Quasi-static and low-velocity impact mechanical behaviors of entangled porous metallic wire material under different temperatures

Yi-wn Wu ,Hu Cheng ,Shng-zhou Li ,Yu Tng ,Hong-i Bi ,Chun-hong Lu

a Engineering Research Center for Metal Rubber,School of Mechanical Engineering and Automation,Fuzhou University,Fuzhou,350116,China

b Department of Automotive Engineering,Hebei College of Industry and Technology,Shijiazhuang,050091,China

Keywords:Entangled porous metallic wire material Low-velocity impact High temperature Energy dissipation characteristics Mechanical behavior

ABSTRACT To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire materials (EPMWM) for vibration isolation was previously investigated.In this paper,a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented.The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures(25 °C-300 °C) are systematically studied.The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced.During the impact experiments,the impact energy loss rate of EPMWM was between 65% and 85%,while the temperatures increased from 25 °C to 300 °C.Moreover,under the same drop impact conditions,the overall deformation of EPMWM decreases in the temperature range of 100 °C-200 °C.On the other hand,the impact stiffness,energy dissipation,and impact loss factor of EPMWM significantly increase with temperature.This can be attributed to an increase in temperature,which changes the thermal expansion coefficient and contact state of the internal wire helixes.Consequently,the energy dissipation mode (dry friction,air damping,and plastic deformation)of EPMWM is also altered.Therefore,the EPMWM may act as a potential candidate material for superior energy absorption applications.

1.Introduction

Impact loading has emerged as a severe threat to many engineering applications.It requires appropriate materials to enhance energy absorption and improve the viability of structures.Entangled porous metallic wire material (EPMWM) is a type of elastic porous metal material made of various metal wire helixes through a series of special processes [1].EPMWM has excellent structural properties(high porosity,high connectivity of active pores,fibrous behavior,and designability) and non-structural properties (elasticity,repeatable energy absorption,and adaptability to harsh environment).Compared with the polymer materials (such as natural rubber),EPMWM has superior vibration isolation and buffer performance.In addition,it can maintain stable performance under extreme conditions such as corrosion,high pressure,vacuum,irradiation,or high-low temperature alternation.Therefore,the EPMWM has been widely used in ocean exploration equipment[2],planetary exploration landers[3],aero-engine[4],and artillery[5].

EPMWM has also been widely employed in structural design,filtration,sound absorption,sealing,impact resistance,and antipenetration aspects.Rodney et al.[6] proposed EPMWM with reversible dilatancy made of elastic fibers.Mechanical behavior from the elongation of wire helixes and spacing under tensile and compression test effects were caused by the interaction between rearrangement.Compared with other porous materials,such as aluminum honeycomb and metal foam,the EPMWM has outstanding repeated energy absorption characteristics.Furthermore,EPMWM has strong designability.Hu et al.[7] proposed a type of multi-wire EPMWM that could achieve the specified mechanical properties at a low strain level by reasonably controlling the weight percentage of metal wires.Similarly,Zhang et al.[8]designed a multifunctional copper/steel EPMWM.Moreover,the authors tested its electrical sensitivity to compression force through mechanical-electrical coupling tests.Yang et al.[9] proposed a composite filter material with EPMWM as the reinforced structure.The proposed material could still achieve emulsion separation after high impact and wear.Jiang et al.[10]experimentally and analytically analyzed the influence of material structure parameters and incident sound pressure level on nonlinear sound absorption characteristics of EPMWM.Yan et al.[11] analyzed the effect of temperature and elastic modulus factor on seal clearance through thermal expansion tests of EPMWM.Gao et al.[12] conducted an anti-penetration test on EPMWM sandwich composite target.The authors proved that the multiple strike resistance of composite armor was improved.To avoid spacecraft failure of nuts during pyrotechnic separation,Su[13]and Zhao et al.[14]adopted an EPMWM vibration isolator to suppress the impact response caused by piston impact in a separation nut.Li et al.[15]employed an EPMWM component to replace the natural rubber part of a selfpropelled gun latch bar.The test proved that the EPMWM component has better buffering performance than natural rubber.

Due to the great potential of EPMWM in some extreme environments involving high and low temperatures,its structural response over a wide temperature range has to be investigated.To evaluate its mechanical properties,Ding et al.[16] established a constitutive model of the EPMWM in a wide temperature range.Hou et al.[17] proposed a new method of EPMWM dynamic damping characteristics based on hysteretic curve decomposition.Moreover,the authors measured the dynamic loss factor in the temperature range of -70°C-300°C.Ma et al.[18] investigated thermo-physical properties of EPMWM in a high-temperature environment.In addition,the authors theoretically explained the thermal expansion mechanism of EPMWM.Ma et al.[19,20] also designed an intelligent rotor bracket using shape memory alloy and EPMWM components.The results showed that the active control of rotor vibration could be achieved under high temperatures and high amplitude vibration.Zou et al.[21] studied the dynamic mechanical response of EPMWM subjected to relatively high strain amplitudes.However,there are only a few reports on the mechanical behavior and energy dissipation mechanism of EPMWM under impact loading.

Recently,the EPMWM has been studied as an energy absorption material under low-velocity impact.The effects of impact velocity and densities of EPMWM on its energy dissipation characteristics at room temperature were also investigated.Moreover,the mechanism of impact energy absorption was also studied [22,23].

In this paper,a series of quasi-static compression and low-speed impact tests of EPMWM are carried out under different temperatures(25°C-300°C).The combination of mechanical behavior and energy dissipation mechanism can place EPMWM utilization in a wide temperature range and play an essential role in applying EPMWM in the impact protection field.

2.Specimens

The metal wire is the raw material of an EPMWM specimen.Proper selection of material and diameter of metal wire plays a vital role in preparing the EPMWM.A suitable material is selected for the unique function.Thus,the wire material is determined by the working conditions of the EPMWM product (such as temperature,humidity,aggressive media,and load).The chemical composition of the selected materials is shown in Table 1.

Table 1 Chemical compositions (wt%) of the raw wires used.

The EPMWM samples were manufactured by a four-step method [24],which was summarized in Fig.1.

(1) Suitable substrates are selected to meet specific requirements.The primary substrates are stainless steel wire,nickel-titanium alloy,and copper/steel bimetallic materials,whose diameter is generally 0.1-0.3 mm.Then,the substrates are wound by special equipment into a specific diameter of dense wire helixes.Dense wire helixes are stretched to the wire helixes with a fixed pitch (generally 5-15 times the diameter of the substrate).

(2) According to the sample size,winding angle,and blank length,parameters are adjusted on the control panel.Then,the blank winding work is automatically completed by the CNC blank winding equipment.

(3) The blank is taken and lowered into the special mold before.Then,several compression moldings under a specific pressure are exerted.

(4) Metal scraps and dirt on the surface of the wires affect the EPMWM samples' performance.Therefore,they need to be cleaned in an ultrasonic cleaning machine for more than 1 h.Lastly,the specimens are dried.

A series of cylindrical EPMWM components with a diameter of 120 mm,a height of 60 mm,and a relative density ρrof 0.29 were made by the aforementioned preparation process.Specific parameters are listed in Table 2.An EPMWM sample is shown in Fig.2.SEM images in the forming and non-forming direction of EPMWM indicate that the EPMWM has a good consistency.

3.Experimental methods

3.1.Quasi-static test

To study compressive mechanical properties of EPMWM samples in a wide temperature range,a microcomputer-controlled electronic universal testing machine (produced by Jinan Tianchen Testing Machine Manufacturing Co.,Ltd.)was selected to carry out a series of quasi-static loading-unloading tests.The energy dissipation and static loss factors are obtained from the test data.The main parameters of the testing machine are as follows: the maximum compression force is 200 kN,the displacement resolution is 0.001 mm,and the force sensor resolution is 0.05 N.The high-temperature environment test chamber (maximum temperature 800°C,precision ±1°C) matching the testing machine can meet the temperature requirements of EPMWM high-temperature mechanical properties test.

As shown in Fig.3,all samples were compressed in the -z direction,and displacement control mode was adopted.A constant loading rate of 5 mm/min was set,and the samples were unloaded at the same rate.The test flow of quasi-static compression is shown in Fig.3(a).To minimize the uncertainty and the influence of local relaxation in the metal helix [7,25] and reduce the influence of uneven contact between the sample and the press plate,10 N of pre-compression was applied to each sample at room temperature(25°C,RT).The loading-unloading test was repeated for three cycles,and the data of the third test was taken.A high-temperature environment may cause a small amount of plastic deformation of the EPMWM.The pre-compression of the sample is sufficient to eliminate the uncertainty of the test and avoid the introduction of new interference factors.Moreover,to stabilize the contact state of the internal wire helixes of EPMWM,load-unloading was conducted twice according to 30%maximum displacement.Finally,the complete load and unload cycle was only done once.After the temperature in the environment chamber reached each preset test temperature (100°C,200°C,and 300°C),the sample was kept at the preset temperature for 30 min to ensure the uniform temperature distribution in the sample.The deviation of each test temperature was within 5°C.All data were post-processed by Origin software.

Fig.1.Preparation process of EPMWM samples.

Table 2 Parameters of EPMWM components.

Fig.2.EPMWM component and SEM.(a) EPMWM.(b) SEM in the forming direction (× 35).(c) SEM in the non-forming direction (× 35).

The static energy dissipation factor ηsand average stiffness ksare used to describe the energy dissipation characteristics and loadbearing capacity of EPMWM under quasi-static loading-unloading conditions,respectively.These can be derived from experimental data.The average stiffness ksis defined as the ratio between the loading force Fmaxand corresponding deformation Xmax,which characterizes the load-bearing capacity of EPMWM under quasistatic load.Energy dissipation by EPMWM in a single loadingunloading cycle is denoted as ΔW,while W represents the energy applied in a loading process.This energy is converted into heat energy by dry friction between the adjacent wire helixes.The remaining energy is converted into elastic potential energy of EPMWM,as shown in Fig.4.For the material with nonlinear damping,the maximum stored energy in a single loadingunloading cycle is represented as U,where U=W - ΔW/2.The static loss factor ηqscan be expressed as [7]:

Fig.3.Quasi-static compression test system and special fixture.(a) test steps.(b) test system.(c) specimen installation.

3.2.Low-velocity impact test

To investigate the buffering and energy absorption performance of EPMWM,a custom-made low-velocity drop impact test system was on all samples,as shown in Fig.5 and Fig.6.The specimens used in the drop impact test were the same as those used in the quasi-static test.A fixture was designed on the base to bolt the specimens in place.By changing the drop height of the 76 kg hammer,all samples were subjected to a series of impacts.The impact velocity was 2 m/s,5 m/s,and 7 m/s,while the corresponding impact energy was 152 J,950 J,and 1862 J.Then,a series of low-velocity impact tests were carried out at different temperatures Ti(25°C,100°C,200°C,and 300°C).

For the low-velocity impact test with a wide temperature range,only a single impact test was carried out on each component to exclude the influence of plastic deformation and other interference factors of EPMWM specimens.To ensure the repeatability of the test,four EPMWM samples with the same parameters were prepared under each test condition.A high-temperature atmosphere electric furnace (SG-QF1200,Shanghai Shijie Electric Furnace Co.,Ltd.) was used for specimen heating.The highest obtainable furnace temperature was 1200°C.Moreover,a predetermined control program for heating and insulation can be set.

The heating process and low-velocity impact test steps are as follows:(ⅰ)Target temperature(T=Ti+Tj)and heating rate(10°C/min)are set on the control panel of SG-QF1200.Then,the chamber temperature increases from the room temperature to the target temperature T.(ⅱ)After the temperature in the furnace reaches the target temperature T,the EPMWM sample is put into the furnace chamber and is held there for 30 min (ⅲ) When the EPMWM sample is ready for the impact,it was removed from the furnace and installed it on a special fixture for the test.The time required to remove the sample from the furnace and complete installation was approximately 10 s.Due to the heat loss within the transfer time range,after the sample was installed,the specimen's temperature was measured by an infrared radiation thermometer.The temperature loss T1at 100°C is roughly 10°C,the temperature loss T2at 200°C is approximately 20°C,and the temperature loss T3at 300°C is nearly 35°C.

The impact energy loss ED,impact energy loss rate ηD,and impact stiffness kDare used to characterize the dynamic mechanical properties of the EPMWM.

As shown in Figs.5 and 6,the loading force and displacement can be directly collected by the force transducer and displacement transducer.Based on the pulse signal collected by the displacement sensor,the hammer velocity Vican be calculated according to the number of pulses per unit time.Velocity Viis expressed as:

Fig.4.Hysteresis loop under quasi-static compression.

According to the energy conservation principle,the total impact energy E0at the moment when the free-falling hammer hits the EPMWM component can be defined as:

Fig.5.Test steps of low-velocity impact.

Fig.6.Low-velocity impact test system: (a) experimental setup;(b) EPMWM samples fixture.

where m is the total mass of the falling hammer,m=76 kg,g is the acceleration due to gravity,g=9.8 m/s2,h is the height of free fall of the falling hammer before the impact,and V0is the initial impact velocity.

The absorbed energy(ED)by EPMWM during the impact can be expressed as:

where V1is the velocity at which the hammer detaches from the EPMWM specimen during the impact unloading process.

The impact energy loss rate ηDis used to evaluate the energy loss capacity of EPMWM under low-velocity impact load:

The impact energy loss rate ηDcan be obtained by combining Eq.(3),Eq.(4),and Eq.(5).Thus,the impact energy loss rate ηDcan be re-expressed as:

The impact stiffness kDrepresents the bearing capacity of the structure,which can be expressed as:

where Fmaxis the loading force and corresponding deformation Xmax.

4.Results and discussion

4.1.Quasi-static characteristics in the wide temperature range

Quasi-static force-displacement hysteresis loops of the EPMWM in a wide temperature range are shown in Fig.7.During the test,the maximum compression load is 50 kN.Typical deformation characteristics of EPMWM under the compression load include the linear elastic stage,long plastic softening stage,and the hardening stage [25].With an increase in the temperature,the plastic softening stage of the force-displacement hysteresis curve becomes shorter.Then,it enters the exponential hardening stage in advance,and the nonlinear characteristic gradually strengthens.In the temperature range of 25°C-100°C,there is almost no plastic deformation of EPMWM components.However,in the range of 200°C-300°C,because the elastic modulus of the EPMWM substrate (austenitic stainless steel wire,06Cr19Ni10) decreases,the EPMWM produces plastic deformation during the compression process(the unloading curve in Fig.7 does not return to the origin).The energy dissipation ΔW,static average stiffness ks,and static loss factors ηsof EPMWM during quasi-static loading-unloading at different temperatures are shown in Fig.8.

The phenomena observed in the previous section can be explained as follows:

(i) The friction coefficient of the metal wire changes with the ambient temperature.The EPMWM base material is austenitic stainless steel wire(304,06Cr19Ni10).Within the ambient temperature from 25°C to 200°C,the friction coefficient of the metal wire surface increases.When the ambient temperature continues to increase,the surface of the wire is gradually oxidized to form a thick oxide film.As the surface friction coefficient gradually decreases,the friction force decreases with it [24].

Fig.7.The quasi-static force-displacement hysteresis curves of EPMWM at different temperatures.

Fig.8.Quasi-static mechanical properties of EPMWM under different temperature environment.

Fig.9.Proportion of contact states of metal helical coils with compressive load increase [26].

(ii) The proportion of the contact state of the wire helixes changes.The thermal expansion of the stainless steel wire gradually increases with an increase in temperature.Moreover,the internal porosity of the EPMWM decreases.During compression,the proportion of three contact states of the internal wire helixes is modified[26](as shown in Fig.9).The percentage of non-contact continues to decrease,the contact proportion of slip and extrusion as well as the number of contact points of the wire helixes increases,thus leading to increased energy consumption.

(iii) Change of energy consumption mode.The plastic deformation of EPMWM due to a high-temperature environment significantly increases energy consumption.In the temperature range of 25°C-100°C,the energy dissipation mode of EPMWM is the dry friction between the wires.On the other hand,in the temperature range of 100°C-300°C,the energy dissipation mode of EPMWM includes not only the dry friction between the wire helixes but also the plastic deformation of EPMWM.

In conclusion,an increase in temperature from 25°C to 100°C results in a slight fluctuation of energy consumption and loss factor,i.e.,1.5%and 3.7%,respectively.At temperatures lower than 100°C,the thermal expansion of EPMWM is negligible and no apparent oxidation occurs.As the temperature increases from 100°C to 300°C,the aforementioned explanations lead to a significant increase in the restoring force,energy dissipation ΔW,static average stiffness ks,and static loss factors ηswith an increase in the temperature.

4.2.Low-velocity impact behavior in the wide temperature range

4.2.1.Impact response

In a wide temperature range,force-time curves of EPMWM samples with a relative density of 0.29 under different impact velocities are shown in Fig.10.The EPMWM specimens experience three stages at different temperatures including linear deformation,soft deformation,and exponential hardening deformation.The aforementioned is shown in Fig.11.

According to Fig.10(a),for the impact velocity of 2 m/s,a sudden load-drop phenomenon occurs when the impact plate collides with the EPMWM sample.For the other two types of working conditions,due to the restrictions on the sampling rate of the device,this loaddrop phenomenon is not evident.This phenomenon indicates the beginning of the relative sliding among a large number of wire helixes.

The dry friction effect is the primary mode of energy dissipation in EPMWM deformation.Zou et al.[27] proposed that different relative sliding modes exist in EPMWM internal wire helixes under different deformation stages: (a) non-parallel sliding,(b) parallel sliding,as shown in Fig.12.

There is a long soft characteristic zone at the initial stage of impact in Fig.11.Inside the EPMWM,a pair of contact beams exists with a larger angle between the contact wire helixes' pressure direction and the normal direction of the plane.When the lateral contact force is higher than the sliding friction force,a non-parallel sliding occurs at the contact point (Fig.12 (a)).This leads to the weakening of the load-bearing capacity of the wire helixes and the emergence of the plateau area.When the sliding friction progresses to a certain extent,the geometric position of the wire helix and the restrictions of other wire helixes is altered.This causes the wire helixes to recover part of the load-bearing capacity and the jumping phenomenon appears(Fig.10).During the final stages of a lowspeed impact,the plateau area and the jumping phenomenon on the curve are not apparent,thus indicating that they rarely occur in the EPMWM internal non-parallel slide among wire helixes.With an increase in the pressure,the interference between wire helixes intensifies and the constraint force increases.Most wire helixes are in the state of extrusion contact(Fig.9),and the force-displacement curve enters the stage of exponential hardening deformation.

Based on Fig.11,the impact force-displacement hysteresis curves of the EPMWM at different temperatures have the following characteristics:

(1) The maximum load and deformation of EPMWM both increase with an increase in the initial impact velocity.As shown in Fig.13,under the same drop impact conditions,the environmental temperature has a minor influence on the maximum EPMWM load.Its maximum deformation is divided into two platforms with a boundary of 150°C.This observation is consistent with Hou et al.[28].

(2) According to Fig.11,as the ambient temperature increases,the soft characteristic stage of the loading curve becomes shorter,and the nonlinear characteristic becomes stronger.The jumping phenomenon of overall deformation is shown in Fig.13.The mechanism of this phenomenon is relatively complex.The main reason for this complexity is as follows.For the same density,initial impact speed and the constant volume of EPMWM,an increase in the ambient temperature alters the volume of the metal wire.Consequently,the contact state and porosity of the metal wire inside the EPMWM are significantly modified.In other words: (i) The elastic modulus E and shear modulus G of the metal wire decrease as the temperature increases.(ii)The proportion of the three contact states of the internal wire helixes of EPMWM changes with temperature (Fig.8).This is the result of the joint action of (i) and (ii).

(3) As the temperature rises,the “small steps” (Fig.11) of the loading curve in the impact force-displacement hysteresis curve gradually become more and more.This phenomenon is more evident at a lower velocity (V0=2 m/s).

4.2.2.Low-velocity impact energy dissipation characteristics

The impact stiffness kD,absolute energy absorption ED,and impact energy loss rate ηDof EPMWM at different temperatures can be calculated based on Eq.(4),Eq.(6),and Eq.(7),as shown in Fig.14.According to the author's previous research work [22],EPMWM has different energy-dissipating modes at different velocities.At the lower impact velocity (V0=2 m/s),the energydissipating mode is mainly characterized as dry friction between metal wires.With an increase in the temperature,the energydissipating modes of EPMWM become dry friction and plastic deformation.As the impact velocity continues to increase(V0=5 m/s and V0=7 m/s),the EPMWM is filled with air in a nonvacuum environment.Thus,the air damping effect is more significant.Therefore,the energy-dissipating modes are dry friction and air damping.With an increase in the temperature,the energydissipating modes are plastic deformation,dry friction,and air damping,as shown in Table 3.

Fig.10.The force versus time curves of EPMWM for different temperature during experiments.

Fig.11.The low-velocity impact force-displacement hysteresis curves of EPMWM at different temperatures.(a) V=2 m/s (b) V=5 m/s (c) V=7 m/s.

Fig.12.Two relative sliding modes of EPMWM between wire helixes during lowvelocity impact:(a) Non-parallel sliding;(b) Parallel sliding.

For the same drop impact conditions,with an increase in the ambient temperature,the impact stiffness kD,absolute energy absorption ED,and impact energy loss rate ηDof EPMWM are roughly divided into two platforms with the boundary of 150°C (Fig.14).When the temperature is relatively low,the wire helixes inside the.

EPMWM are mainly in the non-contact state,i.e.,the volume fraction of the non-contact state is more significant.When the temperature increases,thermal expansion deformation of wire helixes gradually increases.Moreover,thermal deformation fills the pores between the untouched metal wire helixes,i.e.,the volume fraction of the contact state is more significant[18].Therefore,with an increase in temperature,the proportion of the untouched state of the wire helixes in the EPMWM continues to decrease,while the balance of slip and extrusion contacts increases.Furthermore,the number of wire helixes contacts points increases,which contributes to the impact stiffness kD,absolute energy absorption ED,and impact energy loss rate ηD.

For the initial impact velocities of V0=5 m/s and V0=7 m/s,the air density decreases with ambient temperature from the RT to 100°C,which leads to a decrease of air damping and consequently the impact loss factor of EPMWM.However,a rise in temperature leads to a decrease in the elastic modulus of the EPMWM substrate.The EPMWM produces plastic deformation at the initial impact velocity of V0=7 m/s(Fig.15(a-b)).On the contrary,the EPMWM does not produce plastic deformation at the initial impact velocity V0=5 m/s.Therefore,it can be concluded that the impact loss factor of the former is more significant than that of the latter.From 100°C to 200°C,the softening of the metal wire causes a large amount of plastic deformation of EPMWM (Fig.15(b-c)),thus significantly increasing the impact energy loss rate ηD.From 200°C to 300°C,the contact surface of the metal wire is gradually oxidized to form a smooth and compact oxide film(characterized by a yellow color due to an increase in heat,as shown in Fig.15),which slowly decreases the surface friction coefficient.Thus,the impact energy loss rate ηDof EPMWM fluctuates to a small extent.

In general,with an increase in temperature,the impact stiffness of EPMWM and the loss rate of impact energy both increase.This proves that EPMWM is characterized by good damping energy dissipation in a high-temperature environment.As such,it has a promising application prospect in the impact protection field.

Fig.13.The loss rate of impact energy and impact stiffness at different temperatures.

5.Conclusions

Fig.14.The loss rate of impact energy and impact stiffness at different temperatures.

Table 3 The energy-dissipating modes of EPMWM under different temperatures and impact velocities.

Fig.15.EPMWM specimens after completion of high-temperature test (7 m/s).(a) T=25 °C.(b) T=100 °C.(c) T=200 °C.(d) T=300 °C.

In this paper,energy dissipation characteristics of EPMWM at elevated temperatures under quasi-static and low-velocity impact loads were experimentally studied.Four different temperatures,25°C,100°C,200°C,and 300°C,as well as three different initial impact velocities,2 m/s,5 m/s,and 7 m/s,were considered of the following conclusions are drawn:

(1) For the quasi-static test,in the temperature range from 25°C to 100°C,the temperature has a minor effect on the compression properties of EPMWM.As the temperature increases from 100°C to 300°C,the friction coefficient and contact state of the metal wire helixes inside the EPMWM both change,which leads to a change in the energy consumption mode.Thus,the restoring force,energy dissipation ΔW,static average stiffness ks,and static loss factors ηsincrease significantly with temperature rise.

(2) For the low-velocity impact test,the impact energy loss rate of EPMWM is in the range from 65% to 85% as the temperature increases from 25°C to 300°C.Moreover,under the same drop impact conditions,with an increase in temperature,the overall deformation of EPMWM decreases significantly between 100°C and 200°C.On the other hand,the impact stiffness,energy dissipation and impact loss factor of EPMWM increase significantly.This phenomenon can be attributed to an increase in temperature,which affects the thermal expansion coefficient and contact state of the metal spiral inside the EPMWM.Lastly,energy dissipation modes(dry friction,air damping,and plastic deformation) of EPMWM have also changed.

The combination of mechanical behavior and energy dissipation mechanism can provide an insight into EPMWM in a wide temperature range and play an essential role in applying EPMWM in the impact protection field.However,the test method proposed in this paper cannot provide quantitative analysis.Thus,it will be investigated in detail in future works.

Data availability

The data used to support the findings of this study are available from the corresponding author upon request.

Declaration of competing interest

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.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (grant number 51805086) and the Natural Science Foundation of Fujian Province,China (grant number 2018J01763).