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Project P07110 - Vertical Test Stand Mechanical Design & Analysis Team Guide: Dr. Jeﬀrey Kozak Start Term: 2006-2 1 Contents I Mechanical Calculations 3 1 Introduction 3 2 Initial Design Constants 3 3 Tapered Roller Bearing Assembly 3 3.1 Tapered Roller Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2 Bolts Holding Bearing Case Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2.1 Summary of Standard Bolt Preloads . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2.2 Bolt Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3 Shaft in Bearing Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3.1 Initial Hand Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3.2 FEA Analysis of Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Universal Joint 8 4.1 FEA Analysis on Modiﬁed Universal Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2 Shearing In Bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5 Load Cell Connection to Rocket Assembly 12 5.1 Tension and Compression in Bolt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2 Shear of Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2.1 One Thread Carries Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.2.2 20 Threads Carry Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6 Frame 14 6.1 Stress in Frame Uprights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.2 Weld at Base of Frame Uprights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 II Risk Assessment 17 7 Risk Management Philosophy 17 8 Standards for the Ranking of Hazardous Conditions 18 9 Standards for the Probability of a Hazardous Condition Occurring 18 10 Hazards in the Design 19 10.1 Frequent Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 10.2 Probable Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 10.3 Occasional Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 10.4 Remote Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 10.5 Improbable Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 11 Risk Management Summary 20 2 Part I Mechanical Calculations 1 Introduction The responsibility of the P07110 - Vertical Test Stand Team is to create a design for a vertical test that meets the requirements necessary of other teams in the METEOR project. The main purpose of the vertical test stand is to provide accurate test data to the P07106 - Guidance and P07109 - Flying Rocket teams so that they can design and optimize the rocket. To accomplish this the test stand will have to safely constrain the rocket. This is necessary to prevent injury to people in the vicinity of the test stand and damage to other testing equipment. This document outlines the design process and calculations for the vertical test stand that our team is creating. At this point certain aspects of the design are contingent on the physical design of the actual rocket, so the test stand team will be and has been working closely with the Flying Rocket team. The current design will be subject to scrutiny and reﬁnement because of the progressive nature of the design process. In light of this, many of the intricate details of our test stand design have deliberately been left vague in order to accommodate whatever needs that may arise from the Flying Rocket and Guidance teams. Calculations are given in this report to justify and support our team’s design decisions. Some of the factors of safety in the calculations are abnormally large because of the need to provide ease of assembly and use of the ﬁnal design. This data is purposely included though, to provide a record of and an engineering justiﬁcation for the vertical test stand design. 2 Initial Design Constants The table below summarizes the initial a priori design speciﬁcations that the vertical test stand is being tailored to. These constraints and guidelines were formed for two reasons. They provide a starting point for our team’s calculations and serve to deﬁne the relationship that our project has with other projects in the METEOR program. Speciﬁcation Value Maximum Rocket Diameter 12 in Maximum Rocket Length 50 in Estimated Plume Length 3 ft Maximum Rocket Thrust 200 lbf Maximum Rocket Weight (including fuel) 50 lbf Maximum Lateral Force Expected 25 lbf Maximum Roll Moment Expected 100 in-lbf 3 Tapered Roller Bearing Assembly 3.1 Tapered Roller Bearings Two tapered roller bearings mounted in series provide freedom of roll movement; this is shown in ﬁgure 1 on the following page. Tapered bearings were selected because the shaft coming from the universal joint will see a torque and an axial force. Since the axial force will change in direction depending on whether the rocket is hanging from the stand or ﬁring with an upward thrust, two bearings were used. In light of the fact that the bore of the universal joint is 1 in., the bore of the tapered bearings were selected to be 1 in. 3 Figure 1: Diagram of tapered roller bearing assembly. Elaborate engineering analysis was not done on the bearings because they will not support a con- stantly rotating shaft. The supplier of the bearings gives dynamic load capacities of 1620 lbf in the radial direction and 1040 lbf in the axial direction. Both of these values are well within any loading expected to be placed on the bearings. 3.2 Bolts Holding Bearing Case Together A bolt pattern, around the outer edge of the tapered roller bearing case, was decided as the method for holding the top and bottom of the bearing case together. For engineering simplicity, it was also decided to use a fastener going through the bearing case and terminated with a nut and washer. Figure 1 shows how the bolts go though the bearing case. The design criteria chosen is to design the bolted joint so that enough preload is developed in the bolts to prevent the three sections of the bearing case from separating in any loading case apt to occur. At this point in the design, the only concrete loading data is that the maximum expected thrust of the rocket is 200 lbf and the maximum weight of the fueled rocket will be 50 lbf . An unknown piece of loading data is the weight of the testing apparatus connecting the rocket to the load cell. The total load placed on the rocket will be the net sum of the three forces described above. Additionally, it can be said that the rocket thrust will act in the opposite direction of both the weight of the rocket and the testing apparatus. Therefore, if the combined weight of the rocket and testing apparatus are less than the rocket thrust, the net force never exceed the magnitude of the thrust force. We feel that using the maximum thrust force as the design load on our test apparatus because we feel it is very reasonable to assume that the weight of the rocket and testing apparatus will not be greater in magnitude than the rocket thrust. 3.2.1 Summary of Standard Bolt Preloads The preloads (Fi ) obtainable for a standard reusable bolted joint containing are given in table 1 on the following page for fasteners ranging in size from #6 to 1/4 in. The decision to use stainless steel fasteners is made up front because of the corrosion resistance that stainless steel provides. With this in 4 Table 1: Summary of developed bolt preloads. Size At (in2 ) Fi (lbf ) #6-32 .00909 231.8 #6-40 .01015 258.8 #8-32 .0140 357.0 #10-24 .0175 446.3 #10-32 .0200 510.0 1/4”-20 .0318 810.9 1/4”-28 .0364 928.2 mind, the proof strength (Sp ) of the stainless steel fasteners used is 34 ksi. This value was obtained by using the relationship that the proof strength is generally equal to 85% of the tensile yield strength of the fastener material. Fi = .75At Sp , At ≡ standard tensile stress area 3.2.2 Bolt Sizing From table 1 it can be safely said that many of the bolt sizes given will satisfy the necessary requirements. So that a symmetric clamping force is applied to the end plates of the bearing case, a bolt pattern of 4 bolts was selected. The size of the bolts selected are #10-24 because they provide a balance between overall strength of the bolt and the bearing case. Using the the preload results obtained before, the ﬁnal total preload force holding the bearing case together is computed to be about 1785 lbf . If the net force created by the rocket during testing is transferred as a thrust into the bearings, then the tendency of this force will be to try to pull the bolted connection between the three components of the bearing case apart. Our design case uses a design load, F, equal to the maximum thrust of the rocket. This leads to a factor of safety, against separation of the components of the bearing case, of 8.9. ΣFi 1785 lbf n= ⇒n= ⇒ n = 8.9 F 200 lbf 3.3 Shaft in Bearing Case On the shaft inside the bearing case there is a shoulder that supports the weight of the rocket and any thrust forces during the rocket ﬁring. Stress concentrations occur at changes in diameters of shafts and the bolt holes that connect the shaft to the universal joint. Initial hand calculations and then FEA models were run on the shaft because of the stress concentrations. 3.3.1 Initial Hand Calculations The hand calculations were done assuming a 200 lbf tensional load applied to the shaft. Only the tension case was analyzed because common stress concentration factor charts only provide data for loading in tension. In addition the tensional loading cases generally result in higher stress states. Figure 2 on the following page shows the dimensions required for the shaft to ﬁt in the bearing housing and the variables that those dimensions correspond to in the stress concentration factor equations. The stress concentration in the shoulder region of the shaft is dependent on the ratio of the two shaft diameters and the ﬁllet radius between those diameters. These diameters and the ﬁllet radius were 5 Figure 2: Dimension schematic for hand calculation of bearing case shaft stress calculations. determined from the conﬁnes of the bearings. Using ﬁgure A-15-7 in Mechanical Engineering Design the value of the stress concentration factor was visually determined. D 1.375 in r .050 in = = 1.375 = = .050 ⇒ Kt,shoulder = 2.2 d1 1 in d1 1 in This stress concentration factor is then applied to the the basic formula for pure tensional stress in the region of the minor diameter of the shaft. F d1 200 lbf σ = Kt,shoulder , A = π( )2 ⇒ σ = 2.2 • 1 in 2 ⇒ σ = 560 psi A 2 π( 2 ) Since there may be play in the drilled bolt holes at the end of the shaft, it is possible for only one hole to carry the entire load placed on the shaft. Accordingly the calculation assumes this fact. The stress concentration factor was again visually determined using ﬁgure A-15-1 in Mechanical Engineering Design. In the formula below Amin refers to the minimum cross sectional area of the shaft at the hole and this value was calculated to be approximately equal to .319 in2 . d2 .5 in = = .5 ⇒ Kt,hole = 2.2 d1 1 in F 200 lbf σ = Kt,hole ⇒ σ = 2.2 • ⇒ σ = 1379 psi Amin .319 in2 3.3.2 FEA Analysis of Shaft Models were run for a 200 lbf force in compression and tension applied at the bolt connection closest to the end of the shaft. The shoulder of the shaft was ﬁxed. The material was chosen as AISI 304 stainless steel shaft with a yield strength of 32 ksi. Figure 3 on the next page shows the results from the tension case. The maximum von Mises stress in tension was 2756 psi, resulting in a factor of safety of 11. Figure 4 on the following page shows the results from the compression case. The maximum von Mises stress in compression was 1509 psi, resulting in a factor of safety of 21. A third case, where a 100 in-lbf moment was applied to the bottom of the shaft, was also run to simulate seizure of the taper bearings. Figure 5 on page 8shows this and the maximum von Mises stress in this case was 5438 psi. In this case the resulting factor of safety was 6. 6 Figure 3: FEA model of bearing shaft in tension. Figure 4: FEA model of bearing shaft in compression. 7 Figure 5: FEA model of bearing shaft under 100 in-lbf torque. 4 Universal Joint A Curtis universal joint was selected to provide freedom of lateral movement for the rocket. The 2 in. universal joint comes with a 1 in. bore for mounting the shaft from the tapered roller bearing case to the universal joint. The manufacturer of the universal joint gives maximum loads that the joint can withstand. Additional analysis was also done on the universal joint because the design requires modiﬁcation of the stock universal joint. The manufacturer of the universal joint gives a static maximum torque rating of 22000 in-lbf and a maximum axial force value of 25000 lbf . Both of these values are so large that they are not limiting factors to the design. It is desired though to drill two holes into the universal joint to attach the shafts however, so an FEA analysis was done on the modiﬁed universal joint. 4.1 FEA Analysis on Modiﬁed Universal Joint Two FEA models were run on the modiﬁed universal joint yoke. One assumed a 200 lbf compression loading and another assumed a 200 lbf load in tension. Both models used the constraint that the center pin of the universal joint remained ﬁxed. It is entirely possible for only one of the bolts between the bearing case shaft and and the modiﬁed universal joint yoke, so the models were run with the 200 lbf load applied to the hole closest to the opposite end of the universal joint. The force was placed at this location because it is of importance to gain insight to the stress ﬂow around the other hole in the shaft. The yoke was assumed to be made out of alloy steel with a yield strength of 90 ksi. Results for the compression case are shown in ﬁgure 6 on the following page. In compression the maximum von Mises stress in the part was 778 psi. This yields a factor of safety of 115. 8 Figure 6: FEA analysis for compression case. 9 Figure 7: FEA analysis for tension case. Figure 7 shows results for the FEA model involving tension. The maximum von Mises stress for this case is 2341 psi, resulting in a factor of safety of 38. 4.2 Shearing In Bolts As explained in the previous section, the worst case scenario is for one of the bolts shown in ﬁgure 8 on the following pageto be carrying the entire 200 lbf load. Another worst case scenario assumption is that the loading was applied as a pure shear load over the minor area in the threaded portion of the bolt. SAE Grade 8 1/2”-20 bolts were selected for this joint. A ﬁne thread series and Grade 8 rating were selected for maximum strength. Figure 9 on the next page shows a free body diagram for the bolt as analyzed. Since the bolt is in double shear, the total shear force being applied across each load bearing section of the bolt is 100 lbf . The minor area of the bolt that the shear force is applied over is As =.1486 in2 . Using these conditions the shear stress in the bolt is calculated below. Fs 100 lbf τs = ⇒ τs = ⇒ τs = 673 psi As .1486 in2 10 Figure 8: Bolts through universal joint. Figure 9: Free body diagram for bolt through the universal joint. 11 Figure 10: Bolt connecting load cell to rocket assembly. The resultant shear force of 673 psi is very small. For calculating the resultant factor of safety Distortion-Energy Theory was used to predict the shear yield strength based on the known tensile yield strength. That relationship is that the shear yield strength is approximately equal to .577 times the tensile yield strength. For a Grade 8 bolt the minimum yield strength in tension is 130 ksi. Now the resultant factor of safety is calculated for the bolt to be 111. Sy,s ≈ .577Sy,t ⇒ Sy,s = .577 • 130 ksi ⇒ Sy,s = 75.0 ksi Sy,s 75.0 ksi n= ⇒n= ⇒ n = 111 τs 673 psi 5 Load Cell Connection to Rocket Assembly The connection between the rocket assembly and the vertical load cell needs to be analyzed because only the load cell only accepts one 1/2” bolt (location shown in ﬁgure 10). Therefore there is only one point of connection ultimately holding the rocket up. In light of this fact the bolt and threads of this connection were heavily analyzed. The load cell is threaded to accept a 1/2”-20 bolt as the member that actually connects the load to be measured to the load cell. Therefore, the size of the bolt is a driven quantity. One design choice that we could make was to specify a SAE Grade 8 bolt for this connection. This will provide maximum possible strength. Table 2 on the next page provides a neat summary of the minimum strength values, for Grade 8 bolts, used in our calculations. 12 Table 2: Strength properties of SAE Grade 8 bolts. Property Minimum Allowable Value Proof Strength (Sp ) 120 ksi Yield Strength (Sy ) 130 ksi Tensile Strength (St ) 150 ksi 5.1 Tension and Compression in Bolt For failure analysis purposes the bolt can be analyzed as it is carrying the net load entirely in tension or compression on the standard tensile stress area (At ) of the bolt. From a stress analysis point of view, one of the design targets in a bolted connection is to have maximum stress state in the bolt that is less than the proof strength of the bolt. The load factor of an externally loaded bolt is generally calculated as the ratio of the proof strength of the bolt to the stress state created in the bolt as the result of an external load. In a bolted connection the net stress state in the bolt is made up of several diﬀerent factors. Those factors are the external load applied to the bolted connection (P), the fraction of the external load carried by the bolt (C), and the preload force developed in the bolted connection (Fi ). Our postulation that the entire load could be carried in tension on the bolt area is a possible situation because this could happen if the bolt was not tightened with a preload. In this case Fi =0, by deﬁnition, and C=1 because the entire external load would be carried by the bolt. C can only be less than one in cases where and elastic reaction force is developed in the members as a result of the clamping reaction of the bolt. Taking into account the parameters of our design case, the general equation for the load factor of a bolt can be simpliﬁed. S p At − F i S p At n= ⇒n= CP P Our design case assumes an external load (P) of 200 lbf and the standard tensile stress area (At ) of a 1/2”-20 bolt is .1599 in2 . The ﬁnal calculation for the load factor equals 95. S p At 120 ksi • .1599 in2 n= ⇒n= ⇒ n = 95 P 200 lbf 5.2 Shear of Threads The other possible area of failure is if the internal threads of the hole that the bolt going through the load cell shear oﬀ (strip). The bolt itself was selected to be SAE Grade 8, and the shaft material that the bolt is going to thread into is going to be annealed AISI 304 stainless steel. Of the two thread materials, the stainless steel has the lower tensile yield strength. The tensile yield strength (Sy,s ) of AISI 304 stainless steel is 40.0 ksi. Again using the Distortion-Energy Theory, the shear yield strength (Ss,y ) of AISI 304 stainless steel was approximately calculated to be 23.1 ksi. Sy,s ≈ .577Sy,t ⇒ Sy,s = .577 • 40.0 ksi ⇒ Sy,s = 23.1 ksi The other piece information needed for developing an analytical expression for the shear on the thread(s) is the area that the shear force acts upon. This area is a function of the thread pitch (p), thread root diameter (dr ), and percentage of engagement between the internal and external threads (wi ). For a UNF 1/2” thread the thread pitch is .05 in, the root diameter is .435 in, and the percentage of engagement is 80%. Using an expression for the circumference of the thread and the known values previously stated, the area that the shear force acts on for a single thread (As ) is calculated to be .055 in2 . As = πdr wi p ⇒ As = π • .435 in • .80 • .05 in ⇒ As = .055 in2 13 If the maximum permissible shear stress is set equal to the shear yield strength and the shear stress equation is resolved for the external load (F) an expression for the maximum force (Fmax ) that the thread(s) will support is derived. nt is the number of engaged threads in the joint. F τmax = ⇒ Fmax = Sy,s nt As As Two cases were explored in our analysis. The ﬁrst case assumes that the entire load is carried by a single thread and and the second case assumes that 1 in of tapped hole or 20 threads carry the load. 5.2.1 One Thread Carries Load Fmax = Sy,s nt As ⇒ Fmax = 23.1 ksi • 1 • .055 in2 ⇒ Fmax = 1270 lbf Using the design load (F) and the maximum load (Fmax ) an expression and value for the factor of safety in this case is found to be 6.3. Fmax 1270 lbf n= ⇒n= ⇒ n = 6.3 F 200 lbf 5.2.2 20 Threads Carry Load The calculated factor of safety in this case is 127. Fmax = Sy,s nt As ⇒ Fmax = 23.1 ksi • 20 • .055 in2 ⇒ Fmax = 25410 lbf Fmax 25410 lbf n= ⇒n= ⇒ n = 127 F 200 lbf 6 Frame The vertical test stand design utilizes a frame to hang the rocket from and attach the sensors to. A preliminary CAD model of the vertical test stand with the frame highlighted is presented in ﬁgure 11 on the following page. All analysis done on the frame assumes that a very weak structural steel was used in the construction of the frame. Using this approach allows the use of stronger materials for increased factors of safety if necessary later on. The steel type for the calculations is AISI 1040 hot rolled steel. The speciﬁed minimum yield strength of this steel is 42 ksi. 6.1 Stress in Frame Uprights Three 6” X 25 lbf /ft wide ﬂange I beams were selected to be the uprights for the frame. The design proposal assumes that the two tallest uprights are roughly 9 feet high. With regards to analysis, the main area of concern with the frame is that people or equipment could lean up against the frame. Forces applied perpendicular to the web of the upright will result in higher bending stresses in the beam than forces applied along the web of the beam. Analysis will focus on a force applied perpendicular to the web because the stress will be higher. For the design case, a 400 lbf force was applied, as shown in ﬁgure 12 on page 16, to the top of the tall upright. The maximum bending stress was then found at the base of of the beam. M is the resultant bending moment for a force, F, applied at a distance, d, from the plane of analysis. Since the beam selected is a standard shape values for cmax and I were obtained from tables. cmax =3.040 in and I=17.1 in4 . M = F × d ⇒ M = 200 lbf × 20 in ⇒ M = 4000 lbf • in 14 Figure 11: CAD model of test stand design with frame highlighted. M cmax 4000 lbf • in × 3.040 in σmax = ⇒ σmax = ⇒ σmax = .711 ksi I 17.1 in4 A factor of safety against yielding can now be computed based on the yield strength of the steel and maximum stress just calculated. Sy 42 ksi n= ⇒n= ⇒ n = 59 σmax .711 ksi 6.2 Weld at Base of Frame Uprights To secure the frame uprights to the ground, it is desired to weld square plates to the bottom of the frame uprights (see ﬁgure 13 on the following page). Since this weld is in a comparatively high stress area, compared to the rest of the frame, it is desired to use a butt weld with complete joint penetration. This will take more eﬀort to construct, but will yield a weld with strength comparable to that of the base metals. According to AISC (American Institute of Steel Construction) guidelines, weld joints subjected to bending stresses should conservatively have a maximum stress at the weld that is no greater than 60% of the minimum yield strength of the metal(s) in the weld joint. If materials of several diﬀerent yield strengths are present in the weld then the lowest yield strength among the individual materials should be used. Most common ﬁller metals for steel have higher yield strengths than than the minimum yield strength of the steel used in the frame design, so the frame material is the limiting factor. Sy,weld = .60 × Sy,min ⇒ Sy,weld = .60 × 42 ksi ⇒ Sy,weld = 25.2 ksi Since complete joint penetration is being used in the welds the area of the weld area is at least as large as the cross section of the beam. Since there is no area reduction, the maximum stress calculated in section 6.1 on the previous page is representative of the stress in the weld. With this a factor of safety can be calculated for the weld. Sy,weld 25.2 ksi n= ⇒n= ⇒ n = 35 σmax .711 ksi 15 Figure 12: Force applied to beam for stress computation. Figure 13: Detail of plate welded to frame upright. 16 Figure 14: Steel tube surrounding the rocket (concrete bunker not shown for clarity). Part II Risk Assessment 7 Risk Management Philosophy Current and future rockets constructed by the METEOR project are all experimental devices. Sound judgment and scientiﬁc knowledge is applied during the design of the rockets, however, there is still an uncertainty in knowing what exactly is going to happen when a rocket engine ﬁres. In light of this fact, our team has come up with a plan that lists the risks present and then describes the measures being taken to mitigate the risks. It should be noted that the safety analysis done by the vertical test stand team builds on previous safety analysis done for the METEOR project. These shared safety measures provide proven strategies for dealing with the hazards of rocket testing; which in turn brings on less new risk. The basic mentality that our team has taken in developing the plan to manage the uncertainty in rocket testing, is to have engineering and physical barriers in place to help contain the hazards. From an engineering standpoint safety was built into the design and excess strength exists in the structural design. Physical barriers are also present to help contain any uncontrolled occurrences that may occur during a test. The ﬁrst of those is a steel tube that surrounds the rocket, shown in ﬁgure 14, to help minimize property damage inside the concrete building that testing is done within. The concrete building itself is another safety measure. This structure was put in place by a previous METEOR team to help contain the rocket during testing. Our test stand holds the rocket in the vertical orientation with the thrust forcing the rocket upward. As a safety measure there is only a 2 inch diameter hole in the top of the concrete bunker. As shown in ﬁgure 15 on the next page, this hole allows the 1 inch shaft that supports the rocket to connect to the load cell, but will not allow the rocket to come out the top of the concrete bunker. 17 Figure 15: Hole in the top of the concrete bunker. 8 Standards for the Ranking of Hazardous Conditions Hazardous conditions are categorized based on the severity of the outcome experience for a particular condition. The framework below shows the standardized categories, and the consequence criteria for each category. Category Description Environmental Health and Safety Results I Catastrophic Could result in death, permanent total disability, loss exceeding $1,000,000, and/or irreversible severe environmental damage that violates law(s) or regulation(s). II Critical Could result in permanent partial disability, injuries or occupational illness resulting in the hospitalization of at least three personnel, loss exceeding $200,000 and less than $1,000,000, and/or reversible severe environmental damage that violates law(s) or regulation(s). III Marginal Could result in injury or occupational illness resulting in one or more lost work day(s), loss exceeding $10,000 and less than $200,000, and/or mitigatable environmental damage that does not violate and law(s) or regulation(s) where restoration can be accomplished. IV Negligible Could result in injury or illness not resulting in a lost work day, loss exceeding $2,000 and less than $10,000, and/or minimal environmental damage not violating any law(s) or regulation(s). 9 Standards for the Probability of a Hazardous Condition Oc- curring The probability of each hazardous condition occurring is also rated according to a standardized scale. That scale is described below. 18 Level Description General Probability of Occurrence A Frequent Continuously experienced. B Probable Occurs frequently. C Occasional Will occur several times. D Remote Unlikely, but can be expected to occur. E Improbable Unlikely to occur, but possible none the less. 10 Hazards in the Design The hazards for this project were collected and are explored in detail in the following subsections. To help with the ranking of the hazards, they were separated into groups based on their probability of occurrence. Each subsection contains a diﬀerent probability of occurrence. 10.1 Frequent Hazards Hazard Category Probability Control Residual Risks Bunker ﬁlls IV A Persons not allowed in bunker until Equipment with smoke / smoke clears after testing. Damage exhaust. 10.2 Probable Hazards None 10.3 Occasional Hazards Hazard Category Probability Control Residual Risks Burning chunks III C Floor of bunker is concrete and thus not None of material is ﬂammable. ejected from rocket during test. Coupling to III C Secure attachment will be checked for in Equipment rocket loosens pre-test inspection and the rocket will be Damage or breaks. contained in the concrete bunker. 19 10.4 Remote Hazards Hazard Category Probability Control Residual Risks Rocket plume II D Flammable material will be cleared Small Fire or exhaust around the test stand and a NYS Vol- ignites sur- unteer Fireﬁghter will be present during roundings. tests. Small animal IV D Testing bunker is enclosed on 5 of 6 sides None enters test and this occurrence would not be detri- area. mental to the test or any observers. Person enters II D People will not be allowed into the bunker None bunker while it until exhaust clears. is ﬁlled with smoke / exhaust. Failure of III D Acceptable factor of safety exists in the Equipment bolted design and a load rated bolt is being Damage connection at used for the this connection. Rocket will load cell. be contained within the concrete bunker. Connection to IV D Rocket would be still held by the main Equipment one or more of coupling. Furthermore the rocket would Damage the lateral load be contained within the bunker. cells breaks. Rocket II or III D Rocket will be well contained within the Equipment becomes bunker. If it exits through the port in Damage, Small totally the bunker for the exhaust, that will be Fire unconstrained facing away from the test observers. within the bunker. 10.5 Improbable Hazards Hazard Category Probability Control Residual Risks Tapered roller IV E Bearings have load ratings well in excess None bearing(s) of what is expected. Our mechanical seize. design also will withstand this occurrence. 11 Risk Management Summary The major item of note from our risk assessment is that the residual risks present all concern damage to property and life. While steps were taken during the design, and will be taken in the future during the testing procedure to minimize damage to equipment and the environment the potential for damage still does exist. Hopefully, any undesirable occurrence during testing would be contained by the steel tube surrounding the rocket in order to cause as little damage as possible. In addition, the predominantly wet and swampy land around the concrete bunker where the rocket is tested would serve to limit the spread of a brush ﬁre. 20

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