. A . .. 9. u .7 . .. 0 $9953)? 3w ", n. -. v a . ”sht- h , gr.- '1. ..~. A... _..n ' . . ‘- .4.0',J‘ r 39.1 in: . .r‘u 5.3.!) h . I“I‘w-‘_I“‘.PD”II‘ s Q! q . .‘.. .""c I ‘3? d - .2). 4 ~ ‘7 _r. U “3%;A . .' J - (av-~56 f _ v- L w ,\ 4‘0; 1“" a }. ., ,_ 'fifiuflkw V a ‘2. Ag“ ' .K ”“2 33. . . . Jam,- ~ v: *3‘ 0 g \ ‘nt‘ .4; :3. J. . 77‘3" ' 't‘lt‘r. 0-. w u A“? k“ .- #8 \{E‘{ ‘ :8? .u. 3‘2 u:- . «612$. 31 l mmmm 3 ‘- c; =1; \5 795M “m1... ll‘lllllll: \l‘ \l‘l\‘Tllfjlllllll H WNW 3 1293 This is to certify that the thesis entitled A Comparison of Vertical Vibration Levels For Leaf Spring Versus Air Ride Trailer Suspensions presented by Charles David Pierce has been accepted towards fulfillment of the requirements for _Mas.t.e.r_s_ degree in Eackagjng._ [my Major professor Date_EehznarLZZ.._l_9.9_Q 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution PLACE IN RETURN BOX to remove thle checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE . DATE DUE MAY 0 6199? . —n+ l m“; fifm‘ 0 1 p 93-219 | MSU Is An Affirmative Action/Equal Opportunity Institution A Comparison of Vertical Vibration Levels For Leaf Spring Versus Air Ride Trailer Suspensions BY Charles David Pierce A Thesis Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Master Of Science School of Packaging 1990 $042350: Abstract A Comparison of Vertical Vibration Levels For Leaf Spring Versus Air Ride Trailer Suspensions BY Charles David Pierce Packaging engineers need to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three seperate suspension systems; conventional air-ride, damaged air-ride, and conventional leaf-spring Six tractor trailer shipments with different ladings were monitored over the same shipping route. Power Density plots were developed for various road conditions and suspension type. These in turn were used to compare the vibration levels present at various frequencies. Conclusions from this study are that air-ride suspension when maintained gives lower Power Density (P.D.) levels on all road surfaces. A damaged air-ride suspension and leaf spring suspension are very similar in response frequencies. The damaged air—ride gives higher P.D.1evels at low frequency. Copyright by Charles David Pierce 1990 Acknowledgements I would like to express my sincere appreciation to my major professor Dr. S. Paul Singh for his guidance and everlasting friendship. I also would like to thank the other members of my committee, Dr. Gary J. Burgess, Dr. Julian J. Lee, and Dr. George E . Mase . I also thank Unisys for the support they provided during this study, Wendy Aquilina for providing all her help and Jorge Marcondes and John Antle for all the help they gave me in the past year. Finally, I would like to thank all the faculty and students at the School of Packaging and Michigan State University who have helped to keep me sane over the last year. iv TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . LIST OF FIGURES . . . . . . . . . . . 1.0 INTRODUCTION . . . . . . . . . . 2.0 LITERATURE REVIEW 3.0 EXPERIMENTAL DESIGN 4.0 DATA AND RESULTS . . . . . . . . 5.0 CONCLUSIONS AND RECOMMENDATIONS APPENDICIES. . . . . . . . . . . . . . LIST OF REFERENCES . . . . . . . . . . Page vi 13 27 61 63 76 Table 1. Accelerometer Information . LIST OF TABLES 2. Experimental Design . . 3. Summary of responses for 5000 lb. lading . 4. Summary of responses for 18,000 lb. 1 P.D. -2 P.D. -3 P.D. B B B B-4 P.D. B-5 P.D. B 6 P.D. B-7 P.D. B-8 P.D. B-9 P.D. B-lO P.D. Values Values Values Values Values Values Values Values Values Values for Section 3, 5000 lb. Section Section Section Section Section Section Section Section Section 6, 8, 9, 10, 3, 18,000 lb. lading 6, 18,000 lb. lading 8, 18,000 lb. lading 9, 18,000 lb. lading 10, 18,000 lb. lading vi 5000 lb. 5000 lb. 5000 lb. 5000 lb. lading lading lading lading lading lading . Exp 24 26 38 39 66 67 68 69 70 71 72 73 74 75 LIST OF FIGURES Figure 1. A Typical Air-Ride Suspension . . . . . . . . . . 2. A Typical Leaf Spring Suspensions . . . . . . . . 3. Location of Instrumentation . . . . . . . . . . 4. Setup of Data Acquisition System . . . . . . . . 5. Vertical Rear Trailer Vibration: Background Noise for Analyzing Equipment . . . . . . . . . . 6. Vertical Rear Trailer Vibration: Engine Noise for Stationary Truck . . . . . . . . . . . . . . . . 7. Vertical Rear Trailer Vibration for Asphalt With Severe Cracks, 30 mph (Section 3); Load: 5000 lbs 8. Vertical Rear Trailer Vibration for Asphalt With Joints, Concrete With Joints, 45-55 mph (Section 6); Load: 5000 lbs. . . . . . . . . . . . . . . 9. Vertical Rear Trailer Vibration for Asphalt With Cracks, Smooth Asphalt, 55 mph (Section 8); Load 5000 lbs. . . . . . . . . . . . . 10. Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 9); Load: 5000 lbs. . . . 11. Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 10); Load: 5000 lbs . 12. Vertical Rear Trailer Vibration for Asphalt With Severe Cracks, 30 mph (Section 3); Load: 18, 000 lbs. . . . . . . . . . . . 13. Vertical Rear Trailer Vibration for Asphalt With Joints, Concrete With Joints, 45-55 mph (Section 6); Load: 18,000 lbs. . . . . . . . . . . . . . 14. Vertical Rear Trailer Vibration for Asphalt With Cracks, Smooth Asphalt, 55 mph (Section 8).; Load: 18, 000 lbs. . . . . . . . . . . . . . . . . e Page 21 22 23 25 40 41 42 43 44 45 46 47 48 49 15. 16. 17. 18. 19. 20 21 22 23 24 25 Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 9); Load: 18,000 lbs. Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 10); Load: 18,000 lbs. Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 10); Conventional Air- Ride Suspension. . . . . . . . . . . . . . . Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 10 ); Damaged Air-Ride Suspension. . . . . . . . . . . . . . . . Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 10); Conventional Leaf— Spring Suspension. . . . . . . . . . . . Acceleration Ratio versus Frequency for Road Section 3,5000 lb. Load. . . . . . . . Acceleration Ratio versus Frequency for Road Section 6, 5000 lb. Load. . . . . . . . . . . Acceleration Ratio versus Frequency for Road Section 10, 5000 lb. Load. . . . . . . . . . Acceleration Ratio versus Frequency for Road Section 3, 18,000 lb. Load. . . . . . . . . . Acceleration Ratio versus Frequency for Road Section 6, 18, 000 lb. Load. . . . . . . Acceleration Ratio versus Frequency for Road Section 10, 18,000 lb. Load. . . . . . . . viii 50 51 52 53 54 55 56 57 58 59 60 1.0 Introduction To effectively design a package/product system, it is critical to know the product fragility and expected forces in the distribution environment. Product damage can frequently be traced to various vibration forces that originate in various transport systems. It is important to measure the levels and types of forces present in a company's specific distribution environment. Engineers can use this information in conjunction with the fragility of a product to effectively develop a package system which will protect the product from damage. This information can also be used to evaluate packages in simulated lab shipment tests. Shipment by truck is the most common method, in the United States, for transporting goods over land. Within thirty years, the percentage of freight shipped by truck has increased from 26 percent in 1950 to 37 percent in 1980 (National Council of Physical Distribution Management, 1982). The origin of shock and vibration comes from two sources in a truck/trailer system. 1) External sources, such as road or surface irregularities, braking, and forward acceleration. 2) Internal sources due'to the vehicle itself such as engine vibration, drive mechanisms, and wheel imbalance (Harris, 1961). The magnitude of these shocks and vibrations transmitted to the product are in turn affected by the type of suspension system which supports the truck/trailer system. It is commonly thought that an air-ride suspension will give a much smoother ride than leaf spring, therefore protecting products more efficiently. However, air ride suspensions are much more expensive, estimated to cost an average of $0.30 more per mile (Kelly, 1989). These systems also are known to "break down" frequently, which could result in severe vibration levels. The added cost of an air ride suspension system needs to be justified by a product's need for a lower vibration level and also must be shown to function better than that of leaf spring for given distribution routes. OBJECTIVES The purpose of this study was to measure current vertical vibration levels present in commercial truck-trailer systems for each of the three suspension systems; 1) Conventional air—ride (maintained properly) 2) Damaged air-ride (air bled out of the system) 3) Conventional leaf spring. These levels were measured as a function of lading weight and road surface quality. Specifically, the objectives were to: 1) Quantify the levels of vertical vibration levels for the above three suspension systems over various road surfaces and two different trailer lading weights. 3) Compare the vertical vibration levels measured for each truck-trailer suspension over the same road smite and lading weight. 4) Establish the advantages and disadvantages of air-ride suspension versus a leaf—spring suspension. 2.0 Literature Review Recent environmental studies that have evaluated shock and vibration levels in a truck distribution environment have dealt mainly with leaf spring suspensions. A literature review reveals no prior study, explaining the vibration levels of an air-ride suspension which has been damaged or poorly maintained. Most of these studies present results in the form of RMS acceleration level, or Power Density (P.D.) values versus Frequency. These concepts are explained in more detail in Appendix A. The literature review that follows will be presented in a chronological order to highlight the development which has taken place on this subject. Harris and Crede (1961) presented basic definitions and concepts for shock and vibration concerning road and rail vehicles. They also presented tables of typical shock and vibration levels present in train, truck, and tractor-trailer combinations under normal operating conditions. The Environment Experienced by Cargo on a Flatbed Tractor- Trailer Combination (Foley, 1966) was performed to gather and analyze data for heavy load shipments. Tests were performed on an unloaded trailer and one with a 15 ton load. The results were presented in PD Spectrums for concrete and blacktop highways at speeds of 35 and 50 miles per hour. The Dynamic Environment of Spacecraft Surface Transportation, a study’ performed. by Schlue (1966), looked at shock and vibration characteristics to be used in designing transportation vehicles for spacecraft. Comparisons wereinade for vans on three trips over rough roads, irregular roads and smooth highways. The study concluded that air-ride suspension systems are adequate for spacecraft shipment. Preliminary Measurement and Analysis of the Vibration Environment of Common Motor Carriers (Sharpe et a1, 1974) was a research study conducted to find the vibration environment of commercial motor carriers carrying package loads. Some conclusions that were reached were: 1) Only vertical vibrations need to be measured because they are the most severe. 2) Product testing should be performed at various P.D. levels for specified periods of time. Enveloping P.D. 6 data was equivalent to selecting the worst case condition and could result in a severe test requirement. Caruso and Silver's (1976) study, Advances in Shipping Damage Prevention, compared cargo losses in tractor-trailer combinations with similar suspension systems but different; rear wheel position, degrees of loading, road types, and drivers. The conclusions which they arrived at were: 1) P.D. levels for frequencies above 50 Hz. were not significant. 2) Similar suspension systems on different trailers produced similar responses. 3) Different trailer suspension types resulted in a different power density at the first peak, about 5 Hz., but beyond the second peak, about 13 Hz., the power density levels were similar. 4) The worst ride occured on interstate highways at high speeds. 5) Single-leaf steel suspension springs produce the worst ride conditions. 7 6) The worst ride occured in a lightly loaded trailer in which the load was placed over the rear wheels. 7) Different drivers had little effect on the results obtained. Shock and vibration environment studies (Magnuson, 1977 and 1978) were performed on large shipping containers with heavy cargo during truck transportation. The results showed that the vibration history was random and had a normal Gaussian distribution with respect to acceleration levels. It also concluded shipments weighing more than 15 tons showed little difference in vibration amplitude regardless of suspension type. Tevelow, in 1983, summarized twelve previous reports on trucks. He used this to characterize the military logistical transportation vibration environment with respect to the shipment of fuzes using various types of vehicles (truck, sea, rail, and air). Among his conclusions were: 1) The vertical axes almost always has the highest levels of vibration. 2) Specific relationships between vertical, lateral, and longitudinal vibration levels are highly dependent upon the vehicle, suspension, and external conditions. Goff et a1 (1984) reported vertical disturbances caused by large amplitude transients. Accelerometers were mounted on both the truckbed and on packaged products. This was used to monitor the degree of vibration magnification. Data was taken from a half-hour test over city and country roads, interstate expressways, bridges, and railroad crossings. Only accelerations in the rearmost portion of the trailer were recorded. Three different suspension systems were studied: a) Moveable leaf spring tandem axle trailer with the axle at the rear most position. b) Same axle as a), but with axle in forward position. c) Fixed position air-ride tandem axle.trailer. This study found that: 1) Transient accelerations were much more severe than those generated in steady-state vibration. 2) Spring leaf suspension with wheels forward resulted in the roughest ride. 3) Air-ride suspension caused the greatest amplification of vibration inputs by the load. 9 4) The air ride suspension bed had the lowest levels. American President Companies (1986) performed a study comparing double-stack/truck/vessel ride characteristics. Accelerations were recorded while the products were transported. by ship, APL stack train, and truck trailer. Instruments were positioned so that accelerations of each container and product could be recorded. This study showed that vessel transportation generated the lowest acceleration levels during the entire trip. The double-stack intermodal cargo transportation system proved to be the smoothest of available inland transportation modes. Truck shipments remained the highest vibration environment among the tested modes of transportation. Goodwin and Holland (1987) studied the rail distribution environment from Rochester, NY, to Los Angeles, CA, via Chicago, IL. They took into consideration two modes of shipment, Trailer on a Flat Car (TOFC) and Container in a Well Car (CIWC). A change of mode from TOFC to CIWC was made in Chicago. Power Density Spectrums were developed for each of the three axes. Percentages of shocks measured were then reported for similar loading in both modes and four directions, longitudinal, lateral and two vertical axis (rear and front). This study was aimed at expanding the information base on LTL shipments, specifically on low, medium and high 10 natural frequency packages. A knowledge of the effect of truck vibration on the different dynamic characteristics of packages is crucial for the planning of LTL shipments, specifically on the stowage of packages. Goff et a1 (1988) continued to study transient events for trucks having three different suspension types, traveling over "bumpy" roads. The conclusions were: 1) The lading always amplified the product acceleration over that of the trailer bed. 2) An air-ride suspnsion system did not perform significantly better than a spring leaf suspension with the wheels moved all the way to the rear of the trailer, when comparing the largest transient events. 3) The most severe impacts were generated when the rear spring leaf tandem is moved all of the way forward. Dynamic Analysis of a Less Than Truckload Shipment (Marcondes, 1988), studied the response of the truckbed and instrumented packages to a given vibration input. The input was a result of six independent vibration actuators positioned under the truck wheels to vibrate the truck and simulate road conditions. The conclusions reached were: 11 1) For the same input at the axles, the response at the rear of the trailer is 50% larger than that at t h e front. 2) Roadside or curbside locations input little difference along the same axle. 3) The front axle and the fifth wheel also contribute with the input to the truckbed. The front axle contributes about 20% of the vibration input to the rear truckbed. The fifth wheel contributes about 30%. The rear axle contributes the remaining 50%. Measurement of Lateral and Longitudinal Vibration in Commercial Truck Shipments (Antle, 1989) was a study performed to determine the significance of lateral and longitudinal vibrations, in comparison to vertical vibration levels, in truck shipments. These tests were conducted on a variety of road surfaces and at various speeds. The conclusions reached were: 1) The levels of lateral and longitudinal vibration are much less than the vertical vibrations in the same trailer at frequencies below 10 Hz. 12 2) At frequencies greater than 10 Hz., the lateral and longitudinal Spectrums have contours very similar to that of the vertical spectrum. 3.0 EXPERIMENTAL DESIGN To gather the data necessary for this study six different truck shipments were monitored. These shipments were conducted in the Lansing, Michigan area covering the same route as outlined below. Section 1 - School of Packaging to Trowbridge Road Speed limit: 25/35 mph Pavement: Asphalt with cracks Distance: 0.9 miles Section 2 - Trowbridge Road, enter I-496, exit at Grand Ave. Speed limit: 55 mph Pavement: Asphalt Concrete with joints, grooved pavement Distance: 2.4 miles Section 3 - Washington to Mt. Hope Rd. Speed limit: 30 mph 14 Pavement: Asphalt with cracks Distance: 1.0 miles Section 4 - Mt. Hope to Waverly Speed limit: 30 mph Pavement: Asphalt with a few cracks Distance: 2.8 miles Section 5 - Waverly to US-27 Speed limit: 35 mph Pavement: Concrete with joints Distance: 0.4 miles Section 6 - US-27 to Packard Rd. Speed limit: 45/55 mph Pavement: Asphalt with joints Concrete with joints Distance: 14.9 miles Section 7 - Packard Rd. to Clinton Trail (US-50) Speed limit: 45 mph Pavement: Asphalt Distance: 1.4 miles Section 8 - Clinton Trail (US-50) to 08-43 Speed limit: 55 mph 15 Pavement: Asphalt with cracks Smooth asphalt Asphalt with longitudinal cracks Distance: 17 miles Section 9 - 05-43 to US-66 to I-96 Speed limit: 55 mph Pavement: Concrete with joints Distance: 9.7 miles Section 10 - I-96 to College Rd. Speed limit: 55 mph Pavement: Concrete with joints Distance: 39.1 miles Each shipment consisted of a combination of one of two trailer lading weights and one of three suspension systems. The ladings used were: a) 5,000 pounds b) 18,000 pounds The suspensions used were: a) Conventional air-ride suspension (maintained properly) refered to as air up (See Figure 1) b) Damaged air-ride suspension (air bled out) refered to as air down (See Figure 1) 16 c) Conventional leaf spring suspension refered to as leaf (See Figure 2) The following combinations were used for the six shipments: Shipment 1 Trailer: 48 feet x 99 inches (width) x 108 inches (height) Great Dane - Tandem Axle Conventional air-ride suspension (maintained properly) Load: 5000 pounds of miscellaneous computer goods Instrumentation: (See Figure 3) 2 vertical accelerometers - mounted to trailer bed. Front - accelerometer located 55.5 inches from front, inside of trailer, 50.5 inches from the left side of trailer. Rear - accelerometer located 68.0 inches from the inside rear of trailer, 50.0 inches from the left side of trailer. Shipment 2 Trailer: 48 feet x 99 inches (width) x 108 inches (height) Great Dane - Tandem Axle 17 Damaged air-ride suspension (air bled out) Load: 5000 pounds of miscellaneous computer goods Instrumentation: (See Figure 3) 2 vertical accelerometers - mounted to trailer bed. Front - accelerometer located 55.5 inches from front, inside of trailer, 50.5 inches from the left side of trailer. Rear - accelerometer located 68.0 inches from the inside rear of trailer, 50.0 inches from the left side of trailer. Shipment 3 Trailer: 48 feet x 99 inches (width) x 108 inches (height) Great Dane - Tandem Axle Conventional air-ride suspension (maintained properly) Load: 18,000 pounds of miscellaneous computer goods Instrumentation: (See Figure 3) 2 vertical accelerometers - mounted to trailer bed. Front - accelerometer located 55.5 inches from front, inside of trailer, 50.5 inches 18 from the left side of trailer. Rear - accelerometer located 68.0 inches from the inside rear of trailer, 50.0 inches from the left side of trailer. Shipment 4 Trailer: 48 feet x 99 inches (width) x 108 inches (height) Great Dane - Tandem Axle Damaged air-ride suspension (air bled out) Load: 18,000 pounds of miscellaneous computer goods Instrumentation: (See Figure 3) 2 vertical accelerometers - mounted to trailer bed. Front - accelerometer located 55.5 inches from front, inside of trailer, 50.5 inches from the left side of trailer. Rear - accelerometer located 68.0 inches from the inside rear of trailer, 50.0 inches from the left side of trailer. Shipment 5 Trailer: 48 feet x 99 inches (width) x 110 inches (height) Lufkin - Tandem Axle Conventional Leaf Spring 19 Load: 5,000 pounds of miscellaneous computer goods Instrumentation (See Figure 3) Two vertical accelerometers - mounted to trailer bed. Front - accelerometer located 56.0 inches from the front, inside of trailer, 47.5 inches from the left side of trailer. Rear — accelerometer located 68.0 inches from the inside rear of the trailer, 52.0 inches from the left side of trailer. Shipment 6 Trailer: 48 feet x 99 inches (width) x 110 inches (height) Lufkin - Tandem Axle Conventional Leaf Spring Load: 18,000 pounds of miscellaneous computer goods Instrumentation (See Figure 3) Two vertical accelerometers - mounted to trailer bed. Front - accelerometer located 56.0 inches from the front, inside of trailer, 47.5 inches from the left side of trailer. Rear - accelerometer located 68.0 inches from 20 the inside rear of the trailer, 52.0 inches from the left side of trailer. To monitor the truck shipments, piezoelectric accelerometers were used, one for front vertical motion and one for rear vertical motion. These accelerometers were mounted to aluminum blocks and these in turn were screwed to the trailer floor. The sensor type and their sensitivity values are outlined in Table 1. Micro-dot cables were used to connect the accelerometers to Kistler (model 5112) signal conditioners. The output from the conditioner was connected to a Teac XR-310 FM cassette recorder (Figure 4). An oscilliscope was used to perform a cross check and to calibrate the system before each shipment. The recorder was used to record the output from the signal conditioners onto magnetic tapes. During each run, voice input was recorded onto the tape to indicate the begining and ending of each section. Only five sections of the entire shipment. were analyzed, section 3, 6, 8, 9, and 10. This was due to the shortness in length of some sections and that some road surfaces were repeated in the shipments. The experimental design for the analyzed data is outlined in Table 2. vmv -np... . 21 Figure 1. A Typical Air-Ride Suspension 23 sewucucmesuuwcH uo cofiumuoq .m ouswfim mcozmoou couoEoLEoooA‘ _3_:m> i EA 24 Table 1. Accelerometer Information Serial Number Manufacturer Model Sensitivity 14311 PCB 302-A02 9.96 mv/g 14312 PCB 302-A02 10.00 mv/g 25 Teac XR-31O Data Recorder Io ol sesass== 0000000 ll°°°°° . I Oscilloscope BNC Cables Audio Channel _ Kistler Signal Conditions Microdot Cables El—l-\ Accelerometers Figure 4. Setup of Data Acquisition System 26 Table 2. Experimental Design Suspension Section Lading 3 5,000 18,000 6 5,000 18,000 Air-Ride 8 5,000 (properly maintained) 18,000 9 5,000 18,000 10 5,000 18,000 3 5,000 18,000 6 5,000 18,000 Air-Ride 8 5,000 (damaged) 18,000 9 5,000 18,000 10 5,000 18,000 3 5,000 18,000 6 5,000 18,000 Leaf Spring 8 5,000 18,000 9 5,000 18,000 10 5,000 18,000 4.0 DATA AND RESULTS The vibration data recorded on magnetic tape was analyzed using a Schumberger 1209 Random Vibration Analyzer/Conroller and Power Density Plots were printed on a Team TP-35 Video Hard Copy' Printer. These plots were later enlarged and redrawn to aid in the readability of the desired numbers. The random vibration analyzer performs a spectral analysis for a given section of the tape recorded data, and produced a Power Density Value for each component frequency of the spectrum, as described in Appendix A. The Bandwidth used was 1 Hz. for the analysis. Trailer Vibration: Figure 5 shows the background noise levels for the recording and analyzing equipment. The average RMS level for this plot was 0.00192 g. This is about 1.5% of normal RMS values obtained for various trips on different roads. Line current which operates at 60 cycles per second is the cause for the spike at 60 Hz. Figure 6 shows the vertical vibration levels in the trailer caused by the tractor engine running. The levels for this plot showed an average RMS of 0.0398 g. The peak was seen at 50 Hz. 27 28 Tables B-l through B-10, located in Appendix B, show the power density values at specific frequencies for the various road conditions and lading weights used. Figures 7 through 16 show the Power Density Plots that were developed from the same road sections and lading weights. Figures 7 through 16 are located at the end of this section. Due to the fact that all Power Density levels for the front of the trailer were lower than those in the rear, only the values and plots for the rear of the trailer will be presented. Generally, a P.D. plot will be characterized by three main sections. In the 1 - 10 Hz. range, a peak will correspond to the natural frequency of the trailer's suspension system. The levels in this range can result in large displacements and therefore are usually responsible for most damage to products in distribution. A peak in the 10 - 50 Hz. range is historically documented as being caused by the resonant frequency of the trailer structure. In this range there can often be more than one peak due to sub-harmonics of different panels used to make the trailer. Above 50 Hz., a P.D. level of 1.24 x 10‘1 is needed to produce 0.5 g. This will give a stroke of 0.00195 inches (the stroke will even be smaller at frequencies above 50 Hz.). A Power Density level of this magnitude is very difficult to achieve in the distribution 29 system measured in this study. Even if this level is reached, the stroke is so small that damage is unlikely to most packaged products. These peaks are generated by road irregularities. A brief summary of Figures 7 through 16 will now be given. Figure '7 shows vertical. vibration. Spectrums for trailers having air-ride suspension (maintained properly), air ride suspension (damaged), and leaf-spring suspension. All these trailers had a load of 5000 lbs. traveling 30 mph on asphalt with severe cracking (section 3). The air-ride (maintained) spectrum shows a the first peak at 2 Hz., with much smaller peaks at 9 Hz. and 23 Hz. The spectrum for the damaged air— ride suspension had a dominant peak at a frequency of 5 Hz. and smaller peaks at frequencies of 17 Hz. and 30 Hz. Leaf- spring suspension gave a spectrum with a major peak at 4-5 Hz. and smaller peaks at 20 Hz. and 30-40 Hz. The peaks at lower frequencies, 2-5 Hz., correspond to the suspension system of the trailer. Peaks between 10 and 40 Hz. correspond to the trailer structure resonances. Table B-1 shows that the maintained air-ride suspension had significantly lower levels at all frequency levels than that of the damaged air-ride or leaf-spring suspension. The damaged air-ride and leaf-spring suspension had very similar levels at similar frequencies up to 30 Hz. where the leaf-spring suspension then showed slightly higher levels. 30 Figure 8 shows vertical vibration Spectrums for the same suspensions as above with a lading of 5000 lbs., but over asphalt with joints and concrete with joints at vehicle speeds of 45-55 mph (section 6). The spectrum for maintained air- ride suspension showed a suspension response at 2 Hz. and a structural response at a frequency of 19 Hz. The damaged air- ride suspension showed a suspension response at a frequency of 5 Hz. and a structural response at 20 Hz. and 50 Hz. The leaf-spring suspension showed a suspension response at 5 Hz. with structural responses at 20 Hz. and 40 Hz. Table B—2 shows that the maintained air-ride had levels at low frequency which were on the order of 10 times lower than that of the damaged air-ride. The leaf-spring had a Power Density value which was significantly lower than that of damaged air-ride at low frequencies. The levels after 10 Hz. became very similar. Figure 9 shows vertical vibration Spectrums for trailers having a lading of 5000 pounds and the following suspensions: air-ride (maintained properly), air ride (damaged), and leaf- spring. All these trailers traveled 55 mph on asphalt with cracks, smooth asphalt, and asphalt with longitudinal cracks (section 8). The air-ride (maintained) spectrum! shows a suspension response at 2 Hz., with structural responses at 7 Hz. and 20 Hz. and 30 Hz. The spectrum for the damaged air- ride suspension had a suspension resonance at a frequency of 5 Hz. and structural responses at frequencies of 18 Hz., 33 31 Hz., 50 Hz. Leaf-spring suspension gave a spectrum with a response due to suspension at 5 Hz. and structural responses at 17 Hz., 40 Hz. Table B—3 shows that the maintained air- ride suspension had significantly lower levels at all frequency levels. The damaged air-ride suspension had higher levels at low frequencies than that of the leaf-spring. After 6 Hz. the levels became similar. Figure 10 shows vertical vibration spectrums for the three suspensions as above with a lading of 5000 lbs. and traveling over rural roads made of concrete with joints at a speed of 55 mph (section 9). Maintained air-ride suspension showed a suspension response at 2 Hz. and structure response at a frequency of 20 Hz. The damaged air-ride suspension showed a suspension response at a frequency of 4-5 Hz. with structure responses at 19 Hz. and 50 Hz. The leaf-spring suspension showed a response to suspension at 5 Hz. with structure responses at 19 Hz. and 40 Hz. Table B-4 shows that the maintained air-ride had vibration levels at most frequency which were on the order of 10 times lower than that of the damaged air-ride. The leaf-spring gave levels which were lower than that of damaged air-ride at low frequencies. At high frequencies the leaf spring had the highest levels. Figure 11 shows vertical vibration spectrums for trailers having air-ride suspension (maintained properly), air ride 32 suspension (damaged), and leaf-spring suspension. All these trailers had a load of 5000 lbs. traveling 55 mph on concrete with joints (section 10). The air-ride (maintained) spectrum shows no significant response to the trailer suspension although its highest power density value was at 2 Hz. The spectrum for the damaged air-ride suspension showed a response to the suspension at 5 Hz. and a structural response at frequencies of 17 and 37 Hz. The Power Density Spectrum for leaf-spring suspension has a suspension response at 5 Hz. and structural responses at 20 Hz., 30 Hz., and 50 Hz. Table B- 5 shows that the maintained air-ride suspension had vibration levels at all frequencies that were up to 1000 times less than the other suspension systems. The damaged air-ride had a level which was 3 times that of the leaf-spring suspension at low frequencies. At mid to high frequencies the levels for leaf-spring and damaged air-ride were very similar. Figure 12 shows vertical vibration spectrums for the same suspensions as above, with a lading of 18,000 lbs. traveling over asphalt with severe cracks at a speeds of about 30 mph (section 3). The maintained air-ride suspension showed a suspension response at 2 Hz., and structural responses at 10 Hz., 27 Hz. and 33 Hz. The damaged air-ride suspension showed a peak corresponding to suspension at a frequency of 4 Hz. with structural responses at 10 Hz., 17 Hz. and 21 Hz. The leaf-spring suspension showed a peak at 4 Hz. with structural responses at frequencies of 10 Hz., 21 Hz., 40 Hz., and 60 Hz. 33 Table B-6 shows that the maintained air-ride suspension had the lowest power density levels throughout the spectrum. The damaged air-ride had a higher level at low frequencies, after which leaf-spring suspension had the highest power density levels. Figure 13 shows vertical vibration spectrums for trailers having the three different suspension systems. All these trailers had a load of 18,000 lbs. traveling 45 - 55 mph on asphalt with joints and concrete with joints (section 6). The air-ride (maintained) spectrum shows a suspension response at 2 Hz., with structural responses at 20 Hz., 30 Hz., and 50 Hz. The spectrum for the damaged air-ride suspension had a response to suspension at 4 Hz. and structural responses at frequencies of 21 Hz., and 40 Hz. Leaf-spring suspension showed a suspension response with a gradually rising peak from 3 to 5 Hz. and structural responses at 11 Hz. and 40 Hz. Table B-7 shows that all suspensions had similar levels at low frequencies. At frequencies beyond 10 Hz. the leaf-spring suspension showed the highest power density. Figure 14 shows vertical vibration spectrums for the same trailer suspensions with a lading of 18000 lbs., over asphalt with cracks, smooth asphalt and asphalt with longitudinal cracks at a speed of 55 mph (section 8). The P.D. plot for maintained air-ride suspension shows a suspension response at 2 Hz. The damaged air-ride suspension showed a response to :2; 34 suspension at a frequency of 4 Hz. and structural responses at 21 Hz. and 30 Hz. The leaf—spring suspension shows a flat peak from 3 to 5 Hz. due to the suspension with structural responses at 11 Hz., 21 Hz., and 40 Hz. Table B-8 shows the maintained air-ride had levels which were lower than that of the damaged air-ride and leaf-spring, however, the difference wasn't that large. The leaf-spring gave levels slightly higher than that of damaged air-ride at low frequencies and damaged air-ride had a higher level at high frequencies. Figure 15 shows vertical vibration spectrums for trailers having air-ride suspension (maintained properly), air ride suspension (damaged), and leaf-spring suspension. All these trailers had a load of 5000 lbs. traveling 30 mph on asphalt with severe cracking (section 9). The air-ride (maintained) spectrum shows a suspension response at 2 Hz., with much smaller structural response at 9 Hz. and 23 Hz. The spectrum for the damaged air-ride suspension had a response to suspension at 5 Hz. and structural responses at frequencies of 17 Hz. and 30 Hz. Leaf-spring suspension showed a suspension response at 4-5 Hz. and structural responses at 20 Hz. and 30-40 Hz. Table B-9 shows that the maintained air- ride suspension had significantly lower levels then the other two suspensions at all frequency levels. The damaged air-ride and leaf-spring suspension had very similar levels. Figure 16 shows vertical vibration spectrums for the same 35 suspensions as above with a lading of 5000 lbs., but over asphalt with few cracks at a speed of 30 mph (section 10). The spectrum for maintained air-ride suspension showed suspension response at 2 Hz. and a structural response at 19 Hz. The damaged air-ride suspension showed.a much.more severe suspension response at a frequency of 5 Hz. with a structural response at 20 Hz. The leaf-spring suspension showed a peak at 5 Hz. corresponding to the suspension. Structural response was shown at 20 Hz. and 40 Hz. Table B-lO shows the maintained air-ride had levels at low frequency which were on the order of 10 times lower than that of the damaged air-ride. The leaf-spring gave levels slightly higher than that of maintained air-ride up to frequencies of 40 Hz., where the leaf-spring suspension became the worst of the three. Tables 3 and 4 summarize the Power Density values of all data spectrums discussed in the above paragraphs. In general, for a lightly loaded truck a maintained air-ride trailer shows two pronounced peaks, at 2 Hz. and 20 - 30 Hz. The damaged air-ride trailer shows two pronounced peaks, at 5 Hz. and at 20 Hz. Leaf-spring suspension trailers show two pronounced peaks, at 5 Hz. and at 30 - 40 Hz. The vertical vibration levels for the three suspension systems when loaded with a lading of 18,000 pounds, the air-ride (maintained) trailer shows the prominent peak at 2 Hz. The damaged air-ride trailer shows three pronounced peaks, at 4 36 Hz., 20 Hz, and 50 Hz. Leaf-spring suspension trailer shows peaks which are prominant at 4 Hz., 10 Hz., 21 - 22 Hz., 40 Hz. and 50 Hz. The power density spectrums for the damaged.air-ride and leaf- spring trailers follow very similar contours. The explanation for this is that after the air is bled out of the diaphram in a damaged air-ride suspension, the only remaining suspension is shock absorbers. The damaged air-ride often achieves higher power density levels than that of a leaf-spring suspension due to the fact that the suspension will "bottom out" on rougher road inputs. A maintained air-ride suspension will provide lower power density levels, up to 1000 times lower, at all frequencies with a light load. Overall vibration levels are the lowest in air-ride trailers. However, lightly loaded trailers show more pronounced differences between the three suspension types. A damaged air-ride shows a shift in suspension frequency from the conventional air-ride suspension. This shift is from 2 to 5 Hz. due to the stiffening of the suspension. .Also the damaged air-ride has a higher level in the 4-5 Hz. region as compared to the conventional leaf-spring. Even though the structural response of a leaf-spring is the highest at 50 Hz. as compared.to 40 Hz. for the damaged.air-ride, the displacements in this frequency range are however not usually great enough 37 to cause product damage. The effect in lading weight is shown in Figures 17, 18, and 19. A shift in suspension response is shown for both leaf spring and the damaged air-ride system, from 5 Hz. to 4 Hz. The conventional air-ride system showed no effect in suspension response. Typically the power density levels are 3 to 5 times lower with the heavier lading. Figures 20 through 25 demonstarate the ratio of gRMS versus frequency for conventional leaf spring to conventional air- ride suspensions and conventional leaf spring suspensions to damaged air ride suspensions. These plots represent three different road. conditions; Section 3 - intercity’ roads, Section 6 - two lane county roads, and Section 10 - interstate expressway. For instance at an acceleration ratio'of one, the conventional air-ride or damaged air-ride has the same acceleration level as that of leaf spring. At an acceleration ratio of 5 the conventional leaf spring has an acceleration 5 times greater than that of the damaged air-ride or conventional air-ride depending on the respective curve which one is looking at. These curves show a better performance by the conventional air-ride suspension and similar acceleration levels for damaged air-ride and leaf spring. 38 Table 3 - Summary of Responses for 5000 lb. Lading Suspension Frequency (Hz.) P.D. Level Section Air Damaged Leaf Air Damaged Leaf 3 2 5 5 1500 4000 3300 6 2 5 5 9000 70000 20000 8 2 5 5 2000 30000 11000 9 2 5 5 5000 41000 11000 10 2 5 5 1100 50000 20000 Structure Frequency (Hz.) P.D. Level Section Air Damaged Leaf Air Damaged Leaf 3 23 17 20 700 1000 1500 6 20 20 40 1000 3000 6000 8 20 17 17 300 2500 2700 9 20 20 20 330 15000 1500 10 21 20 20 200 2000 2000 All Power Density Levels are x 10* 39 Table 4 - Summary of Responses for 18,000 lb. Lading Suspension Frequency (Hz.) P.D. Level Section Air Damaged Leaf Air Damaged Leaf 3 2 4 4 800 3000 1300 6 2 4 5 5300 15000 5000 8 2 4 5 1100 5000 1300 9 2 4 5 5300 13000 3700 10 2 4 5 4000 10000 2000 Structure . Frequency (Hz.) P.D. Level Section Air Damaged Leaf Air Damaged Leaf 3 10 10 10 530 900 6000 6 20 20 40 900 1300 2000 8 30 21 21 500 1500 1500 9 21 21 21 250 2000 2000 10 20 21 21 210 1100 1100 All Power Density Levels are x 10* 40 1 x10‘“ Ii 1: \ C! CD a z u: o a: m 3 O a -14 1x10 1 Figure 5. FREQUENCY(H2) Vertical Rear Trailer Vibration: Background Noise for Analyzing Equipment 41 1 x10" l Bi E . “a: \\ / \fl E g \ ,— /\..V/VJ \l 0 1.1 kw a c: m 3 O a. 1 x1610 1 FREQUENCY (Hz) ‘C'C Figure 6. Vertical Rear Trailer Vibration: Engine Noise for Stationary Truck 42 Key — Air Up -- Air Down --- Leaf ‘- E \ ./""\ . “or // , 0’ W\ filly f4 "'x - 2".I \. / .\ 4’ ‘ .4J \ ir' . E; ‘_.—' ::,/” V:>" \ \ 16’ ’/)K\‘ \ \ I ‘1‘5 tn :‘1/ ”V0 / / - i E \/’ . D 1: Ill 3 O Q 1 “0'31L 1 FREQUENCY (Hz) Figure 7. Vertical Rear Trailer Vibration for Asphalt With Severe Cracks, 30 mph (Section 3); Load: 5000 lbs. 43 Key — Air Up —- Air Down --- Leaf 1 I’ \ /- E .. t 7/ \ 1.x, / \‘M J\ g \ / LU o m Ill 3 O D. 1 ado-3% FREQUENCY (Hz) 1' "c Figure 8. Vertical Rear Trailer Vibration for Asphalt With Joints, Concrete With Joints, 45-55 mph (Section 6); Load: 5000 lbs. 44 NW -—-AkUp - - Air Down --- Leaf ul \ \I A} \ ab POWER DENSITY 92/112 / I \ ll é‘ -.L 1x10 1 FREQUENCY (Hz) l 00 Figure 9. Vertical Rear Trailer Vibration for Asphalt With Cracks, Smooth Asphalt, 55 mph (Section 8); Load 5000 lbs. 45 Key — Air Up -- Air Down --- Leaf ‘- "|\ ’1 .3. E I, ’ ‘i .r \x’ 1 . in C” 15" // “ml. 1 : ,’/";’ \ xN “\ ’7 Vzi-lv“. “(W — r,,' "a \5/ ‘1 g ’ \ / \ i V Ill \ ‘NW D I Ill 3 O O. -8 1x10 1 FREQUENCY (Hz) 100 Figure 10. Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 9); Load: 5000 lbs. 46 kw -—-AkUp -- Air Down --- Leaf 1 ’4 \ /.W¢ N 1’: ‘-‘, I. A . 23 ,7 \ .‘4 ./ \ \I “U! / 'Il \ ’1/\.‘ 7" '. I .\ t //;”l ‘1. [1" \\II" V i" V I‘J" _ x” \::.--;- ' g \ ‘- - AV 1 m \ /\ l [‘1 VJ a x \_ m Ill 3 O :1. —al 1 x10 1 ilOC FREQUENCY (Hz) Figure 11. Vertical Rear Trailer Vibration for Concrete With Joints, 55 mph (Section 10); Load: 5000 lbs . 47 Key — Air Up —- Air Down --- Leaf ‘- E . .Ix. \ I NC! I”: “\'\ \‘. .4’ ‘. t /.-7~ /> ‘1 1‘. I — I" I ~‘1 0‘ A ,3- m r;” \ \‘ VIA/ \ \.\! flAy\i f ‘IV ,1 Z ’ / I In a ,/ VJ a: Ill 3 O a. -8 1 x 10 1 FREQUENCY (Hz) 1' 0" Figure 12. Vertical Rear Trailer Vibration for Asphalt With Severe Cracks, 30 mph (Section 3); Load: 18,000 lbs. 48 Key -— Air Up - - Air Down --- Leaf ’ \ .i\ °\\ /‘- \‘5 >2 , \ POWER DENSITY 92/112 K.‘\ 1 x10’8 1 FREQUENCY (Hz) ‘°° Figure 13. Vertical Rear Trailer Vibration for Asphalt With Joints, Concrete With Joints, 45-55 mph (Section 6); Load: 18,000 lbs. 49 Key — Air Up -- Air Down --- Leaf 1 53 /\ ‘. 1b OE) /\ I‘fi" INK 'P'./~-/."\\.\ I, \ [P‘IA‘VA 2K \\ I. f\ '\‘-I'\\ E 43/ \ \V y I I I, \ \.I y" \ \AMN m ’l/II/ \—\ [I A :2 /' ‘N.a \/ ‘\J/ “ ' V 21 \ a: r" Ill 3 O :1 1 x10-81 10c FREQUENCY (Hz) Figure 14. Vertical Rear Trailer Vibration for Asphalt With Cracks, Smooth Asphalt, 55 mph (Section 8); Load: 18,000 lbs. SO Key — Air Up -- Air Down --- Leaf 1 g /\