How the USSR Studied Leopard 2 Rollers: A Study of Load-Bearing Capacity
It is officially believed that the first German Leopard 2 fell into the hands of domestic researchers quite recently, having been captured almost completely operational in the area of a special military operation in Ukraine. And this is, in general, true: this entire танк had never visited us before. But individual components of its early modifications visited us back in the Soviet Union - in the 1980s.
Moreover, this concerns not only the commander’s panoramic sight-observation device, which has been thoroughly tested on domestic models of military equipment (link to report), but also support rollers. They, as the basis of the design and operational indicators of the chassis of the German machine, were also studied by Soviet researchers in full, comparing them with domestic products in terms of load-bearing capacity.
We offer the results of these studies in full, without cuts, for reading. Of course, they will not answer the question of whether the Leopard 2 is bad, but they show the level of design thought and technology of those years quite well.
Study of the load-bearing capacity of the road wheels of the Leopard 2 tank
The 55-ton West German Leopard 2 tank uses a 7-support chassis with 2-row rubberized road wheels with a diameter of 700 mm with removable disc-shaped aluminum alloy disks. The rollers roll on a track with a metal tread and a staggered overlap of the gaps between the articulated tracks.
One of the characteristic features of the road wheels of the Leopard 2 tank, compared to the rubber road wheels of the domestic T-80 and T-72 tanks, is the use of rubber tires of a smaller height (1,4–1,5 times) and width (1,2–1,3 times) (Fig. 1), which made it possible to reduce the weight and dimensions of the road wheels. Thus, the weight of the disk with a tire for the road wheels of the Leopard 2 tank is 46 kg, which is 20% less than that of domestic tanks.
The desire of the designers of the road wheels of the Leopard 2 tank to reduce the dimensions and, in connection with this, the need to ensure acceptable thermal stress of the tires led to a decrease in the height of the tire mass. This, in turn, led to an increase in mechanical stress in the rubber, the criterion for which is the specific pressure in contact between the tire and the track.
As is known, the bearing capacity of the roller depends on the load on the roller, the specific pressure in contact with the track, thermal stress, mechanical strength and heat resistance of the rubber tires. An important factor is the dynamic loading of the roller, caused by the interaction with the tread. It depends on the shock-absorbing properties of the tires.
The study of the bearing capacity of the support roller of the Leopard 2 tank was carried out by calculation and experiment. The calculation showed that the tire of the support roller of the Leopard 2 experiences approximately the same average static load as domestic tanks Pc = 24,5 kN.
Due to the lack of data on the preliminary track tension T0, the coefficient of uneven distribution of the load on the side k1 and between the tires kп for the Leopard 2 tank, the following values of these indicators were adopted: T0 = 0,1 G, k1 = 1,05 and kп = 1,05 for all rollers (G is the weight of the tank). The calculation, carried out using the dependencies, showed that with smaller dimensions of the rubber mass of the tires of the Leopard 2 road wheels compared to the rollers of domestic tanks, the specific pressure in contact with the track, all other things being equal, turned out to be ~ 1,25 times higher than that of the rollers of the T-80 and T-72 tanks. The results of static tests of these rollers on a press with a conditionally equilibrium state of the rubber mass confirmed a higher level of specific pressure in contact with the track of the Leopard 2 road wheel (Fig. 2).
Thus, with an average static load of 24,5 kN, the specific pressure in contact between the tire of these support rollers and the metal running track of the track reaches 1,8 MPa, while for the T-72 (in contact with the metal running track) and the T-80 (in contact with the rubberized running track of the track) it is 1,5 MPa.
The thermal stress of the Leopard 2 tank support roller tire was estimated based on the maximum steady-state temperature T in the rubber mass of the tire while rolling at a given speed along the track of the caterpillar.
The tire heating temperature was determined under a load of 24,5 kN depending on the duration of the bench tests in the range of typical operational rolling speeds (Fig. 3). Due to the absence of the Leopard-2 tank track, its roller was tested on the track of the domestic T-72 tank, which also has a metal tread like the Leopard-2 track. When testing the tires of the T-80 and T-72 tanks, serial tracks of these tanks were used.
The experiment showed that the temperature at the average, hottest point of the cross-section of the Leopard 2 tank tire is 160-170 °C, which is 25% lower than the heating temperature of the tires of the T-80 and T-72 tanks when rolling on serial tracks at a speed of 70 and 60 km/h, respectively.
When assessing the mechanical fatigue strength of the road wheel tires of the Leopard 2 tank, the influence of the new manufacturing technology and tire material on this indicator was revealed.
If we use the known dependence of the durability of tires by mechanical strength on the value of specific pressure for tires made of domestic serial rubber 34RI-14, then at a higher level of specific pressure (1,8 MPa), due to the reduced dimensions of the Leopard-2 tire array, their durability by mechanical strength of the array compared to domestic tires should be at least 2 times lower. Due to the fact that the rubber composition and manufacturing technology of the Leopard-2 tank tires differ from domestic ones, an experimental assessment of the actual mechanical strength of the Leopard-2 tank roller tire was carried out. Bench tests of the compared tires were carried out at Pc = 24,5 kN and rolling on a tread made of rubberized tracks of the T-80 tank and special metal plates with transverse strips, which have an additional damaging effect.
During the testing of the tires, their heating temperature remained constant. Despite the high level of specific pressures, due to the small dimensions of the rubber mass, the tires of the West German tank have a comparatively high durability: their operating time before failure, obtained under the above conditions taking into account the reduced thermal stress, turned out to be close to the operating time of the domestic tires of the T-80 tank. At the same time, the destruction of the tires of the Leopard-2 tank, unlike the domestic ones, was distributed evenly along their circumference.
The obtained results are determined, first of all, by the more advanced technology of manufacturing the tires of the Leopard-2 tank (by injection molding), and also, apparently, by the higher strength properties of the rubber. The significant influence of these factors was confirmed by the results of mechanical strength tests of an experimental domestic tire, manufactured in the sizes of the tire of the Leopard-2 tank by injection molding from 4E-1386 rubber with increased strength indicators. The service life of such a tire before failure was at the level of the service life of the tire of a West German tank.
The service life of the Leopard 2 tank tires tested at the maximum heating temperature and maximum rolling speed of 70 km/h ("heat resistance") was 3000 km on the metal tread of the T-72 tank track and 7862 km on the rubberized track of the T-80 tank, which is lower than the service life of serial domestic tires at the maximum heating temperature and maximum rolling speed. At the same time, there are a significant number of domestic tires that fail after a short run (300-500 km) both during bench and running tests due to the presence of hidden defects caused by the instability of the tire manufacturing quality. It should be noted that during heat resistance tests, the failure of the Leopard 2 tank tires on the bench is of a fatigue nature, just like during mechanical strength testing, and is also evenly distributed around the tire circumference.
An analysis of the nature of the destruction of the tires of the Leopard 2 tank during bench tests for both mechanical strength and heat resistance shows that it occurs as a result of the development of mechanical damage, evenly distributed over the circumference and thickness of the tire, which indicates the homogeneity of its rubber mass and high quality of manufacture. At the same time, the destruction of the rubber mass of domestic tires is, as a rule, local in nature, determined by the presence of heterogeneities or internal defects in the mass, with subsequent spontaneous development of destruction due to radial runout of the tires.
This type of destruction and the presence of defects are associated with the adopted manufacturing technology of layer-by-layer rolling of calendered rubber tape with subsequent vulcanization in autoclave presses. The casting method used in the manufacture of the tires of the support rollers of the Leopard 2 tank is more progressive. As the study showed, it ensures high homogeneity of the properties of the rubber mass.
Thus, the reduction in the dimensions of domestic tires with a high level of their durability can be achieved through the development of a more progressive tire manufacturing technology that ensures uniform properties of the mass and stable tire quality, and the development of new brands of rubber with high strength indicators and low heat generation.
A study of the dynamic loading of the Leopard 2 tank roller (Fig. 4) showed that a decrease in the width and height of the rubber mass worsens the shock-absorbing properties of the tires, and therefore the level of dynamic loads on the support rollers when interacting with the tread of the tracks increases compared to the rollers of the T-80 tank. Thus, at typical rolling speeds of 25, 35 and 50 km/h, the overloads of these rollers are 1,9, 1,6 and times greater, respectively, than those of the T-80 tank.
It should be taken into account, however, that the actual dynamic overloads on the rollers of the Leopard 2 tank when rolling on the serial tracks of this tank may be less due to the staggered overlap of the gap between the tracks.
Conclusions:
1. The tires of the road wheels of the Leopard 2 tank and domestic tanks bear approximately the same average static load.
2. A distinctive feature of the road wheel tires of the Leopard 2 tank is the small height and width of the rubber mass, which determines a higher level of specific pressure in contact between the tires and the track (1,8 MPa) compared to the road wheels of domestic serial tanks (1,5 MPa) with an acceptable thermal stress of the tires.
3. The road wheels of the Leopard 2 tank have a comparatively high load-bearing capacity due to more advanced technology for the casting of tires and better strength properties of rubber.
Source:
"Study of the bearing capacity of the road wheels of the Leopard 2 tank". V. A. Varchev, Yu. Ya. Istomin, V. I. Korzh, et al.
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