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Nanoindentation hardness plot for all tested materials. The color bar includes the standard deviations from measurements for each material. GCs have two characteristic hardness values probably because each GC is a mixture of two substances. Other materials are named and grouped in the same way as Figure 2. For water ice and tholin at 94 K, their hardness values are predicted by using the nanoindentation hardnessmodulus relationship in Figure 4.
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Extensive equatorial linear dunes exist on Titan, but the origin of the sand, which appears to be organic, is unknown. We used nanoindentation to study the mechanical properties of a few Titan sand candidates, several natural sands on Earth, and common materials used in the Titan Wind Tunnel, to understand the mobility of Titan sand. We measured th...
Contexts in source publication
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... possible candidate for Titan sand is water ice. As Barnes et al., (2008) con- cluded from VIMS data, water ice cannot be ruled out as a component of Titan sand, since the dark organic sand on Titan could be a result of homogeneously organic-coated water ice grains. On the surface of Titan, water ice is in a hexagonal phase, also known as ice Ih. Proctor (1966) reported measurements of the elastic modulus of monocrystalline ice Ih over a broad temperature range from 40 K to 240 K, with the elastic modulus of ice gradually increasing with decreasing temperature. Using the elastic constants mea- sured by Proctor (1966), we can estimate the elastic modulus of water ice at Titan's sur- face temperature (94 K) using the method described by Anderson (1963), which is around 11 GPa, shown in Figure 2. From the linear correlation of elastic modulus and hardness in Figure 4, we can estimate the nanoindentation hardness of water ice under Titan's low temperature to be around 0.5 GPa, shown in Figure 3. We can also estimate the elastic modulus and hardness of water ice near its freezing point (270 K), which are surprising only slightly lower than at 94 K (E∼9 GPa and H∼0.4 GPa), shown in Figure 2 and 3, as well. The fracture toughness of water ice is nearly invariant with changing temperature and is around 0.15 MPa·m 1/2 ( Litwin et al., 2012). Water ice has a lower elastic modu- lus and hardness than tholin, but tholin is more brittle. Thus we cannot interpret which material is a better candidate for Titan sand using only their mechanical ...
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... elastic moduli and nanoindentation hardnesses of all of the materials are shown in Figure 2 and Figure 3. Tholin film has a Young's modulus of 10.4±0.5 GPa and hard- ness of 0.53±0.03 GPa, and tholin particles have similar values. A comparison of the load-displacement curves for tholin and fused silica (modulus 72.3±0.2 GPa, hardness 9.5±0.1 GPa) is shown in Figure 1(b). Tholin has smaller maximum indentation load, smaller stiffness, and larger contact area compared to fused silica, which results in smaller hardness and elastic modulus values. However, amorphous organics/polymers (tholin is an amorphous solid, Quirico et al., 2008) usually have moduli in the range of 10 −3 -10 GPa (Meyers and Chawla, 2009), tholin's elastic modulus is on the high end, indicating its large stiffness among this type of material. This may be caused by cross-linking between molecule chains in tholin similar to network polymers (Dimitrov & Bar-Nun, 2002). The high density of cross-linking makes sliding of molecules difficult, so stretching or break- ing of covalent bonds is necessary to deform ...
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... E 0 is the elastic modulus of the material at 0 K. With an elastic modulus value (E) at a given temperature (T), and with the material's melting temperature (T m ), using Equa- tion 7, we can calculate E 0 and then estimate elastic modulus at other temperatures. For amorphous polymers, the glassy transition temperature (T g ) is a critical temperature in- stead of T m (Courtney, 2000). Below T g , polymers are in the glassy regime, have rela- tively high elastic modulus and hardness and are generally brittle. In this regime, Equa- tion 7 holds true for most polymers, with T g replacing T m . While above T g , the elastic modulus of polymers can decrease by several (3 to 4) orders of magnitude and they be- come rubbery, this is called the rubbery regime. Here all the experiments we performed were under room temperature (∼300 K) while on Titan the surface temperature is much lower (94 K), so we need to translate our experimental results to Titan conditions. Tholin is a stable solid at room temperature and it does not melt up to at least ∼350 K (He & Smith, 2014c). According to the fracture toughness test, tholin is very brittle and is un- likely to be in its rubbery regime. Here we use the critical temperature T g or T m =350 K for tholin in Equation 7. With the measured modulus value at a temperature of ∼300 K, we can estimate the modulus of tholin at 94 K to be around 16 GPa (15.73±0.79 GPa), shown in Figure 2. Using the fitted linear relationship between the elastic modulus and the nanoindentation hardness in Figure 4, the nanoindentation hardness for tholin at 94 K can be estimated to be around 0.8 GPa (0.83±0.06 GPa), and is then plotted in Figure 3. The brittleness of glassy polymers would be higher with decreasing temperature; thus tholin should have an even lower fracture toughness at 94 K, which means it would be even more ...
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... elastic moduli and nanoindentation hardnesses of all of the materials are shown in Figure 2 and Figure 3. Tholin film has a Young's modulus of 10.4±0.5 GPa and hard- ness of 0.53±0.03 ...
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... the measured modulus value at a temperature of ∼300 K, we can estimate the modulus of tholin at 94 K to be around 16 GPa (15.73±0.79 GPa), shown in Figure 2. Using the fitted linear relationship between the elastic modulus and the nanoindentation hardness in Figure 4, the nanoindentation hardness for tholin at 94 K can be estimated to be around 0.8 GPa (0.83±0.06 GPa), and is then plotted in Figure 3. The brittleness of glassy polymers would be higher with decreasing temperature; thus tholin should have an even lower fracture toughness at 94 K, which means it would be even more brittle. ...
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... (1966) reported measurements of the elastic modulus of monocrystalline ice Ih over a broad temperature range from 40 K to 240 K, with the elastic modulus of ice gradually increasing with decreasing temperature. Using the elastic constants mea- sured by Proctor (1966), we can estimate the elastic modulus of water ice at Titan's sur- face temperature (94 K) using the method described by Anderson (1963), which is around 11 GPa, shown in Figure 2. From the linear correlation of elastic modulus and hardness in Figure 4, we can estimate the nanoindentation hardness of water ice under Titan's low temperature to be around 0.5 GPa, shown in Figure 3. We can also estimate the elastic modulus and hardness of water ice near its freezing point (270 K), which are surprising only slightly lower than at 94 K (E∼9 GPa and H∼0.4 GPa), shown in Figure 2 and 3, as well. ...
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... possible candidate for Titan sand is water ice. As Barnes et al., (2008) con- cluded from VIMS data, water ice cannot be ruled out as a component of Titan sand, since the dark organic sand on Titan could be a result of homogeneously organic-coated water ice grains. On the surface of Titan, water ice is in a hexagonal phase, also known as ice Ih. Proctor (1966) reported measurements of the elastic modulus of monocrystalline ice Ih over a broad temperature range from 40 K to 240 K, with the elastic modulus of ice gradually increasing with decreasing temperature. Using the elastic constants measured by Proctor (1966), we can estimate the elastic modulus of water ice at Titan's surface temperature (94 K) using the method described by Anderson (1963), which is around 11 GPa, shown in Fig- ure 2. From the linear correlation of elastic modulus and hardness in Figure 4, we can esti- mate the nanoindentation hardness of water ice under Titan's low temperature to be around 0.5 GPa, shown in Figure 3. We can also estimate the elastic modulus and hardness of wa- ter ice near its freezing point (270 K), which are surprising only slightly lower than at 94 K (E∼9 GPa and H∼0.4 GPa), shown in Figure 2 and 3, as well. The fracture toughness of wa- ter ice is nearly invariant with changing temperature and is around 0.15 MPa·m 1/2 ( Litwin et al., 2012). Water ice has a lower elastic modulus and hardness than tholin, but tholin is more brittle. Thus we cannot interpret which material is a better candidate for Titan sand using only their mechanical ...
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... elastic moduli and nanoindentation hardnesses of all of the materials are shown in Figure 2 and Figure 3. Tholin film has a Young's modulus of 10.4±0.5 GPa and hard- ness of 0.53±0.03 GPa, and tholin particles have similar values. A comparison of the load- displacement curves for tholin and fused silica (modulus 72.3±0.2 GPa, hardness 9.5±0.1 GPa) is shown in Figure 1(b). Tholin has smaller maximum indentation load, smaller stiff- ness, and larger contact area compared to fused silica, which results in smaller hardness and elastic modulus values. However, amorphous organics/polymers (tholin is an amor- phous solid, Quirico et al., 2008) usually have moduli in the range of 10 −3 -10 GPa (Mey- ers and Chawla, 2009), tholin's elastic modulus is on the high end, indicating its large stiff- ness among this type of material. This may be caused by cross-linking between molecule chains in tholin similar to network polymers (Dimitrov & Bar-Nun, 2002). The high density of cross-linking makes sliding of molecules difficult, so stretching or breaking of covalent bonds is necessary to deform ...
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... modulus and hardness and are generally brittle. In this regime, Equation 7 holds true for most polymers, with T g replacing T m . While above T g , the elastic modulus of polymers can decrease by several (3 to 4) orders of magnitude and they become rubbery, this is called the rubbery regime. Here all the experiments we performed were under room temperature (∼300 K) while on Titan the surface temperature is much lower (94 K), so we need to translate our experimental results to Titan conditions. Tholin is a stable solid at room temperature and it does not melt up to at least ∼350 K ( He & Smith, 2014c). According to the fracture tough- ness test, tholin is very brittle and is unlikely to be in its rubbery regime. Here we use the critical temperature T g or T m =350 K for tholin in Equation 7. With the measured modu- lus value at a temperature of ∼300 K, we can estimate the modulus of tholin at 94 K to be around 16 GPa (15.73±0.79 GPa), shown in Figure 2. Using the fitted linear relationship be- tween the elastic modulus and the nanoindentation hardness in Figure 4, the nanoindentation hardness for tholin at 94 K can be estimated to be around 0.8 GPa (0.83±0.06 GPa), and is then plotted in Figure 3. The brittleness of glassy polymers would be higher with decreasing temperature; thus tholin should have an even lower fracture toughness at 94 K, which means it would be even more brittle. ...
