how can I calculate rate of compression?

I want to test rate of compression (mm/s), average Elastic moduli and Plot force-displacement. from the given given text file. Since there are other text files whoes block size are different what changes can i make in my code to make it work for all without manually changing values. For this particula set of value 10% strain rate was applied.

Data = inportdata('DHD_10%_sec_T1.txt'); % read text file: DHD_10%_sec_T1.txt
dL = Data(:,1)'; % relative displacement [mm] data
F = Data(:,2)'; % load = force [N] data
ADF = 10; % adjustment factor for zeroing
L = 39.96; % lenght if block [mm]
w = 25.8666667; % width if block[mm]
th = 25.9; % thickness if block[mm] 
% get the zero point of force
NF = numel(F); % number of elements of F
PosF_L = F > 0; % logical positive
IndV = find(PosF_L); % index of positives
NIndV = numel(IndV); % number of elements of IndV
Nneg = NF-NIndV; % number of elements of negatives
Diff = zeros(1,NIndV-ADF);
for c1 = 1:NIndV-ADF
    Diff(c1) = IndV(c1+ADF)-IndV(c1); % difference between points separated by ADF
end
Diff2 = Diff(2:end)-Diff(1:end-1); % difference between 2 adjacent points
for c2 = 1:c1-1
    if Diff2(c2) ~= 0
        Diff2(c2) = c2; % replaces the elements with increasing counter
    end
end
IndZero = max(Diff2)+Nneg+1; % index of zero F

% zeroed dl and F
dL = dL(IndZero:end)-dL(IndZero); % relative displacement [mm]
F = F(IndZero:end)-F(IndZero); % force [N]

% intensive properties
A = w*L*th; %  area [mm^2]
A = A/1e6; %  area [m^2]
strain = dL/L; % strain [mm/mm]
stress = F/A; % stress [N/m^2 = Pa]

% adjust units
strain = strain*100; % strain [%]
stress = stress/1e6; % stress [MPa]

% locate the ultimate stress
dsigma = diff(stress); % derivative of stress
dsigma = round(dsigma*1000)/1000; % round off dsigma
Ndsig = numel(dsigma); % number of elements of dsigma
MSp = zeros(1,Ndsig); MSpi = MSp; UsigInd = Ndsig; % initial values
for c3 = 1:Ndsig
    [MSp(c3),MSpi(c3)] = max(stress(1:c3)); % maximum stress and its index vectors
    if c3 > 2
        % condition: max is established when the next two are decreasing
        % and the derivative must be negative
        if (MSp(c3) == MSp(c3-1)) && (MSp(c3) == MSp(c3-2)) && (dsigma(c3-1) < 0) && (dsigma(c3-2) < 0)
            UsigInd = c3-2; % index of maximum point
            break;
        end
    end
end

% trim data
cutoff = round(UsigInd*1.15); % maximum index
if cutoff <= Ndsig
    strain = strain(1:cutoff); % strain [%]
    stress = stress(1:cutoff); % stress [MPa]
end

% readjust the zero
Ustr = max(stress); % maximum stress [MPa]
limStr = Ustr*0.01; % 1% of maximum stress [MPa]
Lsig = stress >= limStr; % logical true
LsigInd = find(Lsig); % index of true
zInd = LsigInd(1); % new index
strain = strain(zInd:end)-strain(zInd); % strain [%]
stress = stress(zInd:end)-stress(zInd); % stress [MPa]

% true values
strainT = -log(1-strain/100)*100; % true strain [%]
stressT = stress.*(1-strain/100); % true stress [MPa]
[UCS,UCSi] = max(stressT); % ultimate compressive strength [MPa]
UCstrain = strainT(UCSi); % ultimate compressive strain [%]

% linear regression to determine the compressive modulus
ND = numel(stressT); % number of elements
% initial values
RSQ = zeros(1,ND-2); x = NaN(1,ND); y = x; yf = y; m = RSQ; b = m; dy = b;
for c4 = 1:ND-2
    x = strainT(1:c4+2); % x observed [%]
    y = stressT(1:c4+2); % y observed [MPa]
    m(c4) = (((c4+2)*sum(x.*y))-(sum(x)*sum(y)))/(((c4+2)*sum(x.^2))-(sum(x)^2)) ; % slope of line fit [MPa/% = 100*MPa]
    b(c4) = ((sum(y))-(m(c4)*(sum(x))))/(c4+2); % y-intercept of line fit [MPa]
    yf = m(c4)*x + b(c4); % y fit [MPa]
    SSE = sum((y-yf).^2); % sum of squares error
    SST = sum((y-mean(y)).^2); % sum of squares total
    RSQ(c4) = 1 - (SSE/SST); % coefficient of determination vector
    %xi(c4) = -b/m(c4);
    dy(c4) = abs(y(c4+2) - (m(c4)*x(c4+2)+b(c4)))/UCS; % change in y over UCS
end
[~,ECi] = max(dy >= 0.01); % index of the compressive modulus, 10% cutoff
rsq = RSQ(ECi); % r^2 = coefficient of determination
EC = m(ECi)*100; % compressive modulus [MPa]

% yield values
Ystrain = strainT(ECi+2); % yield strain [%]
Ystress = stressT(ECi+2); % yield stress [%]

Answer 1

[Vinayak]

Hi Manav

From what I noticed in the file you shared, it contains three columns of data. I presume that the other files are in similar format. You could write a custom function that determines the value of strain rate and block sizes based on file name. You can also write a function to go through all files in an existing directory and process them accordingly. Here is a sample code for the given file to calculate the strain rate:

% Get a list of all files in the directory 
directoryPath = 'path/to/your/directory'; % Replace with your directory path 
files = dir(directoryPath); 
fileNames = {files.name}; 

for i = 1:length(fileNames) 
    fileName = fileNames{i}; 
    
    % Ignore directories and hidden files 
    if ~files(i).isdir && ~startsWith(fileName, '.') 
        % Extract the strain rate from the file name 
        strainRate = getStrainRateFromFileName(fileName); 
        
        % Display the strain rate 
        fprintf('Processing file: %s with strain rate: %d%%\n', fileName, strainRate); 
        
        % Process the stress/strain data from the file 
        processData(fullfile(directoryPath, fileName), strainRate); 
    end 
end 

function strainRate = getStrainRateFromFileName(fileName) 
% Regex pattern to match digits followed by a percentage sign 
pattern = '_(\d+)%'; 
tokens = regexp(fileName, pattern, 'tokens'); 
if ~isempty(tokens) 
    strainRate = str2double(tokens{1}{1}); 
else 
    error('Strain rate could not be extracted from the file name.'); 
end 
end 

function processData(filePath, strainRate) 
Data = importdata(filePath); 
ADF = strainRate; 
% ... (rest of the old code) 
end 

You may read more about “regexp” and “dir” in the following documentation:

• https://www.mathworks.com/help/matlab/ref/regexp.html
• https://www.mathworks.com/help/matlab/ref/dir.html