden meydana gelen kompozit malzemeye uygun malzeme ataması yapılmış ve profilin sınır şartları belirlenerek, biri sabit mesnet diğeri kayıcı mesnet olacak şekilde konfigüre edilmiştir. Rijit darbe cismi sadece düşey yönde hareket edebilecek şekilde sınırlandırılarak darbe analizi için rijit cisme hız tanımlaması yapılmış; 2000 mm yükseklikten serbest bırakılan ve 0,075 ton ağırlığındaki cismin düşme hızı, hesaplanarak 6264,18 mm/sn olarak belirlenmiştir. Bu değer, darbe analizi için kullanılmıştır. Sonlu eleman ağ boyutunun belirlenebilmesi amacıyla bir yakınsama çalışması gerçekleştirilmiştir. Analizlerde kullanılan profil üç farklı bölüme ayrılmış ve her bir bölüm için farklı sonlu eleman ağ boyutları denenmiştir. Bu çalışmanın sonucunda, profilin orta bölümünde en uygun sonlu eleman ağ boyutu olarak 5x5 mm belirlenirken, kalan bölgeler ve rijit darbe cismi için ise 15x15 mm boyutları tercih edilmiştir. Bu boyutlar, analizlerin doğruluğunu ve hesaplama stabilitesini sağlamak amacıyla seçilmiştir, böylelikle sonuçların güvenilirliği artırılmıştır. Malzeme farklılıkları ile birlikte çelik profiller ve GFRP kompozit profillerin arasında yapısal performans ve dayanıklılık açısından belirgin farklılıklar görülmüştür. Yapılan analizler, GFRP kompozit profillerin çelik profillere kıyasla daha elastik bir davranış sergilediğini ortaya koymuştur. Çelik profillerin genellikle daha az deplasman gösterdiği ancak kalıcı deformasyona daha fazla maruz kaldığı gözlemlenmiştir. Sonuç olarak, GFRP kompozit profillerin yer değiştirmeye karşı daha hassas olduğu ve bu malzemenin minimum mesnet reaksiyonu gerektiren yerlerde tercih edilebileceği, minimum deplasman ihtiyacı duyulan yerlerde ise çelik malzemenin tercih edilmesi gerektiği belirlenmiştir. Bu çalışma, yapısal gereksinimlere uygun malzeme seçiminin kritik bir öneme sahip olduğunu vurgulamakta ve darbe yüküne maruz kalacak yapılar için malzeme seçiminin titizlikle yapılması gerektiğini göstermektedir. Ayrıca, elde edilen sonuçlar arasında kompozit elemanların profil seçimi ve kalınlığının darbe davranışını etkileyen faktörler arasında olduğu da yer almaktadır.

Abstract:
This thesis aims to investigate the usability of glass fiber-reinforced plastic (GFRP) composite profiles as structural elements, assess the suitability of GFRP composite material for profiles, and evaluate its potential as a new alternative to steel. Within the scope of this thesis, impact analysis modeling was carried out for the profile types determined using the Abaqus program, which provides high-performance simulations, and the finite element method. To compare the impact behavior of GFRP and steel profiles, four different profile types commonly used in the industry were selected: box profile, I profile, U profile, and pipe profile. These profiles were modeled as GFRP and steel materials.  
Profile dimensions were determined using the products of an industrial production company, and the profiles were designed in Abaqus according to these dimensions. Following the design, impact tests were carried out by dropping a rigid object weighing 0.075 tons from a height of 2000 mm. In Abaqus, the rigid body was modeled as non-deformable, and the selected profiles with dimensions of 620550200 mm were modeled as shell elements that can be deformed according to their dimensions. Material assignments were made to the created geometric models, and elastic and plastic material properties for GFRP were obtained from the Abaqus program library. Glass fiber profiles are divided into equal layers with fiber orientations [0/-45/90/45/45/90/-45/0] according to profile thickness. Appropriate material assignment was made for the composite material consisting of glass fiber strips oriented in eight different directions. Boundary conditions were defined for the profile, with one end stable and the other end sliding. The hard impact body was constrained to move only in the vertical direction. For the impact analysis, the velocity of the rigid body was calculated as the free fall speed of the 0.075 ton object from a height of 2000 mm, resulting in a velocity input of 6264.18 mm/s.
In the finite element modeling, the profile was divided into three sections for mesh density. The middle section of the profile had a mesh size of 5 units, while the remaining sections and the rigid impact body were modeled with a mesh size of 15 units. Appropriate adjustment of the mesh size is important to obtain accurate analysis results, avoiding unnecessary complexity or oversimplification in the modeling process. 
Impact analysis was performed on steel profiles and glass fiber reinforced composite profiles (GFRD) to examine the behavior of these profiles under impact load. The results of the impact analysis were used to make a comparative evaluation between steel profiles and GFRP composite profiles. A total of eight impact tests were modeled on four different profiles using the Abaqus program and the finite element method. According to the impact analysis results of the box profile, the Von Mises stress distribution was determined as 411.040 MPa in the steel box profile, while this value was observed as 143.583 MPa in the GFRP box profile. At the moment of impact, the maximum Von Mises stress value was determined as 411.040 MPa in the steel profile and 925.207 MPa in the GFRP box profile. While Von Mises stresses under triaxial deformation continued after impact in the steel profile, it was observed that post-impact stresses were lower in the GFRP box profile. In addition to the plastic deformation distribution in the steel profile, the tensile and compression damage distributions of the fiber and matrix elements in the GFRP box profile were also observed. During the collision of the rigid object with the profile, displacements of 9.64 mm in the steel box profile and 22.32 mm in the GFRP box profile were detected. However, while permanent deformation was observed in the steel box profile after the impact, no permanent deformation was observed in the GFRP box profile. As a result of the impact load, a reaction force of 276.383 kN was obtained on stable and sliding supports in the steel box profile, and the force was calculated as 167.300 kN in the GFRP box profile model.
The support forces calculated in the GFRP box profile produced from composite material are smaller than those in the steel box profile. Although the acceleration value in the steel box profile is greater than that of the GFRP box profile, there is no significant difference between them. According to the U profile impact analysis results, it was determined that the Von Mises stresses calculated on the GFRP U profile and the Steel U profile were very similar to each other. However, it was observed that the Von Mises stresses calculated in the GFRP U profile were significantly larger than the stresses in the Steel U profile.  The maximum Von Mises stress was calculated as 483.149 MPa in the steel profile, whereas this value was determined as 1692.487 MPa in the GFRP profile. The maximum displacement analyzed in the elements in the center of the steel U profile is 10.31 mm, while the maximum displacement analyzed in the elements in the center of the GFRP U profile is 23.49 mm. After the impact, a reaction force of 244,510 kN was observed on the supports of the steel U profile, while a force of 135,509 kN was observed in the GFRP U profile model. The support forces calculated for the GFRP U profile produced from composite material were found to be lower than the Steel U profile, and at the same time, the acceleration value in the Steel U profile was found to be higher than the GFRP U profile. Regarding the I-profile impact analysis results, the Von Mises stress in the steel I profile is 408.507 MPa, and in the GFRP I profile, it is 97.276 MPa. The maximum Von Mises stress during the collision of the impact object with the profile were obtained 1507.216 MPa in the GFRP I profile and 418.680 MPa in the steel I profile. As the load was removed, the stresses in the GFRP profile decreased and approached the initial position, while post-impact stresses in the steel profile continued at similar values. The maximum displacement observed in the steel I profile is 7.75 mm, whereas the maximum displacement in the GFRP I profile is 16.67 mm.
The maximum support force is 326.331 kN in the steel profile and 184.906 kN in the GFRP profile. Steel I profile was exposed to more stress under impact load than GFRP I profile. After the impact, it was observed that the support forces in the steel profile were greater than the support forces in the GFRP profile. It was determined that the acceleration value of the steel I profile during impact was much higher than the GFRP I profile. According to the pipe profile impact analysis results, the maximum Von Mises stress during the impact was 488.797 MPa in the steel pipe profile and 1979.917 MPa in the GFRP pipe profile. After the impact, a stress of 399.086 MPa was observed in the steel profile and 1261.256 MPa in the GFRP profile. The maximum displacement observed in the steel pipe profile is 33.51 mm, while in the GFRP pipe profile the maximum displacement is 59.89 mm. While the maximum support force in the steel profile is determined as 53.587 kN, this value was measured as 29.837 kN in the GFRP profile. This revealed that the steel pipe profile was exposed to more stress under impact load than the GFRP pipe profile. It was observed that the acceleration value in the steel pipe profile at the moment of impact was greater than the acceleration value in the GFRP pipe profile. When the displacement, support response and acceleration values at the center of the profile modeled with GFRP material consisting of box profile, I profile, U profile and pipe profile are compared, the results are as follows; The U profile has a displacement of 23.49 mm, the I profile has a displacement of 16.67 mm, the box profile has a displacement of 22.32 mm and the pipe profile has a displacement of 59.89 mm. 
After the displacements that occurred during the impact, three profiles except the GFRP pipe profile were able to return to their original positions. However, the GFRP pipe profile suffered a permanent deformation of 3.5 mm due to the impact load. This results shows that the largest displacement during impact occurs in the pipe profile. Although the support reaction results obtained for I-profile, U-profile and box profile are similar to each other, the highest support reaction was calculated as 184.906 kN in the I-profile. The lowest support reaction value was obtained in the pipe profile. When the acceleration values calculated at the center of the profile were examined, it was observed that the GFRP pipe profile reached its maximum acceleration value. The lowest acceleration value was obtained in the GFRP I profile. When the displacement, support response and acceleration values at the center of the profile modeled with the steel material consisting of U profile, I profile, box profile and pipe profile are compared, the U profile has a displacement of 10.31 mm and the I profile has a displacement of 7.75 mm. mm, the box profile 9 is shifted by 0.64 mm, and the pipe profile is shifted by 33.51 mm. Following impact analysis, plastic deformation was applied to all steel profiles. This observation shows that the profiles change shape due to plastic deformation under impact.
The largest displacement during impact was observed in the pipe profile. The calculated maximum support force is 326.331 kN for I profile, 244.51 kN for U profile, 276.383 kN for box profile and 53.587 kN for pipe profile. While the maximum support reaction value was calculated for the I-profile, the lowest support reaction value was obtained for the pipe profile. When the acceleration values calculated at the center of the profile were examined, it was seen that the maximum acceleration value was reached in the U profile and the minimum acceleration value was reached in the pipe profile.
Material differences indicate significant differences in structural performance and durability between steel and GFRP composite profiles. In all impact analyses, maximum displacement results were obtained in glass fiber reinforced composite profiles, while maximum support reaction results were obtained in steel profiles. The results show that GFRP composite profiles exhibit a more elastic behavior than steel profiles and return to their original form more quickly after impact. Steel profiles generally showed less displacement but often exhibited permanent deformation. According to the analysis results, it was determined that GFRP composite profiles have advantages, especially in terms of corrosion resistance, but are more sensitive under impact loads and therefore are not preferred over steel profiles. The study emphasizes the critical importance of selecting materials that meet structural requirements and recommends the use of steel profiles in structures subjected to impact loads. It was concluded that especially GFRP pipe profiles are more sensitive to impact loads and should be taken into account in the selection process.