Post Impact Tensile and Single Edge Notch Bending Test of Kenaf Hybrid Composite

The improvement of elite building items produced using regular assets is expanding around the world due to renewable and ecological issues. Among the wide range of characteristic assets, kenaf plants have been broadly abused in the course of recent years. The aim of this research is to develop long kenaf composites and long kenaf with woven glass reinforced polyester resin composites. Tensile test helps to determine how the material will react to forces being applied in tension. The test that was conducted included Post Impact Tensile test and Single Edge Notch Bend. Tensile test determines strain-stress while single edge notch bend determines the fracture of the specimen. The experiment was conducted using Universal Testing Machine (UTM) to find the mechanical properties. The experiment considered ASTM D3039 for tensile test and ASTM D5045 for single edge notch bending. From there, the damage area of the composites could be predicted. Meanwhile, it showed the best configuration for the newly developed material in impact test. So, these hybrid composites are viable to be extended into a newly developed material for further investigation

The influence of cell size on the mechanical properties of nanocellular PMMA

Solid-state foaming experiments are conducted on three grades of polymethyl methacrylate (PMMA). Nanocellular PMMA foams are manufactured with an average cell size ranging from 20 nm to 84 nm and a relative density between 0.37 and 0.5. For benchmarking purposes, additional microcellular PMMA foams with an average cell size close to 1 ìm and relative density close to that of the nanocellular foams are manufactured. Uniaxial compression tests and single edge notch bend tests are conducted on the PMMA foams. The measured Young's modulus and yield strength of the PMMA foams are independent of cell size whereas the fracture toughness of the PMMA foam increases with decreasing average cell size from the micron range to the nanometer range.

Reversing the Chell Model to Predict Using Monte Carlo Simulations the Original Fracture Toughness of Ferritic Steels

Warm pre-stress (WPS) is the process of subjecting a pre-cracked component to a load cycle at a temperature higher than subsequent operating temperatures. This process is widely acknowledged as being able to enhance the load to fracture, especially in ferritic steels which exhibit lower shelf cleavage fracture. Various models exist to predict this type of enhancement, with the Chell model being one of the most widely used within industry. Previous research conducted by Van Gelderen et al. have reformulated the Chell model to create a method of undertaking Monte Carlo Simulations (MCS) to study the effect of WPS on brittle fracture. Following on from this research, the Chell model could effectively be reversed providing a means of predicting the underlying fracture toughness from experimental WPS data. It also offers the possibility of assessing whether or not a specific specimen has indeed seen an enhancement, solely based on its experimental apparent toughness post WPS. The reverse Chell model was applied to different experimental data and provided reasonable estimates of the original fracture toughness. In the same way that the traditional Chell model offers conservative estimates, the reverse Chell model also provides “reverse conservative” estimates of the original fracture toughness. It was also used to provide confidence that a typical fatigue pre-cracking procedure performed according to ASTM standard E399 would not be sufficient to induce a WPS benefit on the specimens. This type of check can be of particularly interest when manufacturing small scale specimens (small scale Single Edge Notch Bend (SENB) or miniature sized Compact Tension C(T) specimens); a practice often favoured by industry to maximise the number of tests possible.

Development of Test Guidance for Single Edge Notch Bend Fracture Toughness Specimens Containing Notches Instead of Fatigue Pre-Cracks

Structural integrity assessment codes such as R6 and BS7910 provide guidance on the assessment of flaws that are assumed to be infinitely sharp. In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as lack of fusion, porosity or mechanical damage. Several methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. A common feature of these methods is the need to understand how the effective toughness, characterised using the J-integral for a notch, varies with notch acuity. No comprehensive guidance currently exists for obtaining J experimentally from specimens containing notches, hence the typical approach is to use equations intended for pre-cracked specimens to calculate J for notched specimens. This paper presents a comprehensive set of test guidance for calculating J from Single Edge Notch Bend (SENB) fracture toughness specimens containing notches instead of fatigue pre-cracks. This has been achieved using 3D Finite Element Analyses to quantify the accuracy of formulae intended for pre-cracked specimens in fracture toughness testing standards ASTM E1820, BS7448-1 and ESIS P2-92 when applied to specimens containing notches. The paper quantifies the accuracy of these equations for notched SENB specimens and identifies the conditions under which the equations can lead to inaccurate measurement of J for notched specimens.

Warm Pre-Stressing and Leaks in Pipelines

Line pipe steel is a carbon manganese steel. The toughness of line pipe steel undergoes a transition from high toughness (on the upper shelf) to low toughness (on the lower shelf) as the temperature decreases. A fluid will cool significantly as it expands through a leak in a pipeline. This has led to the suggestion that localised cooling of the material surrounding the leak might be sufficient to cool the material down to below the ductile to brittle transition temperature and cause a brittle fracture. Warm pre-stressing occurs when a load is applied to a structure containing a defect and then the temperature of the structure is reduced. Warm pre-stressing causes the defect in the structure to fail at a higher load at the lower temperature than if it had not experienced this prior loading at the previously higher temperature. A programme of single edge notch bend tests has been conducted on behalf of National Grid Carbon to demonstrate the beneficial effect of warm pre-stressing in a line pipe steel. The material tested was a sample of 914.4 mm outside diameter, 19.1 mm wall thickness, Grade API 5L X60 line pipe. Single edge notch bend specimens were subject to the ‘load-cool-fail’ cycle and the ‘load-unload-cool-fail’ cycle. The effect of different levels of stable ductile crack growth during the pre-load was also investigated. Warm pre-stressing is shown to have a beneficial effect. The load at failure in the specimens that had been subject to warm pre-stressing was higher than those that had not been subject to warm pre-stressing, and, in most cases, it was higher than the pre-load. The fracture toughness (in terms of the stress intensity factor) of the specimens that had been subject to warm pre-stressing was 1.4 to 1.7 times higher than that of those that had not been subject to warm pre-stressing. The results of the tests were conservatively predicted using the theoretical models. Also, the results are consistent with previous tests on structural steels. Therefore, localised cooling of the material around a leak in a pipeline is not predicted to result in a failure.

Numerical Estimation of JIC of a Ductile Metal

The paper presents a numerical technique to estimate the critical value of J integral, of a ductile metal (Aluminum alloy). Cracked, Single Edge Notch Bend (SENB) specimen of the alloy is modeled by finite element method. Load over the specimen is chosen such that the process or fracture zone is generated at the crack tip. The load is subsequently increased for the process zone size to go up. Process zone sizes and displacements under loads are measured from post processor solutions. Resistance curve and blunting line are plotted. Intersection of the two provides the value of. equals upon fulfillment of the plane strain condition. Various thickness values of the specimen are tried. The value of KIC obtained from is found to be in close agreement with the reported value obtained from experiments.Nomenclature