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外文原文
Experimental Evaluation of the Attenuation Effect of a Passive Damper on a Road Vehicle Bumper
Abstract：To mitigate the degree of damage to passengers caused by automobile collisions, a friction damper was built and used in experimental tests to test its effectiveness in impact energy attenuation. The study revealed that energy absorption capacity of a bumper can be improved with the addition of a friction damper. The results revealed that the addition of the friction damper to an automobile bumper to give a bumper-damper system could attenuate about 32.5 % more energy than with the bumper alone. It can be concluded that the effectiveness of automobile bumpers to withstand impact of vehicles by absorbing the kinetic energy from the impact can be improved with the use of a passive friction damper. That is, a passive friction damper system could be used to attenuate more road vehicle impact energy in collisions.
Keywords：Vehicle Bumper, Equivalent Energy Speed (EES), Impact Attenuation, Passive Damper
1. Introduction
Over the past 20 to 30 years, Bumper design concepts have changed drastically. EEA [6] describes four basic bumper design principles (Where necessary, specific features can also be combined). They are: First, the traditional design with a visible metallic transverse beam that decorates the front or rear end of the vehicle and acts as the primary energy absorber during collision； which is seldom used today. Secondly, the plastic fascia and reinforcing beam system that is fixed directly to the front/rear longitudinal beams. This design increases the overall vehicle crashworthiness but leads to a small sacrifice in bumper performance. Thirdly, the system consisting of three components: a plastic fascia, a reinforcing beam and mechanical energy absorbers. The energy absorbers come in two types. They may be either of a reversible type (“shock absorbers”) or deformation elements (“crash boxes”) which are usually replaced after a crash. Lastly, a system, which is more pedestrian friendly in leg impact, which includes a plastic fascia, a reinforcing beam and a propylene foam or a honeycomb energy absorber placed between the plastic fascias and reinforcing beam.
An automobile bumper is the front-most or rear-most part, specially designed to allow the car to sustain low speed impact without damage to the vehicle’s safety systems. That is, they are not capable of reducing injury to vehicle occupants in high speed impacts [7] [8]. It is required to pass an impact test at 4 km/h (2.5 mph) with no
visible damage to the body. Bumpers keep safety-related equipment such as headlights and taillights, hoods, fenders, exhaust and cooling systems, away from damage. Some bumper designs have the provision of cushioning and support of the lower limb； as well as the integration of impact sensors and exterior airbags [9]. The main method proposed for cushioning the lower limb in an impact uses an energy absorber in front of a semi-rigid beam. Energy absorbers proposed include plastic foams (single or multi-density), molded plastic “egg-crates”,“spring-steel”, composite steel-foam, and crush-can energy absorbers [9]. Exposed steel bumpers that involve
frontal airbags design are also alternative design concepts that appear to be adaptable to meet the pedestrian’s safety requirements but these may be costly and require advanced sensors to function efficiently [9].
Bumpers could be designed to absorb more energy than they usually do with some modification of the design and possibly with the use of additional energy absorption devices. This work seeks to apply a passive control system which is an uncontrolled damper that requires no input power to operate. Passive control systems attenuate or absorb vibrations automatically without the need of an electrical control system. They are simple and generally low in cost, but are unable to adapt to changing needs after installation. The passive control system was selected for this work because of its stability, simplicity and low cost in its application. Passive systems include base isolation systems, viscoelastic dampers, bracing systems and friction dampers [12]. Base isolation systems are used to isolate the dynamic force transfer from the structure to the base. Viscoelastic dampers attenuate the force due to external loads using their natural damping properties. Bracing systems are usually made up of brace frames and are usually used to permanently stabilize buildings from external forces such as wind loads and earthquakes by stiffening the structural components； and lastly friction elements consist of dampers that use dry friction to dissipate energy. They are also referred to as Coulomb Damping Systems. Wittman [13] suggested the use of friction to absorb kinetic energy in crash situations by regulating the amount of pressure or normal force on the friction element. The friction element was selected for this study because it does not need external energy, it is robust, and low cost. Even though viscous damping shares most of these advantages, the friction damper’s dryness and therefore no risk of leakages during operation makes it preferable. Although using friction to absorb energy has a big potential, little has been done to exploit it in attenuating crash energy.
Figure 1 shows that, males of age 15 to 44 years are more likely to be involved in road traffic crashes than females. Most breadwinners of families and communities are males in the developing world. Since about 90% of all traffic deaths occur in the developing world, and the majority of these victims are in their most productive years, road crashes are taking a big toll on the livelihood at majority of people on earth [3]. This is a cause for concern that needs to be addressed.
King et al. [14] reported that bumper systems on passenger cars available in North America, though built to meet specific government standards, had different impact characteristics among different vehicles and that certain vehicles could sustain significant front or rear impacts without sustaining damage. There have been efforts to improve on the energy absorption capacity of the bumper. For example, bumper isolators are shock absorbers that are mounted between the vehicle frame and bumper, and are specially designed to reduce an amount of property damage to vehicles [15]. Impact attenuation has been investigated by different people using different methods over several years. Grassie [16] [17] investigated the dynamic load attenuation by rail pads in laboratory and on track. Esveld [18] claims that ballasted railway track had many superior advantages.
By using stiffness of a vehicle and its components, the kinetic energy loss in deformation on vehicles can be estimated. In an investigation, Vangi [19] estimated the stiffness of a vehicle by estimating the geometric parameters of the damage starting from a photograph of generic damage, with documented Equivalent Energy Speed (EES), on a vehicle of the same model as the one under investigation. This method was validated performing crash tests and using data from crash tests found in the literature. The method estimated the kinetic energy loss in deformation on vehicles with sufficient accuracy [19].
Different impact attenuation measures have been used in the railway industry, for example, to mitigate the effect of high forces on the sleeper. In one of such examples, the force content is filtered and attenuated by the softening medium, rail pad installed between sleeper and rail [20]. Similar measures can be introduced in the automobile bumper system to improve its mitigation of high impact forces at higher speeds. Kaewunruen and Remennikov [21], in their test to find the effect of impact loads on railway seats, used a drop hammer and a specially designed fixture to transfer the impact load to the specimens. This study aims at helping to solve part of this serious problem through the development of a more effective crash attenuation system. Hence, the objective of this work is to find out experimentally, whether the addition of a passive damper to a road vehicle bumper could improve its impact energy absorption capability.
Figure 1. Global road traffic fatalities by sex and age (Source: [3]).
2. Material and Method
An experiment was performed using an impact test machine to investigate whether the impact attenuation capacity of a bumper could be enhanced with the addition of a friction damper. A model of friction damper was designed using springs with a definite stiffness. Special fixtures were made to adapt the impact test machine to the test conditions. Fixtures were fastened to the hammer and machine to give a good surface for the impact. The impact fixture was made in the shape of an L, with webs to strengthen the welded joints. This was clamped to the impact machine as shown in the schematic diagram in Figure 2.
During the experiment, the bumper specimen and the bumper-damper combination, where applicable, were arranged together and the hammer of the impact machine allowed swinging freely to impact on it. The hammer of the impact test machine was raised to specific heights and allowed to fall under gravity to hit the bumper specimen in the experimental setup. During the experiments four different heights were used to give four impact forces.
The angle at which the hammer swings from rest and the angle at which it impacts the test specimen were measured and noted. The angle is as indicated in the schematic diagram in Figure 3. The deformation on the bumper specimen after the impact was measured with a veneer caliper and noted.
Figure 2. Impact test machine with impact (R) and hammer (O) fixtures.
Figure 3. Schematic of a simplified pendulum hammer of an impact test machine.
Destructive impact tests were performed on pieces of the bumper specimen. Specimen from two bumpers B and C, from two different cars were used in the analysis. 4 specimens of bumper B and 8 specimens of bumper C were used. The average length of the specimen was 35 cm. The specimen, and where applicable both specimen and damper, were put together, placed on the impact fixture and the hammer allowed to swing freely to impact on it/them.
The friction damper was made with springs of stiffness 44 kN/m. For bumper B, the four bumpers were tested without a friction damper； but for bumper C, four specimens were tested without a damper, and four tested with a damper. The impact forces during the tests were computed and used in the analysis. The results obtained for the two sets of tests are tabulated and presented in Table 1. Bumper B, tested without a damper, was to help establish whether bumper C without a friction element will follow a similar trend. It can be observed that for both bumper samples, results increase steadily with increase in impact load in a linear way. However, the deformation in bumper C is much higher than that of bumper B for the same impact forces. This may be due to the different material properties in the different bumpers. When a friction element was added, in the case of bumper C,the same forces as used in the previous tests, where no friction element was added, could not be used. The now shorter distance of travel of the pendulum to impact on the Bumper-Damper arrangement would not allow the same impact forces to be used. The results show that with increase in impact forces, the deformation starts increasing very slightly at first but at the higher impact force of 9078.95 N it increases drastically from 9 mm (for 7438.27 N) to 27 mm, showing an exponential trend. Curve-fitting method was used to present the curves of the experimental results as described in the next section.
3. Conclusion
A friction damper was built and tested with a bumper to check for its effectiveness to attenuate impact energy. The study showed that energy absorption capacity of a bumper can be improved with the addition of a friction damper. The experimental results revealed that the addition of the friction damper to a bumper to give a bumper damper system could attenuate about 32.5% more energy than with the bumper alone. It can be concluded that the effectiveness of automobile bumpers to withstand impact of vehicles by absorbing the kinetic energy from the impact can be improved with the use of a friction damper.
中文譯文
被動阻尼器對道路車輛保險杠衰減效果的實驗評價
摘要：為了減輕汽車因碰撞引起乘客的傷害程度，從而建立和使用摩擦阻尼器，并進行了實驗測試，以驗證其有效性的能量衰減。這項研究表明，增加保險杠的能量吸收能力，可以提高摩擦阻尼器。結(jié)果表明，添加了摩擦阻尼器的汽車保險杠比沒有添加摩擦阻尼器的保險杠衰減約32.5%以上的能量?？梢缘贸鼋Y(jié)論，汽車保險杠有效抵御車輛的動能，摩擦阻尼器從沖擊中吸取動能。也就是說，一個被動摩擦阻尼器系統(tǒng)可以用來衰減更多道路車輛碰撞能量。
關(guān)鍵詞:汽車保險杠、能量等效速度（EES），影響衰減，被動阻尼器
1．介紹
在過去的20到30年里，保險杠的設(shè)計理念發(fā)生了巨大的變化。EEA [6]描述了四種基本的保險杠設(shè)計原則（在必要的時候，具體的功能也可以結(jié)合）。它們是：首先,傳統(tǒng)的設(shè)計是把車輛的前方或后方的可見金屬橫梁裝飾和車輛碰撞期間作為主要的能量吸收器；這重如今已經(jīng)很少使用了。其次，用塑料筋膜和加強梁直接固定前/后縱向梁。這樣的設(shè)計增加了汽車的整體碰撞性能而保險杠性能則有所衰減的。第三，系統(tǒng)的控制由三部分組成：一個塑料筋膜，加強梁和機械能量吸收器。能量吸收器有兩種類型，他們一個是可逆式（“減震器”）另一個是變形的因素（“碰撞盒”）碰撞盒通常是崩潰后更換的。最后一個系統(tǒng)，是對行人腿部沖擊的一個保護，其中包括一個塑料筋膜，一個加強梁和一個丙烯泡沫或塑料面板和加強梁之間放置的蜂窩能量吸收器。
汽車保險杠是裝在汽車的前后端,用來吸收和緩沖外界沖擊力的汽車安全系統(tǒng)。也就是說，他們能夠減少車輛在高速碰撞時的影響[7] [8]。這是需要通過一個沖擊試驗來證明，在4公里/小時（2.5英里），身體沒有可見的損害。保險杠保持安全的相關(guān)設(shè)備如前大燈和尾燈罩，擋泥板、排氣和冷卻系統(tǒng)。一些保險杠的設(shè)計提供了對緩沖墊的支持，以及傳感器的影響和外部安全氣囊的集成[9]。主要建議用前端的半剛性梁來緩沖下肢的沖擊。能量吸收器包括塑料泡沫（單個或多個密度），模壓塑料蛋箱，“彈簧鋼”，復(fù)合鋼泡沫，破碎能吸能器[9]。暴露的鋼保險杠，包括正面安全氣囊的設(shè)計以及不同的設(shè)計概念的出現(xiàn)都是為了適應(yīng)和滿足行人的安全要求，但這可能是昂貴的，需要先進的傳感器來發(fā)揮有效的功能[9]。
保險杠的設(shè)計可以吸收比他們通常做一些修改的設(shè)計更多的能量并可能使用額外的能量吸收裝置。這項工作旨在應(yīng)用被動控制系統(tǒng)是一種不受控制的阻尼器，不需要輸入功率來操作。被動控制系統(tǒng)對沒有電氣控制系統(tǒng)的需要減弱或吸收振動自動。他們很簡單一般成本較低，但安裝后無法適應(yīng)變化的需要。被動控制系統(tǒng)由于其穩(wěn)定性、簡單性和低成本的應(yīng)用而被選為這項工作。被動系統(tǒng)—包括基礎(chǔ)隔震系統(tǒng)，粘彈性阻尼器，支撐系統(tǒng)和摩擦阻尼器[12]?；A(chǔ)隔震系統(tǒng)是用來隔離從結(jié)構(gòu)的動態(tài)力的基礎(chǔ)。粘彈性阻尼器衰減由于采用自然阻尼性能的外部荷載力。支撐系統(tǒng)通常是由支撐框架，通常用于從外部力量，如風的永久穩(wěn)定建筑物荷載和地震作用下的結(jié)構(gòu)構(gòu)件，最后的摩擦元件組成的阻尼器利用干摩擦耗散能量。他們也被稱為庫侖阻尼系統(tǒng)。威特曼[13]建議使用摩擦吸收動能在碰撞的情況下，通過調(diào)節(jié)壓力的量或摩擦元件的法向力。本研究選擇的摩擦元件，因為它不需要外部能源，它是強大的，低成本。即使粘滯阻尼股份的這些優(yōu)勢，在操作過程中，摩擦阻尼器的干燥，因此無泄漏使它更好。雖然使用摩擦吸收能量有巨大潛力，幾乎沒有衰減的碰撞能量利用。
圖1顯示，年齡在15歲至44歲的男性更容易被卷入道路交通事故而不是女性。家庭最掙錢的人和社區(qū)發(fā)展中世界的男性。由于90%的交通死亡發(fā)生在發(fā)展中國家，大多數(shù)的這些受害者是在他們最具生產(chǎn)力的年，道路交通事故是在大多數(shù)人在地球上的生活造成了巨大的損失[3]。這是一個值得關(guān)注的原因，需要解決。
King et al. [14]報道說，在北美國的客運車輛保險杠系統(tǒng)，雖然建立以滿足特定的政府標準，有不同的影響，在不同的車輛和某些車輛可能會保持顯著正面或后方的影響，而不受損害。有努力提高保險杠的能量吸收能力。例如，保險杠減振器減震器安裝到車架和保險杠之間，是專門用來減少車輛[15]財產(chǎn)損失金額。不同的人使用不同的方法，在過去幾年的影響衰減已被調(diào)查。格雷賽[16][17]研究了動態(tài)載荷的衰減在實驗室和軌道墊。Esveld[18]認為，鐵路有許多優(yōu)點。
通過使用剛度的車輛及其組件，在車輛上的變形的動能損失可以估計。在調(diào)查中，vangi[19]估計車輛的剛度的損傷從遺傳損傷照片的幾何參數(shù)的估計，有能量等效速度（EES），對車輛的同一模型下的一個調(diào)查。這種方法進行了驗證，進行碰撞測試和使用數(shù)據(jù)從碰撞測試中發(fā)現(xiàn)的文獻。該方法估計的動能損失在變形的車輛具有足夠的精度[19]。
不同的沖擊衰減措施已被用于在鐵路行業(yè)，例如，以減輕影響的高力量的臥鋪。在這樣的例子中，力的內(nèi)容被過濾和衰減的軟化介質(zhì)，軌道墊安裝在臥鋪和鐵路之間[20]。kaewunruen和remennikov[21]在汽車保險杠系統(tǒng)中引入了類似的措施，以提高其在較高速度下的高沖擊力。在他們的測試中發(fā)現(xiàn)鐵路座椅沖擊載荷的作用，用錘和一個專門設(shè)計的夾具作為沖擊載荷的標本。本研究旨在幫助解決這一嚴重的問題，通過一個更有效的碰撞衰減系統(tǒng)的發(fā)展的一部分。因此，這項工作的目的是要找出實驗，無論是添加的被動阻尼器的道路車輛保險杠可以提高其沖擊能量吸收能力。
圖1 全球道路交通死亡的性別和年齡（來源：[3]）。
2．材料與方法
使用沖擊試驗機進行了實驗，調(diào)查顯示具有沖擊衰減能力的保險杠可以提高與添加摩擦阻尼器能力。采用彈簧剛度的彈簧設(shè)計的摩擦阻尼器的模型，為適應(yīng)沖擊試驗機對試驗工況的影響。將固定裝置固定在錘和機器上，以使其表面有良好的沖擊。沖擊夾具是用一個升降網(wǎng)來加強焊接接頭。如圖2所示是沖擊機的夾緊原理圖。
在試驗期間，保險杠試樣和保險杠阻尼器的組合，在適用的情況下，被安排在一起，錘的沖擊機器可以自由擺動。沖擊試驗機的錘被提高到特定的高度，并允許在重力作用下撞擊保險杠試樣的實驗裝置。在實驗中，四個不同的高度形成四個沖擊力。
錘子波動的角度從休息的角度影響試樣測量和指出。角度表示的示意圖如圖3所示。后保險杠標本上的變形影響單板卡尺測量,指出。
圖2 沖擊試驗機(R)和錘沖擊機（O）固定裝置
圖3 沖擊試驗機的簡化擺錘示意圖
對保險杠試樣進行了破壞性的沖擊試驗。從兩個不同的汽車進來分析兩個緩沖器B和C的樣本。4個試樣的保險杠乙和8個試樣的保險杠使用。試樣的平均長度為35厘米。試樣，以及適用的標本和阻尼器，放在一起，在沖擊夾具和錘的自由地擺動下，分析對他們的影響。
摩擦阻尼器是彈簧剛度44千牛/米B保險杠，四個保險杠測試沒有摩擦阻尼器；但C保險杠有，四個標本進行測試，沒有一個阻尼器，和四個測試阻尼器。在測試過程中的沖擊力用于分析和計算。兩組試驗獲得的結(jié)果列在表1中。沒有一個阻尼器的保險杠，是有助于建立是否保險杠沒有摩擦元件將遵循類似的趨勢?？梢杂^察到，對于兩個保險杠樣品，結(jié)果穩(wěn)步增加，增加沖擊載荷的線性方式。然而，在保險杠上的變形要遠高于相同的沖擊力的保險杠。這可能是由于不同的保險杠的材料屬性造成的。當有一個摩擦元件添加在保險杠的情況下，賦予以前的測試中使用的相同的力量，與不添加摩擦元件相比，則保險杠不能使用?，F(xiàn)在的短距離的擺錘的沖擊對保險杠安排不允許使用相同的沖擊力。結(jié)果表明，隨著沖擊力的增加，變形開始增加的非常輕微，但在較高的沖擊力（9078.95氮）下，它從9毫米（7438.27氮）急劇增加至27毫米，呈指數(shù)趨勢。曲線擬合的方法是用來呈現(xiàn)在下一節(jié)中所描述的實驗結(jié)果的曲線。
3．結(jié)論
建立了一種摩擦阻尼器，并對其進行了測試，驗證了其有效性對沖擊能量衰減的影響，研究表明：隨著摩擦阻尼器的加入，保險杠吸能的能力得到改善。實驗結(jié)果表明，增加的摩擦阻尼器的保險杠，給予保險杠阻尼器系統(tǒng)比單獨的保險杠衰減約32.5%以上的能量?？梢缘贸鼋Y(jié)論，汽車保險杠摩擦阻尼器的改進能有效承受與吸收沖擊動能對車輛的影響。