A consistent use of the Gurson-Tvergaard-Needleman damage model for the R-curve calculation

The scope of the present work is to point out a consistent simulation procedure for the quasi-static fracture processes, starting from the micro-structural characteristics of the material. To this aim, a local nineparameters Gurson-Tvergaard-Needleman (GTN) damage law has been used. The damage parameters depend on the micro-structural characteristics and must be calculated, measured or opportunely tuned. This can be done, as proposed by the author, by using an opportunely tuned GTN model for the representative volume element simulations, in order to enrich the original damage model by considering also the defect size distribution. Once determined all the material parameters, an MT fracture test has been simulated by a FE code, to calculate the R-curve in an aeronautical Al-based alloy. The simulation procedure produced results in a very good agreement with the experimental data

Cohesive law identification of adhesive layers subject to shear load The Twice Notched Flexure Test

Abstract By the means of a general analytic solution, suitable to identify the cohesive law that characterizes the behavior of adhesive layers subject to shear load and recently published by this author, a new test configuration is presented. This test configuration, named Twice Notched Flexure Test (TNF), is thought as alternative to the traditional End Notched Flexure (ENF) test or similar ones. It is expected to have several interesting improvement features. In order evaluating the TNF identification methodology, a de-cohesion virtual test is performed by means of detailed FE simulation. The simulation shows that, within the limits of the present model, the cohesive law can be deduced with very high precision

A consistent use of the Gurson-Tvergaard-Needleman damage model for the R-curve calculation

The scope of the present work is to point out a consistent simulation procedure for the quasi-static fracture processes, starting from the micro-structural characteristics of the material. To this aim, a local nineparameters Gurson-Tvergaard-Needleman (GTN) damage law has been used. The damage parameters depend on the micro-structural characteristics and must be calculated, measured or opportunely tuned. This can be done, as proposed by the author, by using an opportunely tuned GTN model for the representative volume element simulations, in order to enrich the original damage model by considering also the defect size distribution. Once determined all the material parameters, an MT fracture test has been simulated by a FE code, to calculate the R-curve in an aeronautical Al-based alloy. The simulation procedure produced results in a very good agreement with the experimental data

ON THE AFFERRANTE-CARBONE THEORY OF ULTRATOUGH TAPE PEELING

In a simple and interesting theory of ultratough peeling of an elastic tape from a viscoelastic substrate, Afferrante and Carbone find that there are conditions for which the load for steady state peeling could be arbitrarily large in steady state peeling, at low angles of peeling - what they call "ultratough" peeling (Afferrante, L., Carbone, G., 2016, The ultratough peeling of elastic tapes from viscoelastic substrates, Journal of the Mechanics and Physics of Solids, 96, pp.223-234). Surprisingly, this seems to lead to toughness enhancement higher than the limit value observed in a very large crack in an infinite viscoelastic body, possibly even considering a limit on the stress transmitted. The Afferrante-Carbone theory seems to be a quite approximate, qualitative theory and many aspects and features of this "ultratough" peeling (e.g. conformity with the Rivlin result at low peel angles) are obtained also through other mechanisms (Begley, M.R., Collino, R.R., Israelachvili, J.N., McMeeking, R.M., 2013, Peeling of a tape with large deformations and frictional sliding, Journal of the Mechanics and Physics of Solids, 61(5), pp. 1265-1279) although not at “critical velocities”. Experimental and/or numerical verification would be most useful

Cohesive fracture in composite systems: experimental setup and first results

Composite systems are widely used in many engineering applications for new structures and strengthening of existing ones. Within the structural rehabilitation of civil constructions, the plating technique of beams with Fiber Reinforced Polymer (FRP) represents a quick and optimal intervention with respect to traditional ones. The failure of these composite systems usually occurs due to the FRP debonding, which corresponds to a mode II fracture of concrete specimens. In this paper, a new experimental setup for investigating the mode II fracture behavior of FRP-concrete composite structures is presented. The test equipment consists of both conventional equipment and a non-contact optical technique, Digital Image Correlation (DIC), and the test system was realized at the Design Machine Laboratory of the University of Salerno. A preliminary test was performed and the corresponding results are shown and discussed

Cohesive fracture in composite systems: experimental setup and first results

Composite systems are widely used in many engineering applications for new structures and strengthening of existing ones. Within the structural rehabilitation of civil constructions, the plating technique of beams with Fiber Reinforced Polymer (FRP) represents a quick and optimal intervention with respect to traditional ones. The failure of these composite systems usually occurs due to the FRP debonding, which corresponds to a mode II fracture of concrete specimens. In this paper, a new experimental setup for investigating the mode II fracture behavior of FRP-concrete composite structures is presented. The test equipment consists of both conventional equipment and a non-contact optical technique, Digital Image Correlation (DIC), and the test system was realized at the Design Machine Laboratory of the University of Salerno. A preliminary test was performed and the corresponding results are shown and discussed

Colorectal Cancer Stage at Diagnosis Before vs During the COVID-19 Pandemic in Italy

IMPORTANCE Delays in screening programs and the reluctance of patients to seek medical attention because of the outbreak of SARS-CoV-2 could be associated with the risk of more advanced colorectal cancers at diagnosis. OBJECTIVE To evaluate whether the SARS-CoV-2 pandemic was associated with more advanced oncologic stage and change in clinical presentation for patients with colorectal cancer. DESIGN, SETTING, AND PARTICIPANTS This retrospective, multicenter cohort study included all 17 938 adult patients who underwent surgery for colorectal cancer from March 1, 2020, to December 31, 2021 (pandemic period), and from January 1, 2018, to February 29, 2020 (prepandemic period), in 81 participating centers in Italy, including tertiary centers and community hospitals. Follow-up was 30 days from surgery. EXPOSURES Any type of surgical procedure for colorectal cancer, including explorative surgery, palliative procedures, and atypical or segmental resections. MAIN OUTCOMES AND MEASURES The primary outcome was advanced stage of colorectal cancer at diagnosis. Secondary outcomes were distant metastasis, T4 stage, aggressive biology (defined as cancer with at least 1 of the following characteristics: signet ring cells, mucinous tumor, budding, lymphovascular invasion, perineural invasion, and lymphangitis), stenotic lesion, emergency surgery, and palliative surgery. The independent association between the pandemic period and the outcomes was assessed using multivariate random-effects logistic regression, with hospital as the cluster variable. RESULTS A total of 17 938 patients (10 007 men [55.8%]; mean [SD] age, 70.6 [12.2] years) underwent surgery for colorectal cancer: 7796 (43.5%) during the pandemic period and 10 142 (56.5%) during the prepandemic period. Logistic regression indicated that the pandemic period was significantly associated with an increased rate of advanced-stage colorectal cancer (odds ratio [OR], 1.07; 95%CI, 1.01-1.13; P = .03), aggressive biology (OR, 1.32; 95%CI, 1.15-1.53; P < .001), and stenotic lesions (OR, 1.15; 95%CI, 1.01-1.31; P = .03). CONCLUSIONS AND RELEVANCE This cohort study suggests a significant association between the SARS-CoV-2 pandemic and the risk of a more advanced oncologic stage at diagnosis among patients undergoing surgery for colorectal cancer and might indicate a potential reduction of survival for these patients

Cohesive law identification of adhesive layers subject to shear load – An exact inverse solution

An exact general solution of the following inverse problem is obtained: given a couple of beams adhe- sively bonded along a surface parallel to their axes, subject to traction / flexure load, find the unknown interface shear force. This solution is used to identify the cohesive law that characterizes the behaviour of adhesive layers subject to shear load. In order to generate data to be used to evaluate the identifica- tion methodology, three decohesion virtual tests are performed by means of detailed FE simulations. The series of tests is related to standard test configurations, and shows the correctness of the inverse solution and the efficiency of the proposed methodology, as it is more precise than the data reduction method- ologies provided by literature. If ad hoc test configurations are designed, this identification methodology can be applied to adhesion between different materials and to adhesive layers with variable behaviour