This study used low-speed impact and quasi-static compression loadings to see how a microcellular closed-cell aluminum composite foam from the 3000 series aluminum alloy responded. The parent material is the 3000 series aluminum alloy, which has moderate strength, good corrosion resistance, and good formability. In microcellular foams, most cavities are so small that they are considered microcavities. The relationship between density and foam's static and impact behaviors is examined for this type of aluminum alloy. The low-velocity impact tests involved three different falling heights, and the acceleration was recorded in the impact duration before the velocity and absorbed energy calculations. The outcomes reveal that all specimens' stress-strain curve area is sufficiently large to withstand high energy before failure. In this study's case of aluminum foam, the strain rate effect is very pronounced, and the amount of yield and plateau stress under low-velocity impact loading is more significant than quasi-static. Based on dynamic stress-strain results, these microcellular closed-cell aluminum foams exhibit excellent properties, making them a conventional material with a few unique characteristics.
Research Article
An investigation into the quasi-static and low-velocity impact behaviors of 3000 series aluminum alloy microcellular composite foam
https://doi.org/10.21203/rs.3.rs-1949868/v1
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closed-cell foam
microcellular aluminum foam
drop impact loading
foam energy absorption
high-strength foam
Due to its lightweight, high specific strength, and high energy absorption capacity, metal foams have been used in some engineering applications. Researchers are interested in studying the mechanical properties of this material because it is used in so many industrial applications [1, 2].
Aluminum foam, which belongs to the category of metal foam, is extremely strong even though it is still lightweight. It can absorb a significant amount of mechanical energy when deformed, making it a desirable material for use in impact energy absorbers. The aluminum foams have a high surface-to-volume ratio and are exceptionally lightweight despite their extreme durability.
Recyclability, heat and corrosion resistance, strength, and electrical and thermal conductivity are all features that aluminum foam shares with its parent metal while being much lighter in weight. The high specific stiffness of aluminum foam, especially when compared to the base metal, allows it to resist significant deformation.
Open-cell and closed-cell aluminum foams are two different types of aluminum foam. Open-cell foam has small, incompletely closed cavities. Unlike open-cell foam, the cells in closed-cell foam are entirely closed. To better withstand impact loads in engineering applications, closed-cell foam is preferred over open-cell foam. Metal foams under dynamic impact have recently attracted much attention because of their complex yield/failure behavior [3–7].
Closed-cell aluminum foams were studied by M.A. Kader et al. [3] for strain-rate dependency and impact dynamics. Experiments and FEM simulations investigated the low-velocity impact behavior of closed-cell aluminum foams under drop-weight impact and the significant stress increase with increasing strain rates. It was found that the foams' maximum yield stress in the quasi-static test was approximately 5 MPa and that it was around 9 MPa in the impact test. According to the literature [7–10], these results are widely available.
The yield point of foams has been raised in some studies, and they have also been found to have a higher energy absorption behavior under quasi-static and impact loadings [11–14]. Rabiei [11] studied closed-cell metal foam compression behavior. As the authors have stated, the composite metal foam developed in ref [11] had a higher compression strength than other foams made with aluminum and steel as the parent materials. Research showed that, as the density of aluminum foam increases, the yield stress increases, but the amount of stretching that can be done goes down.
This study tested foam with high compressive strength through quasi-static compression and low-velocity impact. The compressive strength (yield stress) and energy absorption of this foam are significantly higher than those of other microcellular closed-cell aluminum foams studied in the literature. The density of the foam is 60% of the base alloy (3000 series aluminum alloy). These aluminum alloys have moderate strength, good corrosion resistance, good formability, and can withstand high temperatures. 3000 series aluminum alloy is used in vehicle and power plant heat exchangers, and moderate strength precludes structural. This study examined how the density of a microcellular closed-cell aluminum foam (3000 series aluminum alloy) affected how much energy it absorbed and how stiff it was.
There is a wide range of uses for glass microspheres, including research, medicine, consumer goods, and various other industries. Microspheres made of glass can range from 10 nanometers to 5 millimeters, but most are between 1 and 1000 micrometers. Syntactic foam, for example, uses hollow spheres as a lightweight filler. As a result, the micro balloons that make up syntactic foam are highly light, have low thermal conductivity, and are incredibly resistant to compressive stress. It is possible to make lightweight aluminum composite foam using a ceramic balloon [15] and other hollow spheres of different materials.
This study's images of the SiO2 micro balloons in the closed-cell aluminum composite foam with an SEM and a light microscope are shown in Figures 1, 2, and 3. The sizes and geometric shapes of the SiO2 micro balloons used in microcellular foams can be seen using these images.
The specimens used in this study were microcellular closed-cell aluminum composite foam specimens made from 3000 series aluminum alloy parental material and ceramic micro-hollow spheres as cavities (Figure 3).
For testing, cubic specimens with densities ranging from 1500 to 1740 kg/m3 (or 60% of pure aluminum's alloy density) were subjected to quasi-static and drop impact loading. A uniaxial compression test is a standard gauge of foam's mechanical properties. Quasi-static compression data can be used to determine the foam yield point and Young's modulus, among other properties.
An accurate load cell (class 0.5) with a capacity of 25000kgf was used to perform quasi-static compression tests on the SANTAM STM-250 servo electromechanical UTM machine, which had constant speed control from 0.01 to 300mm/min. A quasi-static compressive load was applied to four samples at one millimeter per minute. Figure 4 depicts the specimens and testing gear.
A data acquisition system with a data recording speed of 250 kHz was used in the four-meter drop test (Figure 5), which recorded acceleration from an accelerometer mounted on the impactor. The accelerometer on the device can measure between 100 and 500000 m/s2. The accelerometer sensor is placed near the impactor tip to create acceleration-time diagrams. When a weight falls from a certain height, the sample deforms and uses up the kinetic energy. The metal foam absorbs the friction of this energy and continues to deform the sample. For this study, when conducting a test, all specimens were placed on the support without any constraints. The tests were conducted at room temperature, with a constant 35 kg impactor mass, and with the sample resting on a steel plate. Drop heights of 1.5, 2.25, and 3 meters were used in the experiments.
Energy-absorbing structures and materials protect people, vehicles, and buildings from shock and collisions. An impact energy absorber is a material or structure with high plateau stress and a sizeable area under the stress-strain curve. Stress-strain diagrams for these materials are typically long and smooth (Fig. 6). In the "ideal energy absorption zone," which is depicted in Fig. 6, they absorb a large amount of energy during the plateau stress zone.
In this investigation, thirteen specimens were tested; four samples for quasi-static compression, and nine samples to low velocity impact loads. Table 1 lists the details of these specimens.
Under a quasi-static compression load of 1 mm/min, stress-strain curves for specimens SS2, SS3, SS12, and SS13 are shown in Fig. 6.
|
specimen |
SS2 |
SS3 |
SS12 |
SS13 |
TS1 |
TS2 |
TS5 |
TS8 |
TS11 |
TS12 |
TS13 |
TS17 |
TS18 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Density (kg/m3) |
1608 |
1600 |
1653 |
17.31 |
1762 |
1718 |
1691 |
1707 |
1716 |
1700 |
1665 |
1642 |
1679 |
|
Mass (gr) |
16.8 |
16.4 |
18.3 |
18.8 |
15.5 |
15.5 |
14.7 |
15.1 |
14.5 |
14.7 |
21.1 |
22.1 |
20.8 |
|
Area (mm2) |
450.50 |
473.93 |
450.29 |
445.84 |
416.78 |
420.25 |
422.51 |
427.25 |
418.61 |
428.50 |
433.06 |
567.87 |
612.81 |
|
Height (mm) |
21.6 |
21.62 |
24.57 |
24.28 |
21.1 |
21.47 |
20.56 |
20.69 |
20.37 |
20.17 |
20.6 |
23.7 |
20.21 |
It can be seen in Fig. 6 that these materials have a high energy absorption capacity due to their large area under the stress-strain curve. This aluminum foam's yield stress is higher than other commercial aluminum foams, as shown by the stress-strain diagrams.
Figure 6 clearly shows that the diagram is divided into three main sections. During quasi-static loads, the first section of the stress-strain curve is linear elastic, which occurs in the case of small strains, usually less than 5% strain. Consequently, the behavior in this section has a slope equal to the Young module of foam. This foam begins to compress at a specific time but not under constant stress. One can see a work hardening zone that reaches about 50% of the strain range. Elastic buckle, plastic deformation, or brittle crushing of the cell walls causes foam cells to collapse as they are put under more stress. A significant increase in stress from densification causes the cell walls to meet and touch. There is a sharp increase in stress in the densification section, which can be seen in the third section of Fig. 6.
Table 2 compares the foam studied in this study to other foams studied in Refs [11, 14, 16–19]. The Stainless Steel PM Foam studied in Ref [11] has a high strength-to-density ratio of 46.9 with a density of 2.9 g/cm3. The foam investigated in this study has a density of 1.6 g/cm3, which is up to 45 percent lower than the density of Stainless-Steel PM Foam.
Under quasi-static compressional loading, the mechanical properties of specimen SS13 are shown in Fig. 7. There is a calculated Young module for the specimen, which is 840 MPa in the elastic region of the diagram. The Yield stress in this area is around 38 MPa, which is more than most of the other metal foam researched in the literature.
Table 2
strength to the ratio of foams studied in the present study and Refs [11, 14, 16-19]
The average plateau stress is calculated by calculating the area under the stress-strain curve from strain 0.1 to strain 0.5 (this section depicts an ideal energy absorber). Therefore, the equivalent classic behavior of the foam has a plateau stress of \(84.10 \text{M}\text{p}\text{a}\) with a density of 1.6, which is higher than the more significant part of other metal foam studied in the literature.
Three different heights are used to test dynamic impact loads on the nine specimens that were previously mentioned.
Impact drop tests were performed on the test specimens TS1, TS8, and TS13 at an impact drop height of 1.5 m, TS2, TS11, and TS17 at an impact drop height of 2.25 m, TS5, TS12, and TS18 at an impact drop height of 3 m. Figure 8 through Fig. 10 show the impact results, including acceleration, velocity, absorb energy, and stress-strain responses.
Figures 8, 9, and 10 show that impact acceleration and absorb energy are proportional to impactor height; as the height increases, so does the acceleration.
As is illustrated in Fig. 8-(c), Fig. 9-(c), and Fig. 10-(c) the initial energy had the value of 500 Jules for TS1, TS8, and TS13. In contrast, this value for samples TS2, TS11, and TS17 was about 750 Jules, and it had the value of 1050 Jules for specimens TS5, TS12, and TS18. As shown in the figures, increasing the height of the impactor increases both the initial energy and the impact velocity; this increases the slope of the diagram, a shorter time for graphs to reach zero, and a faster rate of compression. For instance, the energy and velocity of a hammer falling from 1.5 m reach zero in approximately 0.003 to 0.0035 seconds, for 2.25 m dropping this time is about 0.003, and for 3 m falling this time is about 0.0025 to 0.003 seconds.
The dynamic stress-strain responses are also interesting since it represents classic foam behavior, as it is depicted in Fig. 8-(d), Fig. 9-(d), and Fig. 10-(d). The most similarity between the dynamic stress-strain responses and the classic foam behavior is observed in Fig. 8-(d), where the yield stress is 200–250 MPa, and the plateau stress is about 150–180 MPa continues in the strains of range 0.1 to 0.4. The results of dynamic stress-strain diagrams are the best way to demonstrate how unique the foam is. These diagrams show how this type of foam behaves similarly to a classic foam. It is clear that this foam is also sensitive to strain rate and that as strain rate increases, so does the amount of energy it can absorb. Also, remember that foam has a higher rate sensitivity than aluminum.
Figure 11 compares the stress-strain diagrams for the quasi-static compression test of four specimens (SS2-SS3-SS12-SS13) and the dynamic drop impact test of samples (TS5-TS12-TS18) from a height of 3 meters. Initially, it is evident that the behavior of the foam in a quasi-static compression test is elastic; however, as the load increases, the foam enters the plastic region and hardens. Eventually, the specimen buckles and collapses, resulting in a sharp rise in stress. In contrast, in dynamic drop impact tests, the impact load is so high that the foam stress-strain diagram is elastic for only minor strain ranges (0-0.05). After that, it begins a plastic region with hardening behavior until a peak with a value of about 250–300 MPa; it has a small drop due to the mass's minor separation. At that point, the plateau stress begins with hardening behavior until the specimen collapses.
Figure 12 compares stress-strain curves of refs [7, 14, 20–22] and two specimens, TS18 and TS12. The diagrams in this study have the highest stress values and the most significant area under the stress-strain curve, resulting in the highest energy absorption value. Aluminum foam dynamic and static behavior, as well as aluminum-steel foam values, are compared here. According to this diagram, the investigated foam has the highest or one of the highest energy absorption values among metal foams.
The 3000 series aluminum alloy microcellular foam is examined in this study for its drop-weight impact and quasi-static behavior. The yield strength of this aluminum foam is one of the highest compared to other aluminum foams studied in the literature. For instance, Stainless Steel PM Foam in Ref [11] has a strength-to-density ratio of 46.9 and a density of 2.9 g/cm3. However, the foam used in this study is up to 45% less dense than Stainless Steel PM Foam, with a strength-to-density ratio of 40 and a density of 1.6 g/cm3. In the quasi-static test, the foam yield strength was 38 MPa, and in the dynamic drop test, it was 250–350 Mpa, and in terms of Young's modulus, the foam measured about 840 MPa. So they could absorb more energy before collapsing due to the large area of the stress-strain curve. A dynamic drop impact test was performed on the specimens to measure acceleration, speed, energy, and dynamic stress-strain relationships. For most aluminum foams under quasi-static and dynamic loading, the effect of strain rate on their behavior is negligible, according to scientific sources. In the case of aluminum foam examined in this study, the strain rate effect is very pronounced. The yield and plateau stress under low-velocity impact loading are more significant than seven times that of quasi-static.
Funding provide
The authors declare that no funding was received for this work.
Conflict of Interest statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. There has been no significant financial support for this work that could have influenced its outcome.
Author's Contribution
M. Jaffari and M. R. Kalhori created the samples and experimented. M. Jaffari wrote the original draft. M. Yazdani; directed the project, conceived the original idea, sample fabrication, designed and performed the tests, signal processing, and data extraction, and edited the final manuscript.
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No competing interests reported.