Crushing Behavior and Crushing Strengths of Low-Density Foam Concrete

Foam concrete is a highly cellularized cementitious material that undergoes extensive plastic deformation when loaded to failure. Under compression, the foam structure gets progressively crushed at a steady stress stage such that a substantial amount of energy is dissipated. Understanding foam concrete crushing behavior is of special importance for its engineering applications such as energy absorber, but the current studies are insufficient to define material properties for design of field applications. This study characterizes the crushing strength and foam modulus of samples with penetration test and resonant frequency test, respectively. A four-phase crushing behavior is observed. The yield strength and plateau strength are identified to characterize the foam crushing. Using the experimental inputs, the modulus-strength constitutive equations are then established. These findings are useful for expanding the knowledge of normal concrete to studies on foam concrete, as well as design of applications.Foam concrete is a highly cellularized cementitious material that undergoes extensive plastic deformation when loaded to failure. Under compression, the foam structure gets progressively crushed at a steady stress stage such that a substantial amount of energy is dissipated. Understanding foam concrete crushing behavior is of special importance for its engineering applications such as energy absorber, but the current studies are insufficient to define material properties for design of field applications. This study characterizes the crushing strength and foam modulus of samples with penetration test and resonant frequency test, respectively. A four-phase crushing behavior is observed. The yield strength and plateau strength are identified to characterize the foam crushing. Using the experimental inputs, the modulus-strength constitutive equations are then established. These findings are useful for expanding the knowledge of normal concrete to studies on foam concrete, as well as design of applications.

Evaluation of Matrix and Geometric Strain Hardening of Axial Deformed Sintered Fe-0.75%C Preform

Strain hardening occurs as a result of extensive plastic deformation of a material at below recrystallization temperature. The powder metallurgy route subjects the elemental powders to highly plastic deformation under compaction; however it is softened while it is sintered. In order to enhance its mechanical behaviour, it is usually subjected to secondary deformation operation. In the present investigation the cold upsetting exercise is carried out in three different lubricants condition with two different preform geometries on sintered Fe-0.75%C. Unlike the conventional material under plastic deformation the matrix gets strain harden, in P/M material along with matrix the geometry supplements the strain hardening behaviour. The nature of matrix and geometric hardening behaviour has been dealt. In addition an empirical relationship and its corresponding parameters experimental values have been predicted which is of high importance in design of preforms and die-set for actual production.

THE INFLUENCE OF MATERIAL MICROSTRUCTURE ON THE CHIP FORMING PROCESS

For a number of alloys the process of metal cutting is accompanied by extensive plastic deformation and fracture. In the paper we investigate quick stop samples of the chip formation of materials with different chemical composition and microstructure. The type of chip formation is classified according to the mechanism of crack formation and propagation. During cutting, most samples that are used, quasi-continuous chips with built-up edge (BUE) are obtained. The formation of BUE is undesirable since it is a highly deformed body with a semi stable top which periodically breaks away giving rise to poor workpiece surface quality.

Texture, Grain Boundaries, Defects and Location of Substitutional Atoms in Cryo-Mechanically Processed Ti-5Ta-1.8Nb Alloy

An α-β alloy (β~8% in the stress relieved condition) of Ti-5Ta-1.8Nb has been subjected to severe plastic deformation (SPD) by cryo-rolling. The grain size of α-Ti could be reduced significantly from ~ 8µm to 100 nm and less by cryo-rolling. Extensive plastic deformation leads to grain fragmentation through the formation of defect clusters. The fragmented grains exhibit deformation texture. High resolution transmission electron microscopy (HRTEM) confirmed the presence of low and high angle grain boundaries. The role of substitutional atoms (Ta, Nb) in producing lattice strains and altering the projected potential from the atomic columns has been discussed. Although, the minor phase, β (bcc-Ti) is evident in the starting alloy, it was not observed after SPD, possibly due to extended solid solution formation (Gibbs–Thomson effect) in the fine grains or due to the stress induced transformation of the α-Ti phase.

Wear Behaviors of TiCN Cermet under Different Concentrations of Abrasive Slurries from Carborundum, Corundum and Silica Sands

Through a modified ASTM B611 wet sand rubber rimmed wheel test system (model: MLS-225), the wear resistance of commercially bought TiCN cermets FD22 was studied with water-based slurries of abrasive sands. The applied abrasives were angular sands of carborundum, corundum, and silica with particle size of about 350 μm. During experiments, the rotation speed of the rubber wheel was fixed at 498 rpm, and the load was 225 N. The results show that with increasing concentration of abrasive sands in the slurry, the wear loss of the cermet samples increased. Under the same conditions, when carborundum was used as abrasive, the cermet samples presented the heaviest wear loss and the highest wear rate, but when silica was used as abrasive, the cermet samples presented the slightest wear loss and the lowest wear rate. Under the abrasive concentrations of 5-20 wt% in slurry, the wear rate remained almost unchanged as the sliding distance increased. However, when the concentration was higher than 20 wt%, as the sliding distance increased, the wear rate increased at first and gradually decreased with the sliding distance over 30 km. Through the observations of 3D white-light interfering surface profiler, it was found that the wear mechanisms of TiCN cermet samples involved in extensive plastic deformation, grooves, binder removal and fracture.

Wear Behaviors of Cemented Carbide Cermet YG8B under Different Concentrations of Abrasive Slurries from Carborundum, Corundum and Silica Sands

This work investigated the wear behavior of cemented carbide cermet YG8B under different concentrations of abrasive slurries using a modified ASTM B611 wet sand rubber rimmed wheel test system with a load of 225 N. The angular sand abrasives involved in carborundum, corundum and silica with particle size of about 350 μm, and were dispersed into water with different mass fractions. It was found that, with increasing sand concentration in slurry, the wear loss of the cermet samples increased, and with the increase of duration time, the wear loss of the cermet samples also increased. Under the same conditions, the cermet samples presented the biggest wear loss with carborundum as abrasive. On the basis of the observations on the worn surfaces by scanning electron microscope and 3D white-light interfering surface profiler, the wear mechanism of the cermet samples was proposed, which includes in extensive plastic deformation, groove, fracture and pullout.

Repeatability Estimation in Galling Resistance Testing

Galling is a severe form of mechanical surface damage, commonly observed in metals, that is accompanied by adhesive transfer, extensive plastic deformation, and/or cold-welding of the mating surfaces. It can lead to seizure or rapid failure of machine components. Stainless steels are particularly prone to galling. A new galling test and analysis method that reflects the statistical nature of galling is described. The new ASTM method (G196), which embodies a probabilistic approach to galling, is superior to an older ASTM test method (G98), which produces only a single threshold stress for a given combination of materials. A computer-modeled experiment involving a 300 series stainless steel is used to illustrate how the enhanced analysis can be applied to determine the repeatability of galling test results.

Plastic Flow and Related Wear Mechanisms of CVD TiC Coatings

Ceramic coatings have been widely used in cutting tools and various machine parts. Even though high strengths have been obtained in most ceramic coatings, it has also been shown that ceramic coatings undergo extensive plastic deformation during scratch and wear tests. Therefore, it is essential to understand the plastic flow and related friction and wear behaviour. Reciprocating multipass wear tests have been carried out on chemical vapor deposition (CVD) TiC coatings. Obvious plastic flow was observed on the rough surface of CVD TiC ceramic coatings in the first sliding, due to the extremely high contact pressure developed on the contact asperities. However, shake down may be quickly reached after several subsequent traverses. In further repeated traverses, the plastic-elastic flow accumulates residual strain energy to the point where cracking, microbuckling, and microflaking may occur along the elastic-plastic interfaces behind the indenter. The new rough surface will appear after the detachment of the heavily strained plate-like wear debris. The repeated sliding allows the process- “plastic flow of asperities - flatten the surface and shake down - microbuckling and detachment of strained layer” to continue until the coating is totally worn out.

Nanoscale Morphology and Indentation of Individual Nacre Tablets from the Gastropod Mollusc Trochus Niloticus

The inner nacreous layer of gastropod mollusc Trochus niloticus is composed of ∼95 wt% planar arrays of polygonal aragonite-based tablets (∼8 μm wide, ∼0.9 μm thick, stacked ∼40 nm apart) and ∼5 wt% biomacromolecules. High-resolution tapping mode atomic force microscope images enabled nanoscale resolution of fractured tablet cross-sections, the organic component, and deformation of individual nanoasperities on top of tablet surfaces. Nanoindentation was performed on individual nacre tablets and the elastic modulus E and yield stress σy were reduced from elastic-plastic finite element simulations yielding E = 92 GPa, σy = 11 GPa (freshly cleaved samples) and E = 79 GPa, σy = 9 GPa (artificial seawater soaked samples). Images of the indents revealed extensive plastic deformation with a clear residual indent and surrounding pileup.