TY - CONF A1 - Schilling, Markus A1 - Niebergall, Ute A1 - Böhning, Martin T1 - Failure of PE-HD induced by liquid media (ESC) N2 - As the well-known damage mechanisms slow crack growth (SCG) and environmental stress cracking (ESC) are the major causes for possible failure of polyolefin-based materials, especially for PE-HD, they are highly relevant and need to be considered thoroughly. Furthermore, due to slight but perceptible differences in damaging effect, a differentiation between SCG and ESC is expedient. SCG appears in “inert” or “neutral” media without a decisive influence of the surrounding medium whereas ESC occurs in “active” media, which influence the failure behavior and time to failure crucially. To characterize the inherent resistance of the material against those damage mechanisms, the well-established Full-Notch Creep Test (FNCT) is used. In this study, the FNCT – usually applied according to ISO 16770 [3] using a few universal model liquid media and mainly for pipe materials – is extended by investigations with appropriate parameters of selected relevant PE-HD container materials also in real media, such as the topical fuels diesel and biodiesel. The investigations were performed using a novel FNCT-device with 12 individual sub-stations, each equipped with individual electronic stress and temperature control and continuous online monitoring of the specimen elongation. Especially, mechanical stress and temperature were varied systematically during FNCT and time to failure values, time-dependent elongation data as well as detailed fracture surface analysis by laser scanning microscopy (LSM) were combined for the first time (Fig. 1). Particularly, the fracture surface analysis provides a sound basis to characterize failure behavior, mainly regarding the balance between brittle crack propagation and ductile deformation. Therefore, fracture surface analysis is an essential tool for a decent assessment of SCG and ESC by FNCT measurements. T2 - 17th International Conference on Deformation, Yield and Fracture of Polymers (DYFP) CY - Kerkrade, The Netherlands DA - 25.03.2018 KW - Environmental stress cracking (ESC) KW - PE-HD KW - Full Notch Creep Test (FNCT) KW - Imaging techniques KW - Brittle / ductile fracture behavior KW - Crack propagation analysis PY - 2018 AN - OPUS4-44617 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schilling, Markus A1 - Marschall, Niklas A1 - Niebergall, Ute A1 - Böhning, Martin T1 - An optical criterion for the assessment of Full-Notch Creep Test (FNCT) fracture surfaces N2 - The full-notch creep test (FNCT) is a common method to evaluate the environmental stress cracking (ESC) behavior of high-density polyethylene (PE-HD) container materials . The test procedure as specified in ISO 16770 provides a comparative measure of the resistance against ESC using the time to failure of specimens mechanically loaded in a well-defined liquid environment. Since the craze-crack damage mechanism underlying the ESC process is associated with brittle failure, the occurrence of globally brittle fracture surfaces is a prerequisite to consider an FNCT measurement as representative for ESC . Therefore, an optical evaluation of FNCT fracture surfaces concerning their brittleness is essential. Due to the experimental setup, an inevitable increase of the true mechanical stress and the associated appearance of small ductile parts on fracture surfaces is induced in any case. Hence, an FNCT experiment is considered as 'valid', if the corresponding fracture surface is predominantly brittle . Based on laser scanning microscopy (LSM) height data of FNCT fracture surfaces , a universal and easy-to-use phenomenological criterion was developed to assess the validity of distinct FNCT experiments. This criterion is supposed to facilitate a quick evaluation of FNCT results in practical routine testing. T2 - PPS Europe-Africa 2019 Regional Conference (PPS 2019) CY - Pretoria, South Africa DA - 18.11.2019 KW - Full-Notch Creep Test (FNCT) KW - Polyethylene, PE-HD KW - Fracture surface analysis KW - Environmental stress cracking (ESC) KW - Optical criterion KW - Brittle fracture PY - 2019 AN - OPUS4-50940 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schilling, Markus A1 - Niebergall, Ute A1 - Böhning, Martin T1 - Damage of PE-HD due to environmental stress cracking (ESC) induced by liquid media - Full Notch Creep Testing (FNCT) N2 - Due to the increasing demand for utilization and improvement of energy efficient materials, especially concerning requirements in lightweight construction and design, polyolefin materials are used extensively and in an increasingly broad range of applications. Although loaded with stresses under yield stress, preformed voids, inhomogeneities or notches can possibly lead to damage and unexpected failure induced by liquid media in polyolefin materials. For PE-HD, slow crack growth (SCG) as well as environmental stress cracking (ESC) are relevant mechanisms of damage. SCG appears without influence of a surrounding medium or in “inert” media whereas ESC occurs in “active” media, which have decisive influence on damage mechanism and time to failure. To characterize the intrinsic resistance of the material against those damage mechanisms, the Full-Notch Creep Test (FNCT) is widely used and of paramount importance particularly for the assessment of pipe and blow molding types of PE-HD. In this study, the FNCT – usually applied as a standardized testing method (ISO 16770) using a few universal model liquid media – is extended by investigations of selected relevant PE-HD materials with a variety of properties also in real media. Mainly topical fuels, customary in the market such as diesel and biodiesel are examined. Especially the influence of temperature, and the ESC behavior of PE-HD in media that are sorbed to a significant extent, are addressed. The underlying diffusion-controlled sorption process was assessed before comparing non-saturated specimens with samples previously saturated with sorbing media. The investigations were performed using a novel FNCT-device with 12 individual sub-stations, each equipped with individual electronic stress and temperature control and continuous online monitoring of the specimen elongation. In addition to acquired results concerning time to failure and elongation behavior, imaging techniques, such as light microscopy (LM), laser scanning microscopy (LSM) and X-ray computed tomography (CT scan) were utilized to obtain data concerning crack propagation and media migration. Fracture surface analysis (LM, LSM) and quasi in-situ imaging (CT scan) via measurement in different load stages are considered explicitly. Correlations of elongation behavior and data derived from imaging analysis such as fracture plane roughness and height of areas of ductile deformation were obtained. T2 - EUROCORR2017 CY - Prague, Czech Republic DA - 03.09.2017 KW - Environmental stress cracking (ESC) KW - Slow crack growth (SCG) KW - High-density polyethylene (PE-HD) KW - Full notch creep test (FNCT) KW - Biodiesel KW - Diesel PY - 2017 AN - OPUS4-43518 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schilling, Markus A1 - Niebergall, Ute A1 - Böhning, Martin T1 - Environmental stress cracking (ESC) of PE-HD induced by liquid media N2 - Due to the increasing demand for utilization and improvement of energy efficient materials, especially concerning requirements in lightweight construction and design, polyolefin materials are used extensively and in an increasingly broad range of applications. Although loaded with stresses under yield stress, preformed voids, inhomogeneities or notches can possibly lead to damage and unexpected failure induced by liquid media in polyolefin materials. For PE-HD, slow crack growth (SCG) as well as environmental stress cracking (ESC) are relevant damage mechanisms. SCG appears without influence of a surrounding medium or in “inert” media whereas ESC occurs in “active” media, which have decisive influence on damage mechanism and time to failure. To characterize the inherent resistance of the material against those damage mechanisms, the Full-Notch Creep Test (FNCT) is widely used. Therefore, the FNCT is of paramount importance particularly for the assessment of pipe and blow molding types of PE-HD – especially in the field of polymer development and improvement for high-performance applications. In this study, the FNCT – usually applied as a standardized testing method (ISO 16770) using a few universal model liquid media – is extended by investigation of selected relevant PE-HD materials with a variety of properties also in real media. Mainly topical fuels, customary in the market such as diesel and biodiesel are examined. Especially the influence of temperature, and the ESC behavior of PE-HD in media that are sorbed to a significant extent, are addressed. The investigations were performed using a novel FNCT-device with 12 individual sub-stations, each equipped with individual electronic stress and temperature control and continuous online monitoring of the specimen elongation. Additional to acquired results concerning time to failure and elongation behavior, imaging techniques, such as light microscopy (LM), laser scanning microscopy (LSM) and X-ray computed tomography (CT scan) were utilized to obtain data concerning crack propagation and media migration. Correlations of elongation behavior and data derived from imaging analysis were obtained. T2 - Europe / Africa Conference 2017 of the Polymer Processing Society (PPS) CY - Dresden, Germany DA - 26.06.2017 KW - Environmental stress cracking (ESC) KW - Full Notch Creep Test (FNCT) KW - High-density polyethylene (PE-HD) KW - Biodiesel PY - 2017 AN - OPUS4-43519 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -