Günümüzde arazi taşıtlarının performans hesabında kullanılan ampirik-analitik Bekker yöntemi, zaman ve maliyet isteyen çok sayıda deney yapılmasını gerektirmektedir. Bu yöntemde zemin özellikleri, basit basma ve basit kesme deneyi olarak adlandırılan iki yükleme deneyine dayanarak belirlenmektedir. Pratikte geniş kullanım alanı bulmuş olan bu model, ampirik-analitik yapısı nedeniyle ciddi eleştirilere konu olmuştur. Zemindeki gerilme-deformasyon ilişkisi basit bağıntılarla ifade edilemez. Zemin basınç altında hem elastik hem de plastik deformasyona uğrar. Gerilme ve deformasyon arasındaki ilişki hem yükleme hem de boşaltma esnasında nonlineer karakterdedir. Bu nedenle zeminin mekanik davranışı gerilme ve deformasyon arasındaki ilişkiyi temsil eden bünye denklemleriyle tanımlanmalıdır. Bu çalışma, paletli bir arazi taşıtının performansını kritik hal zemin mekaniği kavramlarından ve sonlu eleman yönteminden yararlanarak hesaplama hedefine yöneliktir. Performans hesaplarından önce basit basma ve basit kesme deneylerinin kuramsal-sayısal simülasyon modelleri oluşturulmuştur. Zeminin mekanik davranışının, kritik hal zemin özellikleri ile temsil edildiği bu modellerden yararlanılarak Bekker yaklaşımı ve kritik hal zemin mekaniği vasıtasıyla elde edilen sonuçlar arasındaki yakınsama araştırılmıştır. İki yaklaşımın ortaya koyduğu sonuçlar arasındaki benzerlik gözlenerek, Bekker katsayıları bilinen bir zemin tipi için kritik hal özellikleri tespit edilmiştir. Kritik hal özellikleri belirlenen zemin tipi üzerinde paletli bir arazi taşıtının yarattığı durumu yansıtan bir simülasyon oluşturulmuştur. Bu simülasyondan yararlanılarak bir M113 zırhlı personel taşıyıcısı paletinin, Detroit tını olarak sınıflandırılan bir zemin tipi üzerinde gösterdiği performans hesaplanmış, mevcut deney sonuçlarıyla karşılaştırılmış ve olumlu sonuçlar elde edilmiştir.

In spite of the rapid progress in technology, systematic studies on off-road vehicles did not receive significant attention until the middle of the twentieth century. The work of Bekker and other colleagues pointed out the engineers in the right direction to look at traction systems systematically. By using empirical and analytical methods Bekker could manage to develop a model to predict the performance value for motion resistance and net traction. Although there is a wide usage of Bekker’s method in practice, many investigators accept that there are some unnegligible shortcomings of this method. The most important one of them is that the mechanical behaviour of soil can not be expressed without using convenient constitutive equations. The empirical equations which are the basic descriptions of Bekker’s model are just mathematical expressions, which describe the change in the boundary conditions. Because the coefficients in these equations include the effect of the boundary conditions they can not reflect the soil properties independently. With the widespread availability of high speed computing facilities and powerful engineering software, coupled with recent advances in soil mechanics and computational methods, theoretical and numerical simulation of machine-soil interaction has become feasible. In soil mechanical applications, stressstrain models (or constitutive equations) provide necessary information to the finite element process for predicting stress propagation and the resulting soil deformations. The accuracy of the finite element predictions, therefore, depends on the accuracy of the constitutive equations of the soil. It is therefore important to identify which constitutive equations provide the most appropriate basis for finite element simulation. An important advance in soil mechanics is the development of the critical state soil mechanics as a theory, which allows us to determine the plastic deformation in soils within the limits of the theory of plasticity. The kernel of this theory is the concept that soil and other granular materials if continuously distorted until they flow as a frictional fluid, will come into a well-defined critical state. The critical state soil model is one step ahead than other ex isting soil stress-strain models because of its ability to represent the mechanical behaviour of soil accurately. The number of the parameters used in model implementation is a few. The physical meaning of these parameters is well defined and they are easy to measure. In this study the performance of a tracked vehicle is predicted via a theoretical and numerical simulation model based on critical state soil mechanics, instead of using the empirical and analytical methods. The interaction between the track and soil for a M113 armoured personal carrier is numerically simulated using a critical state soil model, implemented on a general purpose finite element program Tochnog. In empirical and analytical methods the soil properties are determined by two experiments, which are called as the simple pressure test and the simple shear test. Before modelling the track-soil interaction, finite element models which represent the simple pressure test and the simple shear test are developed. Critical state properties for soil are calibrated by watching the convergence between the results obtained from the empirical equations and from the finite element method. The performance of the track is presented as a function of slip and compared with available experimental data in the literature. The tests were performed on Detroit loam in two different moisture contents. In moist and medium wet loam the results of the Bekker model represent the upper bound of the data band at slip less than 10 percent. At slip greater than 10 percent the Bekker results overestimate the performance between 30 and 40 percent. The results of the theoretical and numerical simulation are in good agreement with experimental data. In moist loam they represent the upper bound of the data band at slip less than 5 percent. At slip between 5 and 18 percent they are in the data band. At slip greater than 18 percent the results represent the lower bound of the data band. In medium wet loam they represent the upper bound of the data band at slip less than 5 percent. At slip between 5 and 25 percent they are in the data band. At slip greater than 25 percent the results represent the lower bound of the data band