The paper discusses the influence of the initial parameters on the strength parameters of S235JR steel at low stress triaxiality. The analysis was performed using the Gurson-Tvergaard-Needlem (GTN) material model, which takes into consideration the material structure. The initial material porosity was defined as the void volume fraction f₀. The fully dense material without pores was assumed and the typical and maximum values of porosity were considered for S235JR steel in order to analyse the porosity effect. The strength analysis of S235JR steel was performed basing on the force-elongation curves obtained experimentally and during numerical simulations. Taking into consideration the results obtained, the average values of the initial void volume fraction f₀ = 0.001 for S235JR steel is recommended to use in a common engineering calculations for elements operating at low stress triaxiality. In order to obtain more conservative results, the maximum values of f₀ = 0.0024 may be used.

The effect of the initial porosity on the material response under multi-axial stress state for S235JR steel using the Gurson-Tvergaard-Needleman (GTN) material model was examined. Three levels of initial porosity, defined by the void volume fraction f₀, were considered: zero porosity for fully dense material without pores, average and maximum porosity according to the metallurgical requirements for S235JR steel. The effect of the initial porosity on the material response was noticed for tensile elements under multi-axial stress state defined by high stress triaxiality σₘ/σe = 1.345. This effect was especially noticeable at the range of the material failure. In terms of the load-bearing capacity of the elements, the conservative results were obtained when maximum value of f₀ = 0.0024 was used for S235JR steel under multi-axial stress state, and this value is recommended to use in the calculations in order to preserve the highest safety level of the structure. In usual engineering calculations, the average porosity defined by f₀ = 0.001 may be applied for S235JR.

This paper deals with problems of failure mechanisms of S235JR structural steel. One of the fundamental parameters of the Gurson-Tvergaard-Needleman damage mechanics-based material model is considered in order to describe the behaviour of the material at the plastic range. The analysis was performed on the void volume fraction f_F determined at failure of S235JR steel. The case of low initial stress triaxiality η = 1/3 was taken into consideration. Different from the most popular methods such as curve-fitting, the experimental method based on the digital image analysis of the fracture surface of S235JR steel is proposed in order to determine the critical parameter f_F.

This paper presents the results of the static work analysis of laminated veneer lumber (LVL) beams strengthened with carbon fabric sheets (CFRP). Tested specimens were 45mm wide, 100 mm high, and 1700 mm long. Two types of strengthening arrangements were assumed as follows: 1. One layer of sheet bonded to the bottom face; 2. U-shape half-wrapped reinforcement; both sides wrapped to half of the height of the cross-section. The reinforcement ratios were 0.22% and 0.72%, respectively. In both cases, the FRP reinforcement was bonded along the entire span of the element by means of epoxy resin. The reinforcement of the elements resulted in an increase in the bending strength by 30% and 35%, respectively, as well as an increase in the global modulus of elasticity in bending greater than 20% for both configurations (in comparison to the reference elements).

The article discusses the basic issues related to the technology of friction stir welding (FSW). A short description of technology is provided. The following section provides the analysis of effect of technological parameters (tool rotation and welding speed) on the mechanical properties of the prepared joint (strength, ductility, microhardness). In both cases the analysis refers to aluminum alloys (6056 and AA2195-T0). The comparative analysis showed the phenomenon of the increase in weld strength along with the increase in the rotational speed of the tool during welding. Similarly, with the increase in welding speed, an increase in weld strength was observed. Some exceptions have been observed from the above relations, as described in the article. In addition, examples of material hardness distribution in the joint are presented, indicating their lack of symmetry, caused by the rotational movement of the tool. The analyses were performed basing on the literature data.

The article discusses results of pull-off adhesion strength tests on poly-p- phenylene benzobisoxazole (PBO) mesh bonded to fir timber beams using epoxy resin. The tests were performed in accordance with the PN-EN 1542 standard. Timber elements reinforced with PBO fibres were subjected to pull-off tests to measure the adhesive strength of the mesh to the beams.The factors occurring during the test were also characterized, which may affect its results such as the method of application of the tearing force, selection of epoxy glue, surface preparation of the tested elements, occurrence of material defects in the wood and types of substrate destruction.The experimental data show that failure of the timber layer was not observed in all the specimens tested.

This paper presents the results of preliminary tests for estimating the modulus of elasticity of wooden beams from firs reinforced with PBO fiber mesh. The tests were carried out in the Materials Strength Laboratory at the Kielce University of Technology in Kielce, Poland with PN-EN 408:2004. The wooden elements were subjected to a four-point bending test with the aim of estimating the elastic modulus when bending, assuming the loading velocities of the loading forces of 5 mm/min. The obtained results show a significant increase in the load-bearing capacity of beams reinforced with PBO mesh.