Düşen yükten etkilenen malzemenin şekil değiştirmesinin deneysel ve sayısal analiz metoduyla incelenmesi
Investigation of the deformation of the material affected by the drop load by experimental and numerical analysis method
Yazar: GÜRKAN YILMAZ
Danışman: DOÇ. DR. ERTEKİN BAYRAKTARKATAL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Gemi İnşaatı ve Gemi Makineleri Mühendisliği Ana Bilim Dalı / Gemi İnşaatı ve Gemi Makineleri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Gemi Mühendisliği = Marine Engineering
Dizin: Gemi inşaatı endüstrisi = Shipbuilding industry ; Malzeme davranışı = Material behavior

Özet:
Deniz yapıları çarpma, çalkantı gibi dış kuvvetler haricindeki bazı operasyonlar sırasında meydana gelebilecek dinamik basınç yüklerinden muzdarip olmaya meyillidir. Gemi inşaatında çelik ve alüminyum yapıların darbe direncini iyileştirmek için maruz kalacağı dinamik etkinin ayrıntılı bir biçimde incelenmesi elzemdir.
Bu araştırma, belirli yükselikten bırakılan kama biçimindeki katı cismin alüminyum plakalar üzerindeki çökme miktarını gözlemleme üzerinedir.
Araştırma, deneysel, analitik ve sonlu eleman analiz programı vasıtası ile üç ayrı biçimde sonuca ulaştırılmış, ortaya çıkan veriler kaydedilerek birbiri ile kıyaslanmıştır. 
Deney materyalleri olarak, alüminyum plaka, serbest düşüş mekanizması, kuvvet ölçüm sensörü, ivme sensörü, kaynakçı kumpası, 3d yazıcı ve bilgisayar destekli bir takım programlar kullanılmıştır. 
Deneysel araştırma aşamasında, serbest düşüş ile bırakılan kamanın ağırlığı belirli aralık içerisinde artırılarak alüminyum lamalar üzerindeki çökme miktarı kaynakçı kumpası yardımıyla ölçümlenmiştir.
Oluşturulan sistem matrisine göre tekrarlanan deneylerden alınan veriler ilgili matris düzenince kayıt edilmiştir. İlgili sistem matrisi sonlu eleman analiz programı yardımıyla modellenerek program üzerinde deneyler tekrarlanmıştır. Bu iki kısımdan elde edilen sonuçlar karşılaştırılarak aradaki fark gözlemlenmiştir.
Ayrıca şok faktörü metodu olarak literatürde yer alan ve dinamik kuvvetler etkisindeki malzemenin sehiminin analitik olarak hesaplanmasını sağlayan teknik yardımıyla ek bir hesaplamada bulunulmuştur. Alınan sonuçların deney ve analiz verileriyle tam olarak örtüşmediği tespit edilmiştir. 
Deney boyunca düşürülen yüklerin düşürülme yüksekliği sabit tutulmuştur. Deneyde yalnızca düşürülen kama cisminin ağırlığı değiştirilmiştir. Deney düzeneğinin makaralı sistem olarak tasarlanması nedeniyle kamanın ağırlığının azaltılması için sistem ağırlığının artırılması gerekmektedir. Bu sebeple kama cisminin ağırlığı değiştikçe sahip olduğu ivme de değişime uğramıştır. İvme değerinin değişmesi kamanın deney ürününe çarptığı andaki hız değerini değiştirmiş ve böylelilikle tesir eden net kuvvet miktarının beklenilenden daha farklı olmasına sebebiyet vermiştir. İvme sensörü sayesinde deney süresince kamanın sahip olduğu ivme değerlerine erişilmiştir. Kamanın sahip olduğu ivme değerleri ve zamansız hız denklemi vasıtasıyla kamanın lamaya çarpma anındaki hız değerleri saptanmıştır. Bu metod vasıtasıyla tüm deneyler için gerekli olan hız değerlerine erişilmiştir. Sayısal analiz kısmında kamanın lamaya temas ettiği aşamada bu hız değerleri kama üzerine uygulanarak deney düzeneğinin analiz programındaki simulasyona tanımı gerçekleştirilmiştir.
Bu çalışmanın amacı, malzeme üzerinde meydana gelen dinamik kuvvetin oluşturacağı çökme miktarının deneysel olarak incelenmesi ve sayısal analiz metoduyla hesaplamada bulunarak sonuçların karşılaştırılmasına dayanmaktadır. Bu çalışmanın sonucunda kapsamlı olarak hazırlanacak bir dinamik analiz simulasyonunun gerçek verilerle ilişkisi konusunda kayda değer veriler ortaya konmuştur.

Abstract:
Marine structures tend to be subjected to dynamic compressive loads that may occur during some operations other than external forces such as impact and turbulence. In order to improve the impact force resistance of steel and aluminum structures in shipbuilding, a detailed study of the dynamic response is essential.
This research is focused on observing the amount of collapse on aluminum plates of a rigid wedge-shaped object dropped from a certain height.
Initially, the deformation properties and types of materials are mentioned. The beam theorem and methods for calculating the amount of collapse of the beam are added. Similar studies are reviewed and presented in a separate section as literature information.
The research was concluded in three different ways: experimental, analytical and finite element analysis program and the data obtained were recorded and compared with each other. Aluminum plate, free fall mechanism, force measurement sensor, acceleration measurement sensor, welder caliper, 3D printer and some computer aided programs were used as experimental materials. 
In the experimental research phase, the weight of the wedge released by free fall was increased at a certain interval and the amount of collapse on the aluminum samples was measured with the help of a welder's caliper.
The data obtained from repeated experiments according to the system matrix was recorded in the relevant matrix layout. The relevant system matrix was modeled with the help of a finite element analysis program and repeated on the program. The results obtained from these two parts were compared and the difference was observed.
Since it is desired to subject the specimen to permanent deformation in the experiment, experimental and analysis studies were developed on the behavior of the material in the plastic region. Since it would be very difficult to obtain experimental data in the elastic region due to the return of the material to its original form, it was decided to work on the plastic region and the specimens were subjected to permanent deformation.
In this study, the type of specimen used during the experiment is of great importance. For this reason, it was decided to choose AL5083 aluminum material, which is widely used in the shipbuilding industry, for the experiment in consultation with leading metal fabrication companies. All specimens were prepared by cutting the same dimensions from a single large plate. In this way, it was ensured that all materials had the same properties and the test results were consistent.
As a finite element analysis program, the Abaqus program, which is considered to best simulate a material under dynamic load, was preferred. Abaqus program has the ability to simulate material properties in the most realistic way. For this reason, in order to obtain more realistic data, the correct material definitions were included in the Abaqus program by conducting literature research. For this purpose, the use of Johnson-Cook material parameters was preferred. In addition, a certain coefficient of friction was added between the specimen and the steel plate on which it was placed in free position based on the data available in the literature. For the interfacial interactions, a friction coefficient of 0.2 was entered between the aluminium plate and the support elements.
In order to apply the correct mesh definition to the structure modeled in the analysis program, some research has been carried out. As a result of the information obtained, it was decided to use C3D8R type mesh. In order to provide the correct element size for the mesh, a few preliminary test analyzes were performed. As a result, it was observed that the collapse difference remained below the measurable value for element sizes below 5 mm. For this reason, it was decided to use an element size of 5 mm for the mesh.
This study also presents the details of the Abaqus program and the hierarchy considered in the program during the modeling of the experiment. Suggestions are made about the errors that may be encountered in the program and the situations that should be considered.
In addition, an additional calculation was performed with the help of a technique known in the literature as the shock factor method, which allows the deflection of the material under the influence of dynamic forces to be calculated analytically. It was determined that the results obtained did not fully coincide with the experimental and analysis data. 
The drop height of the falling loads was kept constant throughout the experiment. Only the weight of the dropped wedge object was changed in the experiment. Since the experimental setup was designed as a roller system, it was necessary to increase the system weight to reduce the weight of the wedge. Therefore, as the weight of the wedge object changed, its acceleration also changed. The change in the acceleration value changed the velocity value at the moment when the wedge hit the test specimen, thus causing the net force to be different than expected. With the help of the acceleration measuring device, the impact velocity was obtained according to the acceleration and time data obtained from the test specimen, and with the help of this velocity. In the numerical analysis part, these velocity values were defined to the wedge for the step where the wedge contacts the specimen.
Many different methods and measurement techniques were tried in the experimental phase. During the tests on the first test product, the force sensor broke and the experiment was continued with the help of an acceleration sensor.
Before the failure of the force sensor, the wedge weight was measured by means of this sensor for all experiments. Although the weight was initially measured with the help of a simple scale, it was considered that this approach would not be sensitive enough and the force sensor was used for wedge weight measurements.
The aim of this study is based on the experimental investigation of the amount of collapse caused by the dynamic force on the material and the comparison of the results by numerical analysis method. As a result of this study, significant data on the relationship of a comprehensive dynamic analysis simulation with real data has been presented.
In the future, by conducting different experimental studies similar to this research, more information can be obtained about the behaviour of general materials used in the marine industry. In the light of this information, it can be possible to create simulations closer to reality. With the help of this study, information about the behaviour of a material under dynamic force has been obtained and it has been observed that the analysis results are very close to the real data. In this direction, it can be said that a structure similar to the scenario in this study in real life can be taken as a basis for the preliminary design phase with the use of certain safety coefficients.