Lesson 14 Test Method for Product Fragility 第14课产品脆值试验方法
Lesson 14 Test Method for Product Fragility 第14课 产品脆值试验方法
Test Method for Product Fragility o a shock machine is used to generate a damage boundary curve o a vibration system is used to map out the natural frequencies of a product
Test Method for Product Fragility ⚫ A shock machine is used to generate a damage boundary curve ⚫ A vibration system is used to map out the natural frequencies of a product
Shock: Damage Boundary Shock damage to products results from excessive internal stress induced by inertia forces Since F=ma shock fragility is characterized by the maximum tolerable acceleration level, i. e, how many gs the item can withstand Why damaged? How to reduce g's? The packaging material changes the shock pulse delivered to the product so that the maximum acceleration is greatly reduced(and the pulse duration is many times longer) The package designers goal To be sure that the g-level transmitted to the item by the cushion is less that the g-level which will cause the item to fail
Shock: Damage Boundary Shock damage to products results from excessive internal stress induced by inertia forces - Since F=ma, shock fragility is characterized by the maximum tolerable acceleration level, i. e, how many g’s the item can withstand. - Why damaged? - How to reduce g’s ? The packaging material changes the shock pulse delivered to the product so that the maximum acceleration is greatly reduced (and the pulse duration is many times longer). - The package designer’s goal: To be sure that the g-level transmitted to the item by the cushion is less that the g-level which will cause the item to fail
Shock: Damage Boundary The damage boundary theory is used to determine which shock inputs will cause damage to a product and which will not Two parts of a shock can cause damage 1. the acceleration level a 2. the velocity change Av(the area under the acceleration-time history of the shock, thought as the energy contained in a shock The critical velocity change(AVc): a minimum velocity change Which must be achieved before damage to the product can occur 1. Below AVc, no damage occurs regardless of the input a 2. EXceeding AVc, does not necessarily imply that damage results a If Av occurs in a manner which administers acceptable doses of acceleration to the product, the velocity change can be very large without causing damage b If Avc and Ac are both exceeded, damage occurs Figure 14.1: Typical damage boundary curve
Shock: Damage Boundary The damage boundary theory is used to determine which shock inputs will cause damage to a product and which will not. - Two parts of a shock can cause damage: 1. the acceleration level A 2. the velocity change ∆V (the area under the acceleration-time history of the shock, thought as the energy contained in a shock) - The critical velocity change(∆Vc): a minimum velocity change which must be achieved before damage to the product can occur. 1. Below ∆Vc, no damage occurs regardless of the input A 2. Exceeding ∆Vc, does not necessarily imply that damage results. a. If ∆V occurs in a manner which administers acceptable doses of acceleration to the product, the velocity change can be very large without causing damage. b. If ∆Vc and Ac are both exceeded, damage occurs. Figure 14.1: Typical damage boundary curve
Shock: Damage Boundary Implications of Fig. 14.1 a. if the input avthe product's AVc, However, the only way to avoid damage is to limit the input a< the cushioned package performs: it translates the higa product's AC. This is usually one of the functions that acceleration events experienced on the outside of the container to lower acceleration events experienced inside at the unit
Shock: Damage Boundary Implications of Fig.14.1: a. if the input ∆Vthe product’s ∆Vc, However, the only way to avoid damage is to limit the input A < the product’s Ac. This is usually one of the functions that a cushioned package performs: it translates the high acceleration events experienced on the outside of the container to lower acceleration events experienced inside at the unit
Shock: Damage Boundary 9oEaoz Damage N。 Damage Figure 14.1 Typical damage boundary curve
Shock: Damage Boundary Figure 14.1 Typical damage boundary curve
Shock: Damage Boundary c.For△V<△vc, area where damage does not occur even with very high accelerations. Here Av(drop height is so low that the item acts as its own shock isolator d. <Ac damage does not occur. even for large av That's because the forces generated(F =ma) are within the strength limits of the products From Fig 14.2 a AVc boundary(vertical boundary line), is independent of the pulse wave shape b Ac to the right of the vertical line) for half sine and sawtooth pulses depends upon AV
Shock: Damage Boundary c. For ∆V< ∆Vc, area where damage does not occur even with very high accelerations. Here ∆V (drop height) is so low that the item acts as its own shock isolator. d. <Ac, damage does not occur, even for large ∆V. That’s because the forces generated (F =ma) are within the strength limits of the products. - From Fig. 14.2, a. ∆Vc boundary (vertical boundary line), is independent of the pulse wave shape. b.Ac (to the right of the vertical line) for half sine and sawtooth pulses depends upon ∆V
Shock: Damage Boundary Terminal Peak Sawtooth Pulse /L Half Sine Pulsen Trapezoidal Pulse Velocity change, Inches/ second Figure 14.2 Damage boundary for pulses of same peak acceleration and same velocity change
Shock: Damage Boundary Figure 14.2 Damage boundary for pulses of same peak acceleration and same velocity change
Shock: Damage Boundary C The damage boundary generated with use of a trapezoidal pulse encloses the damage boundaries of all the other waveforms Fragility testing is the process used to establish damage boundaries of products a. It is usually conducted on a shock testing machine. The procedure has been standardized (asTM d3332, Mechanical-Shock Fragility of Products, Using Shock Machines) b Procedure the item to be tested is fastened to the top of a shock machine table and the table is subjected to controlled velocity changes and shock pulses. The shock table is raised to a preset drop height. It is then released, free falls and impacts against the base of the machine it rebounds from the base and is arrested by a braking system so that only one impact occurs
Shock: Damage Boundary c. The damage boundary generated with use of a trapezoidal pulse encloses the damage boundaries of all the other waveforms. - Fragility testing is the process used to establish damage boundaries of products. a. It is usually conducted on a shock testing machine. The procedure has been standardized (ASTM D3332, Mechanical-Shock Fragility of Products, Using Shock Machines). b. Procedure: the item to be tested is fastened to the top of a shock machine table and the table is subjected to controlled velocity changes and shock pulses. The shock table is raised to a preset drop height. It is then released, free falls and impacts against the base of the machine; it rebounds from the base and is arrested by a braking system so that only one impact occurs
Shock: Damage Boundary C For trapezoidal pulses, the programmer is a constant force pneumatic cylinder. The g-level of the trapezoidal pulse is controlled simply by adjusting the com pressed gas pressure in the cylinder. The Av is controlled by adjusting drop height A Shock Testing Machine (1)
Shock: Damage Boundary c. For trapezoidal pulses, the programmer is a constant force pneumatic cylinder. The g-level of the trapezoidal pulse is controlled simply by adjusting the compressed gas pressure in the cylinder. The ∆V is controlled by adjusting drop height. A Shock Testing Machine (1)
