Paintings crack initiation time caused by microclimate

The current paper aims to use an irreversible cohesive zone model to investigate the effects of temperature and relative humidity cycles on multilayer thin-film paintings. The homogenous one-dimensional paint layers composed of alkyd and acrylic gesso over a canvas foundation (support) with known constant thicknesses are considered as the mechanical model of painting. Experimental data was used for mathematical modeling of canvas as a linear elastic material and paint as a viscoelastic material with the Prony series. Growth of crack through the length of the paint layers under the low amplitude cyclic stresses are modeled by cyclic mechanical loadings. The three-dimensional system is modeled using a finite element method. Fatigue damage parameters such as crack initiation time and maximum loads are calculated by an irreversible cohesive zone model used to control the interface separation. In addition, the effects of initial crack length and layers thickness are studied. With the increase of the painting thickness and/or the initial crack length, the value of the maximum force increases. Moreover, by increasing the Relative Humidity (RH) and the temperature difference at loading by one cycle per day, the values of initiation time of delamination decrease. It is shown that the thickness of painting layers is the most important parameter in crack initiation times and crack growth rate in historical paintings in museums and conservation settings.

Study on creep damage and crack growth for TC11 under complex stress loading

In order to investigate the creep damage and creep crack growth of TC11, we established the finite element model based on ductility exhaustion constitutive model. This paper uses the uniaxial creep test of TC11 at 500℃ as a reference and studies the effect of initial crack dimensions on crack growth of CT specimen and surface crack specimen. The initial crack length of CT specimen has a significant effect on creep crack growth of TC11 material. The larger the initial crack length, the higher the crack growth rate, the crack tip equivalent stress and the crack tip stress triaxiality. The initial crack length has a greater influence on creep crack growth for deep crack specimens(a0/W=0.6, a0/W=0.7) than that for shallow crack specimens(a0/W=0.3, a0/W=0.4, a0/W=0.5). When the stress intensity factor Kπ/2 at the deepest location of surface crack is the same, the crack growth length of each specimen in the depth direction at the same time is approximately twice as much as that in the length direction. With the increase of initial crack size, the crack growth rate of surface crack decreases gradually. And the effect of initial crack length on crack growth is greater than that of initial crack depth.

An approximate solution of compact test specimen for mode I fracture test by variational approach: Applied to fibrous composite

The present work presented an approximate solution for a compact test (CT) specimen that was employed as a standard test provided by ASTM E399-19 (2019). The variational method was employed to obtain the solution. The method used a two-step strategy to approximate the displacement response of the CT specimen. The first step was to obtain the general form of displacement solution, and then, the Rayleigh-Ritz approach was employed to modify the solution of the first step. A compliance equation of the CT specimen was obtained, and furthermore, the formula to calculate the stress intensity factor was obtained. The solution was validated by finite element (FE) model and the formula specified in ASTM E399-19 (2019). It was concluded that the calculation results of the proposed solution agreed well with the results of the FE model prediction for the ratio of initial crack length-to-ligament length, which was in the range of 0.25 to 0.35. Furthermore, compared to the results predicted by using the formula addressed in ASTM E399-19 (2019), the method proposed in the present study can achieve closer results than that of the FE model.

Reinforcement of Fatigue Damaged Steel Structures Using CFRP Lamellas – Part 3: Numerical Simulation/Verstärkung von ermüdungsbeanspruchten Stahlbauteilen mit aufgeklebten CFK- Lamellen – Teil 3: Numerische Simulation

ln two previous papers, CFRP reinforcements of fatigue damaged steel components were examined. For this purpose; CFRP lamellas glued on, either limp or pre-tensioned, were tested. The result of the reinforcement is an increased remaining service life. In order to understand the tests, numerical simulations with Abaqus based on XFEM were carried out in this paper. The simulations show (like the previous tests), in comparison with the unreinforced reference samples, a significant reduction in the stress on the crack tips through the application of CFRP lamellas. This shows the significantly longer remaining service life. ln addition, the parameter studies show that the remaining fatigue life is obviously influenced by the prestress, the stress range of cyclic loading, the initial crack length and the CFRP width.

Fracture of Parallel Strand Bamboo Composite under Mode I Loading: DCB Test Investigation

This paper describes the experimental studies on Mode I fracture of parallel strand bamboo (PSB) by the double cantilever beam (DCB) test. R-curves based on the elementary beam theory and specimen compliance are proposed in order to overcome the difficulties to monitor the crack propagation during experiments. The results demonstrate that the energy release rate (ERR) is influenced by the specimen geometry, i.e., the specimen width and initial crack length. The ERR at the plateau level is similar for the range of the analyzed widths (B = 20, 40, and 60 mm), while it decreases with width increasing up to 80 mm and 100 mm. The energy release rate for PSB specimens would verge to a stable value with the width increasing up to a specific value, while the value of the energy release rate will be influenced by the initial crack length. Consequently, the DCB tests also show that the obtained R-curve in this study is not a material property.

Behaviour of Damaged B.F.I. Beam Repaired by CFRP Strips under Static or Fatigue Loads Using Finite Element Simulation

This paper presents the numerical study to simulate the fatigue crack growth of artificially damaged steel Broad Flange I- beams section by single edge notched repaired with carbon fiber reinforced polymer CFRP strips. The study is carried out using ANSYS classic modeling approach is suggested to simulate the fatigue response of the beams, based on the cumulative damage theory and strain life method. Experimental test results were compared with FE results obtained. A parametric study was conducted using the validated model. The considered parameters were the number of CFRP strip layers used in the repair, the applied load range, initial crack length at time of strengthening and the thickness of CFRP strip. The numerical results indicated that the CFRP increased the critical crack length at which fracture occurred, and the strengthening was more effective at lower stress ranges. Moreover, the CFRP Strips can substantially delay failure and the results demonstrate the possibility of technique and highlight the importance of early intervention when repairing fatigue critical details. The ultimate load and ductility decreased substantially with increasing initial crack length at the time of installing the strengthening layer. Furthermore, increased capacity was achieved by increase the CFRP thickness and layers.