The Effect of Loading Rate on Fracture Toughness of Concrete using Type I Fracture Toughness Test Flattened Brazilian Disc (FBD) Mode

Mining activities in open pit and underground mines will always be associated with rock breaking or stripping activities (both mechanical and blasting), so that this can affect the structure and strength of rocks. The strength of the rock is strongly influenced by the presence of initial cracks (pre-existing cracks) and rock anisotropy conditions associated with discontinuous plane conditions. Fracture mechanics is a science that illustrates how a fracture can occur and propagate during applied stress on material. The main parameter in fracture mechanics is called fracture toughness which shows the resistance of the material to propagate the crack. There are several mode in determining type I fracture toughness, one of which is type I fracture toughness Flattened Brazilian Disc (FBD) mode. Type I fracture toughness test is carried out using a compression machine in a laboratory and is conducted on concrete samples consisting of 3 (three) various samples, with a ratio of cement and sand composition of 1:1, 1:2, and 2:1. This test also uses different loading rate values, namely 2.50 mm/min, 2.70 mm/min, and 2.83 mm/min. The results of the type I fracture toughness value from each loading rate will be compared to determine the effect of the loading rate on the value of type I fracture toughness. The obtained fracture toughness value is also related to the physical and mechanical properties of the samples. Based on the results of tests, it can be seen that the loading rate affects the value of fracture toughness, the increase in fracture toughness value is followed by the higher loading rate. In addition, it can be seen that the fracture toughness value is directly proportional to the uniaxial compressive strength value and the indirect tensile strength value. The average correlation value obtained is R2 = 0.9884 (indicating a strong relationship).

Comparative Study on Morphological, Physical and Mechanical Characteristics of L-PBF Based Alsi10mg Parts with Conventional Stir Casted Al-10%Sic Composites

Stir casting plays a major role in production of Al-SiC10% composites for aero space and automobile applications. However, obtaining the composites with homogenous distribution of the SiC particles, low porosity and without clustering of reinforcement particles were still a major problem faced by the research community. These kinds of casting defects were overcome by the Additive Manufacturing (AM) technology. In this research, AlSi10Mg parts were manufactured by Laser-Powder Bed Fusion (LPBF) method, one of the AM techniques. The mechanical and morphological characteristics of AM samples were compared with the Stir Casted (SC) samples. The influence of print orientation on the mechanical properties was also evaluated. It was found that the AM samples printed along the XY directions shows 26.5% and 8.2%higher fracture toughness and shear strength than AM samples printed along the Z directions. Both AM and SC samples were analyzed for the porosity% using the Optical Microscope (OM). The result shows that the AM sample shows reduced porosity of 1.4%. Mechanical testing such as tensile test, hardness test, fracture toughness test and double shear stress were carried out. The results obtained from the tensile test AM samples show 14.6% higher tensile strength than the SC samples, from the hardness test AM samples show 18.6% higher hardness strength than the SC samples, from the fracture toughness test AM samples show 33.4% higher fracture toughness strength than the SC samples and from the double shear stress test prove that the AM samples show 24.6% higher shear stress than the SC samples. The outcome of this research, it was proved that additive manufactured AlSi10Mgsample shows enhanced mechanical and morphological properties when compared with the conventional stir casting process.

Pipeline Steel Fracture Toughness and the Need for a Toughness Database of API 5L Line Pipe

In order for the pipeline industry to usher in the next-level fracture mechanics engineering analysis, reasonable and prudent fracture toughness characterizations are needed to improve burst pressure predictions and fatigue crack growth analysis of pipelines with planar cracks. Converting Charpy V-Notch (CVN) value to fracture toughness via different empirical correlation models derived throughout the years, while laudable, have inherent shortcomings. The main issues being that the Charpy toughness test is not a fracture mechanics-based measurement and the transferability of sub-scale fracture toughness testing is often not completely understood nor is correctly applied. This paper expands on these shortcomings and presents solutions which are supported by fracture toughness data obtained from the pipe boy and seam weld of API 5L line pipe steels. In this manner, best available toughness derivations for mean toughness in base metal and long seam welds are presented. Suggestions for standard fracture mechanics sub-scale coupon testing, such as ASTM E1820, on pipeline steel samples are delineated with rationale for each test type. The transferability of fracture toughness from sub-scale coupon testing results to that exhibits in full-scale pipe failure are demonstrated in the paper. This fracture toughness test database and other similar data sets can be combined and serve as the basis for establishing an industry wide Pipeline Material Database which would mirror established material databases in the aerospace industry such as NASGRO and AFMAT. It is envisioned that a centralized and validated Pipeline Material Database will be expanded to include fatigue crack growth rate data and other pipeline material characterization data sets. These data will support minimizing material assumptions and increase the accuracy of structural integrity predictions to improve the overall pipeline performance. This combined database would be accessible to engineers, analysts, and researchers and updated at regular intervals as more data becomes available.