A variety of materials are used as elements and constructions in many branches of industry. These materials are exposed to heavy variable mechanical and thermal loads during service. The resultant stresses of variable thermal and mechanical loads are added and they may reach high levels in the stress concentration regions of the elements, leading to the formation of cracks. In this study, the formation of thermal stress concentrations was investigated using photothermoelastic models for butt-jointed thick plates from different materials at the weld zone. In the models, the effect of the slope of the materials' connection plane with respect to the normal plane of the plate on the stress distribution was studied. In the stress concentration regions of the considered joints, the effect of the different geometric factors was also investigated on the models in order to arrange the concentration of the thermal stresses as required.