# Calculation of Peak Impact force

#### Karan Ratan

I am a M-tech student working on a project of Drop weight impact testing machine for measuring the crashworthiness of structure. As it will be a lab-scale model, the budget doesn't allow me to include load cells for measuring peak impact force by load-displacement graph.
I am planning to calculate Average impact force as per the deformation obtained in specimen but
for getting the peak impact force(Elastic response) by theoretical approach, can i use the following equation

Impact Force = W √ 2h / δst
Where W = drop weight in N
h = drop height in m
δst = deflection when that drop weight is statically applied in m
Whether this theoretical calculation instead of load cell arrangement can yield me a comparable result of peak impact force ?

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#### berkeman

Mentor
I am a M-tech student working on a project of Drop weight impact testing machine for measuring the crashworthiness of structure. As it will be a lab-scale model, the budget doesn't allow me to include load cells for measuring peak impact force by load-displacement graph.
I am planning to calculate Average impact force as per the deformation obtained in specimen but
for getting the peak impact force(Elastic response) by theoretical approach, can i use the following equation

Impact Force = W √ 2h / δst
Where W = drop weight in N
h = drop height in m
δst = deflection when that drop weight is statically applied in m
Whether this theoretical calculation instead of load cell arrangement can yield me a comparable result of peak impact force ?
Welcome to the PF.

Are you saying that you cannot use simple accelerometers in this setup?

#### Karan Ratan

Impact

Welcome to the PF.

Are you saying that you cannot use simple accelerometers in this setup?

I can use accelerometers but the data acquisition system required to get the readings can cost me. I am trying to keep my project as simple as possible so that it can be affordable for engineering college as an experimental setup of drop ωeight impact test to replace the charpy impact test ωhich can do the charpy impact test, crashωorthiness test and even penetration test.

#### afreiden

I've seen approximations of peak impact force like you are describing, where one makes a couple of basic assumptions -- namely, impulse-momentum, assuming a perfectly elastic collision, along with work-kinetic energy, assuming a triangular pulse shape. Still too many unknowns. These unknowns are peak force, time duration, peak deformation.

I understand that you will be measuring the static deformation as well. So I assume that additional assumptions you've made include linear material behavior and material properties that are independent of rate effects. Is that more or less correct? Did any other assumptions go into your equation? Am I totally off base here and your equation is actually empirical?