Spall experiment

Refs 1) J.S. Reinhardt, JApplPhys 22(5), 555-60(1950) (Some quantitative data bearing on the scabbing of metals under explosive attack) 2) K.B. Broberg, JApplMech 22, 317-23(1955) (Scabbing of solids under explosive attack) 3) E.B. Dally, "Spalling Experiments in Mild Steel , Poulter LaboratoriesIntRept 037-56(1956) 4) S. 

More general dynamic loading conditions can lead to more complex domains of tensile stress and spall. For example, in a Taylor impact experiment (Kipp and Davison, 1981), where a short cylinder of material is caused to undergo symmetric normal impact on the flat surface of a large block of material, a roughly spherical region within the cylinder is carried into dynamic tension and can undergo spall. 

Observations of smooth spalls in iron provided an early, dramatic demonstration of the importance of release wave behaviors. In 1956, Dally [61E01] reported the existence of remarkably smooth fracture surfaces in explosively compressed steel. The existence of these smooth spalls was a sensitive function of the sample thickness. Analysis and experiments by Erkman [61E01] confirmed that the smooth spalls were associated with interaction of release-wave shocks and shocks from reduction of pressure at free surfaces. These release shocks are a consequence of differences in compressibility at pressures just below and just above the 13 GPa transformation. 

Simple calculations of concrete structural fire resistance are not readily available. Above 300°C (572°F), the strength of concrete is reduced by 25% and should be discounted structurally (Spouge, 1999). Experiments on concrete slabs with hydrocarbon fires indicate that after 2 hours the outside 130 mm exceeds 300°C (572°F). Normally this concrete will spall away. 

Erkman describes in Ref 8a, experiments conducted at Poulter Labs, Stanford Research Institute, Menlo Park, Calif, in which A1 plates were caused to spall by explosively induced oblique shock waves. The work was principally directed toward developing techniques for performing reproducible experiments with A1 and for testing the scaling laws for spalling. During these experiments was also studied decay of explosively-induced shock waves in solids... 

Inhibition of filamentous carbon growth on metal surfaces by addition of titanium oxide has been reported previously (10). In these experiments the titanium oxide was in the fully oxidized state and was an effective physical barrier toward filament formation, provided that the temperature was kept below 920 K. Above this temperature, the oxide tended to spall, and as bare metal was exposed to the gas phase, prolific filament growth occurred. In the present study we have combined electron microscopy studies with... 

While most concrete defects occur as the result of flaws in design and installation, even good designs sometimes experience defects, earthquakes or similar events, freeze/thaw cycles, vapor/moisture permeability or overloading which lead to a need for repair. The floor should be checked periodically for cracks, spalling, bug holes, honeycombs, or other flaws. Where such flaws appear, they should be repaired and sealed. 

Figure 4. Damage distribution and mean stress contour plot at 2.0 ms in computer simulation of Experiment 79S. The contour level and plot dimensions are the same as in Figure 1. At this time, a layer of spall damage can be seen near the free surface. It developed as the tensile relief wave propagated downward following the interaction of the explosively generated shock with the free surface. This figure shows the final computed damage distribution.

The experiment will be carried out in Aspo diorite which is the typical rock type in the HRL. The unconfined strength of the rock is 219 MPa, the crack damage stress (CDS) 190 MPa, the crack initiation stress (CIS) 118 MPa, Nordlund (1999) and the tensile strength 14.8 MPa, Staub (2003). The laboratory deformation properties of the intact diorite are Young s modulus 68 GPa and Poisson s ratio, 0.24, (E=47 GPa was used in the sensitivity analysis). The tangential stresses required to initiate spalling are estimated to be approximately 150 MPa. The modelling results presented here have used the properties described above and an in-situ stress state of ai=30, 02=15... 

The Pillar experiment is specifically designed to monitor the brittle failure spalling process. This is a particularly difficult processes to simulate in numerical models as it requires the complete simulation of a rock mass transforming from a continuum to a discontinuum. The scoping... 

For this experiment a tunnel will be excavated at the 450 m depth. Two large holes with a diameter of 1.8 m and a depth of 6 m will be drilled in the tunnel floor to form a pillar with the width of 1 m. The loading configuration is designed to induce stresses in the pillar to a level close to spalling. 

Major objectives of the Aspo Pillar Stability Experiment are to demonstrate the capability to predict spalling in a fractured rock mass and to investigate the effect of the backfill (confining pressure) on the rock mass response. The FRACOD modelling aims to predict properly the fracturing process and the development of AE events during the planned sequences of excavation-confinement-heating. 

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